OBD-II Code P1682: Ignition Power Problem

What Does P1682 Mean?

P1682 means your Engine Control Module (ECM) sees a disagreement between its two main power sources. The ECM uses two separate power signals to verify the ignition is on. If the voltage in these two circuits differs, the computer logs this fault, preventing the car from starting or causing it to shut off unexpectedly.

Technical definition: The official SAE/ISO definition for P1682 is "Ignition 1 Switch Circuit 2 Malfunction." The ECM detects a voltage difference between the two ignition 1 voltage circuits greater than a specified threshold (typically 3 volts) for less than a second. One circuit is powered by the run/crank relay and the other by the powertrain relay.

Can I Drive With P1682?

No — Do Not Drive. Driving is not recommended. The fault causing this code makes your engine stall suddenly without warning. This happens at any speed, leading to an immediate loss of power steering and power brakes, creating a severe safety risk.

Common Causes

• Faulty Underhood Fuse Box (UBEC) (Very Common) — On many GM vehicles, this is the primary cause. Internal connections, pins, or copper traces inside the fuse box corrode, break, or lose tension, causing an intermittent power loss to the ECM. This is a well-documented defect on models like the GMC Acadia, Chevy Traverse, and Chevy Trailblazer.
🎬 Watch: How to replace a faulty GM fuse box
• Bad Powertrain or Run/Crank Relay (Common) — These small, cube-shaped plugs in your fuse box control power to the ECM. They fail internally, especially in cold weather due to moisture or frost, causing a no-start condition. This is the most frequent cause for the Chevy Cruze, as noted in GM TSB PI1422.
• Loose or Corroded Fuses or Terminals (Common) — The female terminals in the fuse box socket spread apart, creating a poor connection. Wiggling the ECM or ignition-related relays temporarily makes the car start, pointing directly to a loose socket rather than a failed component.
• Poor Engine/Chassis Ground Connection (Less Common) — A loose, corroded, or broken ground strap between the engine, chassis, or battery causes erratic voltage readings. The ECM relies on a stable ground reference; a bad ground makes it perceive a false voltage discrepancy between its power feeds, triggering P1682.
• Wiring Problems (Open/Short) (Less Common) — A wire in the ignition circuit frays, breaks, or shorts to ground. On some GM trucks, TSB 21-NA-032 points to a compromised wire crimp within a fuse box connector. A resistance of 5 ohms or greater in a power or ground circuit sets this code.
• Faulty Ignition Switch (Less Common) — The electronic part behind your key cylinder wears out and sends an improper voltage signal. While it causes P1682, it is frequently misdiagnosed, and the actual problem lies within the fuse box 🎬 Watch this walkthrough to diagnose ignition circuit malfunctions or relays on most popular vehicles.
• Weak or Dead Battery / Bad Connection (Rare) — A bad battery connection, especially after replacement, triggers this code. The code points to a discrepancy between two circuits, not a total loss of voltage, making a dying battery an infrequent root cause.
• Faulty Engine Control Module (ECM) (Very Rare) — It is extremely rare for the ECM itself to fail. The ECM is robust and logs this code due to faulty incoming power. Exhaustively rule out wiring, relays, and the fuse box before condemning the computer.

Symptoms

• Engine will not start (cranks but won't fire) — You turn the key, the engine turns over normally, but it never actually starts and runs. This is the primary symptom.
• Engine stalls while driving — The engine suddenly shuts off while you are driving without warning, creating a major safety hazard.
• No-crank, no-start condition — You turn the key and nothing happens at all; there is no clicking and the engine does not turn over.
• Check Engine Light is on — The Malfunction Indicator Lamp (MIL) illuminates on your dashboard.
• Reduced Engine Power message — Your vehicle displays a warning message and enters limp mode with limited engine power and poor acceleration.
• Traction Control / ABS lights on — When the ECM loses power intermittently, it disrupts communication with other modules, illuminating warning lights for the Traction Control System (TCS) and Anti-lock Braking System (ABS).
• Engine continues to run after key is turned off — In rare cases, the fault causes the engine to remain running even after the ignition key is turned to the 'OFF' position and removed.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this code.

Common Fixes & Costs

• Replace the Run/Crank or Powertrain Relay — Parts: $15-$30, Labor: $0, ~0.1 hr book time (DIY)
• Repair Corroded Fuse Box Terminal/Wire — Parts: $15-$30, Labor: $150-$350, ~2 hr book time (Professional)
• Replace the Underhood Fuse Box (UBEC) — Parts: $250-$450, Labor: $150-$300, ~2.0 hr book time (Professional)
• Clean or Repair Main Ground Connections — Parts: $0-$10, Labor: $50-$150, ~0.5 hr book time (DIY)
• Replace the Ignition Switch — Parts: $50-$250, Labor: $110-$180, ~1.5 hr book time (Intermediate)

DIY vs Professional

• Replace the Run/Crank or Powertrain Relay — Beginner:
  Tools: None, or relay puller pliers.
• Clean or Repair Main Ground Connections — Beginner:
  Tools: Socket set, wire brush, sandpaper.
• Replace the Ignition Switch — Beginner:
  Tools: Socket set, trim removal tools, screwdrivers.
• Replace the Underhood Fuse Box (UBEC) — Beginner:
  Tools: Socket set, screwdrivers, trim removal tools.
• Repair Corroded Fuse Box Terminal/Wire — Beginner:
  Tools: Specialized terminal removal tools, wire crimpers, soldering iron, drill.

Used vs. New Parts: Buying Guide

When a used part is worth it: For an expensive part like an Underhood Fuse Box (UBEC), a used part from a low-mileage, non-accident vehicle is a cost-effective option if the new part is over $400 or discontinued. Always buy new relays.

Donor-vehicle mileage cap: roughly under 60000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Match the part number EXACTLY. Trim levels and options change the internal wiring of the fuse box.
• Avoid parts from the 'Rust Belt' or high-humidity areas, as they are likely to have the same corrosion issues.
• Inspect the used part for any signs of corrosion, melted plastic, or previous repair attempts.

Decision logic:

• If The required part is a relay → Always buy new. The cost saving is negligible and the risk of a used relay failing is high.
• If The part is a UBEC and a new OEM part is available for < $300 → Buy new OEM. The peace of mind and warranty outweigh the savings from a used part.
• If The UBEC is > $400 new or discontinued → A used part from a reputable salvage yard with a warranty is a reasonable choice. Verify the donor vehicle's history.

Warranty tradeoff: Used parts typically have a 30-90 day part-only warranty, meaning you are liable for repeat labor costs if it fails. New aftermarket parts offer 1-year to limited-lifetime warranties. New OEM parts carry a 1-2 year warranty.

Worst-case if a used part fails: $300-$600. If a used fuse box fails after the warranty period, you pay for a new part plus the labor to replace it a second time.

What Happens If You Wait — Timeline

1. First Occurrence: An intermittent no-start or a single, unexpected stall. The Check Engine Light comes on with P1682. The car restarts and runs fine for days or weeks. (MPG impact: 0%% · Added cost: $0)
2. Weeks to Months: No-start or stalling events become frequent and predictable (e.g., only on cold mornings). The vehicle is unreliable, and repeated cranking strains the starter and battery. (MPG impact: 0%% · Added cost: $100-$250 for a potential tow if stranded.)
3. 1-4 Months: The vehicle consistently fails. The root cause, like a loose terminal or cracked trace, arcs and creates heat, melting plastic in the fuse box and making the repair more complex. (MPG impact: 0%% · Added cost: $250-$1000. Includes multiple tows and replacing a starter motor or battery damaged by excessive cranking.)
4. Immediate or 4+ Months: Catastrophic failure occurs. The engine stalls at highway speed, resulting in a complete loss of power assist to steering and brakes, potentially causing an accident. (MPG impact: N/A% · Added cost: $2,000 to $20,000+. Represents the cost of accident repairs, insurance deductibles, or total vehicle loss.)

Cost of Not Fixing It

• Immediate: Catastrophic safety risk. The engine stalls at any speed without warning, leading to a loss of power steering and brakes. (Added cost: Potential for accident-related costs, from insurance deductibles to total loss of vehicle.)
• Days to Weeks: Increased frequency of no-start or stalling events, leaving you stranded. Repeated cranking strains the starter and battery. (Added cost: $200-$500 for towing and potential starter/battery replacement.)
• 1+ Month: The vehicle becomes completely unreliable. Root causes like fuse box corrosion worsen, making repair more difficult and expensive. (Added cost: The cost of the original repair plus additional labor to address worsened corrosion or damage.)

Diagnosis Steps

1. Swap the Relays
   Locate the Run/Crank and Powertrain (or ECM) relays. Find another identical relay in the box (like for the horn or A/C) and swap it with the suspect relay. If the car starts, you have a bad relay. This is the most common fix for the Chevy Cruze.
   Tools: Owner's Manual (to locate relays) (Beginner)
2. Inspect and 'Wiggle' Fuses and Relays
   Open the underhood fuse box. With the key off, push down firmly on each ECM, PCM, IGN, or Run/Crank relay to ensure they are seated. Gently wiggle the relays while an assistant attempts to start the vehicle. If wiggling makes the car start, you have a loose socket connection.
   Tools: Owner's Manual (to locate fuses/relays) (Beginner)
3. Check the Battery and Connections
   Ensure your battery is fully charged (above 12.4 volts) and the terminals are clean and tight. A loose connection causes unpredictable electrical drops, especially if the issue started after a battery replacement.
   Tools: Multimeter, Battery Terminal Brush (Beginner)
4. Visually Inspect the Fuse Box (UBEC)
   With the battery disconnected, unbolt and carefully lift the underhood fuse box to inspect the large connectors underneath. Look for green or white corrosion, burnt plastic, or melted terminals. On GM Lambda platforms (Acadia, Traverse), check connector X3, pin 51, a known failure point.
   Tools: Socket Set (Intermediate)
5. Perform a Voltage Drop Test at the Fuse Box
   When the no-start condition is present, place the multimeter's black lead on the negative battery terminal. With the key ON, use the red lead to probe the metal test points on top of the fuses for the ECM and Ignition circuits. You should see battery voltage (12.0V+). If a fuse shows low voltage, the problem is upstream.
   Tools: Multimeter, Vehicle Wiring Diagram (Intermediate)
6. Inspect and Clean Main Ground Connections
   Locate, remove, and clean the main chassis and engine ground connections (e.g., G103, G105, G110). Use a wire brush to clean the terminal, bolt, and mounting surface until they are bright, bare metal. A poor ground creates a floating voltage reference and triggers this code.
   Tools: Socket Set, Wire Brush (Intermediate)
7. Bench Test the Suspect Relay (Quantitative Check)
   Remove the suspect relay. Test the resistance between pins 85 and 86 (coil circuit). A good 12V relay reads between 50 and 120 Ohms. Check continuity between pins 30 and 87; there should be none. Apply 9V power to pins 85 and 86. The relay should click, and you should now have continuity between pins 30 and 87.
   Tools: Multimeter, 9V Battery or Jumper Wires, Relay Puller Pliers (Advanced)
8. Analyze Live Scan Tool Data (Pro Tip)
   Connect a professional scan tool. Monitor the ECM parameters for 'Ignition 1 Voltage' and 'EC Ignition Relay Feedback'. With the key ON, both should read close to battery voltage. A discrepancy greater than 3.0 volts confirms the fault condition and identifies which circuit is dropping out.
   Tools: Professional Scan Tool (Advanced)
9. Check for Voltage at the ECM
   Identify the two ignition voltage input pins at the ECM connector. With the key ON and the connector plugged in, carefully back-probe these pins. A reading below 9 volts on one circuit while the other is at battery voltage definitively confirms the voltage drop is reaching the computer. Stop DIY and tow to a shop if voltage drops are confirmed here but the fuse box tests good.
   Tools: Multimeter, Vehicle Wiring Diagram, T-pins (Advanced)

When This Code Triggers (Freeze-Frame Conditions)

• DTC Set: P1682 (This code indicates a voltage mismatch between two ignition circuits.)
• Engine State: Cranking or Running (The fault occurs during startup (crank-no-start) or while driving (stalling), often when the engine is warm.)
• System Voltage: 10-14V (The code sets when the ECM is powered and sees a discrepancy, not necessarily from low overall voltage. The DTC check runs continuously when ignition is ON and voltage is >6V.)
• Ignition 1 Signal vs. Relay Feedback: >3V Difference (The core condition for the code setting is when the ECM sees a voltage difference greater than 3 volts between its two main power feeds for more than a couple of seconds.)

Related Codes

• P0689 — This code, 'ECM/PCM Power Relay Sense Circuit Low,' frequently appears with P1682. Seeing both codes together strongly points to a problem with the powertrain relay or its circuit within the underhood fuse box. TSB 19-NA-276 identifies a faulty fuse box terminal as the cause for both codes appearing simultaneously.
• P0685 — This code means 'ECM/PCM Power Relay Control Circuit/Open.' It refers to the ECM's ability to command the relay on or off. If you hear the relay click when the key is turned ON, the control circuit (P0685) is working, and the issue is with the relay's output (P1682). If there is no click, the problem is the control circuit or the ECM.
• U0100 — This code means 'Lost Communication With ECM/PCM.' If the ECM loses power completely due to the fault causing P1682, other modules cannot talk to it, logging U0100. P1682 is the cause, while U0100 is the effect.
• P0101 — This code, 'Mass Air Flow (MAF) Sensor Performance,' appears alongside P1682 on some 2019-2021 GM trucks. GM TSB 21-NA-032 warns that a compromised wire crimp in the fuse box causes both codes. Do NOT replace the MAF sensor if you see these two codes together.

Climate & Environmental Factors

• Cold Weather: Low temperatures cause moisture inside a failing relay to freeze, preventing the internal contacts from making a connection. This is a very common cause of a no-start with P1682 on vehicles like the Chevrolet Cruze.
• Hot Weather: High under-hood temperatures cause a hairline crack in a thin copper trace inside the fuse box to expand, breaking the electrical connection. This leads to the engine stalling after running for a while and refusing to restart until it cools down.
• High Humidity / Road Salt: In humid climates or regions where road salt is used, moisture and salt enter the underhood fuse box, causing severe corrosion on terminals, pins, and internal traces. This corrosion creates high resistance and triggers P1682.

How to Talk to a Mechanic About This Code

Say this: "I have a crank/no-start issue with a P1682 code. Based on GM TSBs, please start by checking the ignition and powertrain relays, and the integrity of the underhood fuse box terminals and grounds, before diagnosing the ignition switch or ECM."

This signals you're an informed customer. It directs the technician to the most common, well-documented failure points first, saving diagnostic time and preventing them from immediately quoting an expensive, incorrect repair.

Avoid saying:

• 'My car won't start, can you fix it?'
• 'The check engine light is on, I think it's the computer.'
• 'Just do whatever it takes to get it running.'

Questions to ask before authorizing the repair:

• Did you perform a relay swap? Did that change the symptoms?
• Did you find voltage drop at the ECM/Ignition fuses or at the ECM connector pins?
• If you are recommending a fuse box replacement, did you find evidence of corrosion, heat damage, or loose terminals underneath it?
• Can you confirm the main engine and chassis grounds were inspected and cleaned?

Where to Take It: Dealer vs Independent vs Chain

• Dealer:
  Best for: Vehicles under warranty., Complex electrical issues where access to manufacturer-specific tools (GM MDI) and the latest TSBs is critical., When you want the highest probability of a correct first-time diagnosis, regardless of cost.
  Downsides: Highest labor rates., Defaults to replacing the entire fuse box assembly when a less expensive terminal repair is possible. (Typical cost: +50% vs. baseline)
• Independent Shop: Best fit. An experienced independent technician is familiar with these common GM electrical faults and provides a cost-effective repair. Vet the shop by asking if they are comfortable diagnosing complex electrical issues.
  Best for: Out-of-warranty GM vehicles with this common code., Cost-conscious owners who can find a shop with a strong reputation for electrical diagnostics.
  Downsides: Shop quality varies greatly; a shop without good electrical skills struggles or misdiagnoses., May be less familiar with specific TSBs than a dealer. (Typical cost: +0% vs. baseline)
• Chain Shop: AVOID. The diagnostic process for P1682 requires tracing circuits beyond the skill set of a typical quick-lube technician. The risk of misdiagnosis is very high.
  Best for: Simple, unambiguous repairs like a battery replacement or oil change.
  Downsides: Technician skill is highly variable and often not specialized in electrical diagnosis., Likely to replace the wrong part (ignition switch) or be unable to diagnose the issue if a simple relay swap fails. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the estimated repair cost exceeds 50% of the car's private-party value, seriously consider selling the car as-is or trading it in rather than repairing it.

• Car worth $3500, fix is $1000: Borderline. A $1000 fuse box replacement is a significant investment in a $3500 car. Get a second opinion. If the fix is just a $20 relay, it's an obvious 'Fix it'.
• Car worth $15000, fix is $1000: Fix it. The repair cost is well under the threshold and restores a valuable vehicle to safe, working order.
• Car worth $2000, fix is $1000: Walk away. The repair cost is 50% of the car's value. It is not economical to proceed unless the rest of the car is in pristine condition.

What Scan Tool You Need for This Code

Minimum: A tool that reads live data streams from the Engine Control Module (ECM).

A $20 basic code reader only tells you that code P1682 is present. It cannot show you the live 'Ignition 1 Voltage' and 'Relay Feedback' data streams. Seeing the voltage discrepancy on a scanner is the key to confirming the fault.

Budget: BlueDriver Pro or Foxwell NT301 (~$100) — Connects to your smartphone and allows you to view and graph live data streams from the ECM. This is sufficient to see the voltage difference between the two ignition circuits.

Mid-range: Foxwell NT510 Elite with GM Software or Autel MaxiCOM MK808S (~$180-350) — Offers full-system diagnostics, including reading manufacturer-specific codes and data PIDs for GM. The Autel MK808S provides bidirectional control, allowing you to command relays to test their function directly.

Professional: Autel MaxiSys Series (MS906+) or Launch X431 Series (~$600-1500) — Provides full bidirectional control, access to wiring diagrams and TSBs directly on the tool, and advanced functions like ECU coding. These are professional-grade tools offering dealership capabilities.

How to Clear the Code After You Fix It

1. Fix the underlying mechanical or electrical issue.
2. Reconnect the battery if it was disconnected for the repair.
3. Use an OBD-II scan tool to formally clear the P1682 and any related trouble codes.
4. Perform a complete drive cycle to allow readiness monitors to run.

Drive cycle (~20 minutes): Start the car from cold (sit overnight). Idle for 2-3 minutes. Drive in mixed city/highway conditions, including steady cruising at 55-60 mph for at least 5-10 minutes. Allow the vehicle to cool down completely and repeat if necessary.

Readiness monitors affected: Comprehensive Component Monitor, Misfire Monitor

Before emissions retest: drive at least 50 miles to fully set monitors.

Watch out for:

• Simply disconnecting the battery clears the code but resets all readiness monitors to 'Not Ready', failing an emissions test.
• The code returns immediately if the root cause (e.g., bad fuse box, loose relay) is not actually fixed.
• Not driving long enough or at varied enough speeds prevents monitors from completing their self-checks.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: Automatic failure. The presence of a Check Engine Light from code P1682 instantly fails the OBD-II portion of the smog check. All readiness monitors must also be 'Ready'.
• New York: Automatic failure. The NYS vehicle inspection includes an OBD-II scan. An illuminated Malfunction Indicator Lamp (MIL) for any code results in a failed inspection.
• Texas: Automatic failure in applicable counties. In counties requiring an emissions test, an illuminated Check Engine Light is an automatic fail.

Most Commonly Affected Vehicles

• Chevrolet Cruze (2011-2015) — Extremely prone to a faulty KR75 Engine Controls Ignition Relay (P/N 13595908), especially in cold weather due to internal frost buildup, as documented in GM TSB PI1422.
• GMC Acadia (2007-2017) — Known for a design flaw in the underhood fuse box (UBEC) where terminal 51 in connector X3 corrodes or loses tension. Detailed in GM TSB 19-NA-276 and often appears with code P0689.
• Chevrolet / Buick / Saturn Traverse / Enclave / Outlook (2007-2017) — Platform-mates with the GMC Acadia suffering from the exact same common failure of the underhood fuse box terminal (pin 51, connector X3) as detailed in TSB 19-NA-276.
• Chevrolet / GMC Trailblazer / Envoy (2002-2009) — Known to have a thin copper wire trace inside the fuse block that develops a hairline crack, causing intermittent no-start conditions when hot. The fuse box is often discontinued, requiring soldering to repair.
• Chevrolet / GMC Silverado / Sierra (2014-2021) — TSB 21-NA-032 points to a bad wire crimp in the UBEC (connector X3, pin H6) for 2019-2021 models, which also sets code P0101. TSB PIT5253A identifies a faulty ignition relay for 2014-2015 models.
• Pontiac G6 (2005-2010) — Commonly experiences P1682 due to a loose relay socket in the fuse box. The female terminals spread apart, creating a poor connection diagnosed by wiggling the relay.
• Chevrolet HHR / Cobalt (2006-2011) — Experiences P1682 due to issues within the underhood fuse box, from bad relays to poor connections at the 15A ECM fuse or loose main connector bolts.
• Chevrolet Impala / Malibu (2008-2014) — Suffers from the same internal cracked copper trace inside the underhood fuse box that affects the Trailblazer, leading to stalling in hot weather.
• Volkswagen / Audi Golf, Jetta, A3, etc. (2001-2015) — For these vehicles, P1682 means 'CAN Data Bus, ABS – Implausible Signal.' This is a communication error with the ABS module and is completely unrelated to the ignition power issue seen in GM vehicles.

Manufacturer-Specific Notes

• General Motors (Chevrolet, GMC, Buick, Pontiac): On GM vehicles, this code is defined as 'Ignition 1 Switch Circuit 2'. The cause is overwhelmingly a faulty underhood fuse box (UBEC) or a bad relay, not the ignition switch itself. Numerous TSBs point to specific, known failure points.
• Audi / Volkswagen: On these brands, P1682 means 'CAN Data Bus, ABS – Implausible Signal,' which is an unrelated issue regarding communication with the anti-lock brake system.
• Ford / Citroen / Peugeot: On some vehicles from these brands, P1682 points to a 'Metering Oil Pump Malfunction,' a completely different engine system issue.
• Hyundai: For some Hyundai models, P1682 is defined as 'Condenser Fan Relay Circuit High,' indicating a fault in the A/C condenser fan control circuit.

Real Owner Stories

2011 Chevy Cruze with 110K miles - No start in cold weather.

Car cranked but would not start on cold mornings. Code P1682 was present. The issue was intermittent but worsening.

What they tried:

1. Tested the battery, which passed.
2. Considered replacing the ignition switch but checked easier components first.

Outcome: Owner found GM TSB PI1422, pointing to the KR75 ignition relay. They swapped the suspect relay with the identical A/C relay. The car started immediately. A new OEM relay (P/N 13595908) was installed for $15, permanently fixing the problem.

Lesson: On a Chevy Cruze with P1682, especially during a cold-weather no-start, the ignition relay is the primary suspect. A simple relay swap is a free, definitive diagnostic step.

2014 GMC Acadia with ~100K miles - Intermittent stalling and 'Reduced Power' message.

Vehicle randomly stalled at stoplights and displayed 'Reduced Engine Power'. Codes P1682 and P0689 were present.

What they tried:

1. Suspected the ignition switch.
2. A shop tightened the main power studs on the fuse box, which did not fix the problem.

Outcome: Following GM TSB 19-NA-276, a technician inspected the connectors underneath the underhood fuse box (UBEC). Pin 51 of the X3 connector showed severe heat discoloration. The fix was replacing the fuse box and splicing in a new wire terminal pigtail (GM P/N 84757974), resolving both codes.

Lesson: If P1682 pairs with P0689 on a GM Lambda-platform vehicle (Acadia, Traverse, Enclave), the cause is the known fuse box terminal failure. Inspect connector X3 pin 51 immediately.

2007 Chevy Trailblazer SS at 120K miles - Stalling when hot.

Engine ran fine cold, but stalled at operating temperature. It cranked but would not restart until cooled down. Code P1682 was stored.

What they tried:

1. Replaced the ignition switch, battery, and powertrain relays. The problem persisted.

Outcome: Owner disassembled the discontinued fuse box and found a hairline crack in a thin 20-gauge copper trace. Engine heat caused the crack to expand and break the connection. Soldering a new wire to bypass the break permanently resolved the stalling.

Lesson: For heat-related stalling on a Trailblazer, the fuse box is the culprit. Inspect the fuse box for internal breaks before replacing expensive parts.

2008 Pontiac G6 2.4L - Intermittent stalling and no-start.

Car occasionally stalled at stoplights or failed to start, eventually dying completely with code P1682.

What they tried:

1. Tested all related fuses and replaced relays with new ones. The problem remained.

Outcome: While pressing on the new relays, the owner noticed the run/crank relay was loose in its socket. Wiggling the relay while cranking started the engine immediately. The female terminals in the fuse box had spread apart. The owner used a small pick tool to bend the terminals back together for a tighter fit, solving the problem.

Lesson: Physically check if relays feel loose in their sockets. A 'wiggle test' while trying to start the car pinpoints loose connections within the fuse box.

How to Prevent This Code From Triggering

• Clean and Protect Fuse/Relay Terminals (Every 3-5 years, or if working in the fuse box) — Corrosion on relay and fuse terminals creates high resistance, causing voltage drops and heat. Periodically removing relays, cleaning the male blades, and applying dielectric grease prevents moisture intrusion.
• Inspect and Clean Main Ground Straps (Every 30,000 miles) — The ECM relies on a clean ground path to measure voltage accurately. Engine vibration and road grime cause ground connections to loosen or corrode. Cleaning contact points to bare metal ensures a stable voltage reference.
• Ensure Fuse Box Cover is Sealed (Every time the fuse box is opened) — The underhood fuse box cover has a rubber seal to keep water out. If damaged or unlatched, water enters and causes catastrophic corrosion to internal traces and terminals, a primary cause of P1682.
• Consider Proactive Relay Replacement (Once per 100K miles for critical relays) — Relays are mechanical devices with a finite lifespan. For critical functions like the powertrain or ignition relay, replacing them proactively after 100,000 miles prevents a sudden no-start or stalling situation.

Frequently Asked Questions

What does 'Ignition 1 Switch Circuit 2' actually mean?

It means the ECM uses two separate wires to confirm the ignition is on. The code sets when the voltage on 'Circuit 2' differs from 'Circuit 1' by more than 3 volts, indicating a power loss. This mismatch triggers the fault.

Is it safe to drive with a P1682 code?

No. The primary risk is sudden engine stalling at any speed without warning. This causes an immediate loss of power steering and brakes, creating a dangerous driving situation.

Can I just replace the battery to fix P1682?

Replacing the battery rarely fixes this code, as it indicates a voltage difference between two specific circuits, not a general low battery. However, you must ensure your battery connections are clean and tight, because a poor connection causes unpredictable electrical drops.

My car won't start. Is the ignition switch the problem?

While a bad ignition switch causes this code, on many GM vehicles the problem is a bad relay or a faulty underhood fuse box. Always check the $20 relays first before assuming it's the more expensive ignition switch.

Why does my car only have this problem when it's cold or hot?

Temperature changes affect electrical connections. In cold weather, moisture freezes inside a relay, preventing contact (common on the Chevy Cruze). In hot weather, a hairline crack in a fuse box copper trace expands and breaks the connection (common on the Chevy Trailblazer).

I replaced the relay and the code is still there. What's next?

If a relay swap fails, the next most likely cause is a poor connection at the fuse box. Inspect the terminals underneath the fuse box for corrosion or heat damage. You must rule out a loose socket or melted pin before replacing expensive modules.

Can a bad ground wire cause code P1682?

Yes, because the ECM needs a solid ground connection to accurately read voltages. A loose or corroded engine ground creates an unstable reference, making the ECM perceive a false discrepancy between its power feeds. Cleaning the main ground points to bare metal is a critical diagnostic step.

My car also has a P0101 (MAF Sensor) code. Should I replace the MAF sensor?

No, do not replace the MAF sensor without further diagnosis on a 2019-2021 GM truck. TSB 21-NA-032 warns that a wiring issue in the underhood fuse box causes both P1682 and P0101 to set simultaneously. The root cause is the power supply, not the sensor.

Key Takeaways

• Code P1682 indicates a voltage mismatch greater than 3 volts between the engine computer's two main power feeds, causing sudden engine stalling or a no-start condition.
• On 2007-2017 General Motors vehicles, the root cause is rarely the ignition switch; it is almost always a faulty $20 ignition relay or a corroded terminal inside the underhood fuse box.
• Swap the suspect run/crank relay with an identical relay (like the A/C or horn relay) in the fuse box as your free, 5-minute first diagnostic step.
• If code P0689 appears alongside P1682 on a GM SUV, immediately inspect pin 51 on connector X3 under the fuse box for heat damage, as outlined in TSB 19-NA-276.