OBD-II Code P0690: Engine Computer Power Problem

What Does P0690 Mean?

P0690 means the Powertrain Control Module (PCM) is receiving excessive voltage from its power source. The PCM requires steady voltage and uses a 'sense' circuit to monitor power from the main relay. When it detects voltage exceeding manufacturer limits on this circuit, it triggers P0690 to warn of an unstable power supply.

Technical definition: ECM/PCM Power Relay Sense Circuit High. The PCM detected voltage on the power relay's feedback (sense) circuit exceeding manufacturer limits. When the PCM expects a low voltage signal (relay off), it instead sees constant battery voltage, indicating a short to power or a relay stuck in the 'on' position.

Can I Drive With P0690?

Yes, But With Caution. You can drive, but the engine risks stalling unexpectedly—a major safety hazard in traffic. Continuing to drive subjects the Powertrain Control Module (PCM) to repeated voltage stress, risking permanent damage that adds $800-$1,500 to the repair bill. Diagnose the vehicle immediately to avoid being stranded.

Common Causes

• Faulty ECM/PCM Power Relay (Very Common) — The PCM power relay gets stuck in the 'on' position or shorts internally, delivering constant voltage. This is the most frequent cause of P0690.
• Corroded Fuse Box Contacts or Blown Fuse (Common) — Corrosion or damage on the contacts where the relay plugs into the fuse box causes unstable voltage readings. A blown ECM/PCM fuse also triggers erratic voltage spikes.
• Wiring Shorted to Power (Common) — The 'sense' wire monitoring PCM voltage gets damaged, frayed, or corroded, touching a 12V power source. This forces the PCM to read constant high voltage.
• Poor Ground or Battery Connections (Less Common) — A loose, corroded, or broken ground wire at the PCM or battery creates a voltage differential that the PCM interprets as a high voltage condition.
• Failing Alternator (Rare) — A faulty alternator voltage regulator overcharges the entire electrical system, sending excessive voltage to the PCM relay.
• Improperly Installed Aftermarket Accessories (Rare) — Aftermarket electronics (remote starters, alarms) improperly wired into the vehicle's power system draw excessive current or create voltage feedback.
• Defective Powertrain Control Module (PCM) (Very Rare) — The PCM's internal voltage-sensing circuits break down due to moisture or corrosion, reporting a false high-voltage problem. Rule out all other causes before replacing the PCM.

Symptoms

• Engine Cranks But Won't Start (or Hard Starting) — The engine cranks but fails to start because the PCM enters self-preservation mode or lacks stable power. Starting may take significantly longer than usual.
• Engine Stalls While Driving — The engine shuts off unexpectedly due to intermittent power loss to the PCM, creating a serious safety hazard.
• Erratic Electrical Malfunctions — Secondary modules and sensors on the network malfunction due to the PCM's unstable power supply.
• Check Engine Light is On (also visible on scanner) — The primary and sometimes only initial warning of the voltage fault.
• No Communication with Scan Tool (scan-tool only — no driver-felt sign) — The scan tool cannot communicate with the PCM because the module fails to power on.

Diagnostic Flowchart

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

Common Fixes & Costs

• Replace the ECM/PCM Power Relay — Parts: $15-$50, Labor: $0-$50, ~0.2 hr book time (DIY)
• Replace a Blown Fuse or Clean Contacts — Parts: $1-$10, Labor: $0-$50, ~0.5 hr book time (DIY)
• Install Ford Fuse 27 Relocation Kit — Parts: $20-$50, Labor: $100-$200, ~1.2 hr book time (DIY)
• Repair Damaged Wiring or Connectors — Parts: $10-$50, Labor: $150-$450, ~2.5 hr book time (Professional)
• Clean or Repair Ground Connections — Parts: $1-$10, Labor: $50-$150, ~0.8 hr book time (DIY)
• Replace the Powertrain Control Module (PCM) — Parts: $800-$1,500, Labor: $150-$300, ~1.5 hr book time (Professional)

Used vs. New Parts: Buying Guide

When a used part is worth it: For vehicles over 10 years old or 150k miles where a new module exceeds 20% of the car's value. Buy from a reputable recycler with a warranty.

Donor-vehicle mileage cap: roughly under 100000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Match the part number exactly. Superseded numbers fail without special programming.
• Ensure the donor vehicle matches your engine, transmission, and drivetrain configuration.
• Require a minimum 90-day warranty and return policy.

Decision logic:

• If The part is a simple relay → Always buy new. Cost savings are negligible and not worth the risk of an unknown history.
• If The part is a complex module (PCM/TIPM) and the vehicle is under 10 years old → Buy a new or professionally remanufactured unit with a lifetime warranty to avoid security system conflicts.
• If The part is a TIPM or IPDM with known internal relay failure issues → Buy a remanufactured unit with upgraded, re-engineered failure points. It outlasts both new OEM and used parts.

Warranty tradeoff: Used parts offer 30-90 day part-only warranties. Remanufactured units provide 1-year to lifetime warranties. New OEM parts carry 12-month/12,000-mile warranties if dealer-installed.

Worst-case if a used part fails: $500-$1000 for repeat diagnostic and programming labor if a used module fails or triggers anti-theft lockouts.

What Happens If You Wait — Timeline

1. 0-1 month: Check Engine Light illuminates. Vehicle experiences occasional hard starting or brief hesitation when cranking. (MPG impact: 0%% · Added cost: $0)
2. 1-3 months: Engine cranks but fails to start, requiring multiple key cycles. Unexpected engine stalling occurs at low speeds. (MPG impact: 0-2%% · Added cost: $100-$250 (Tow truck fees))
3. 3-6 months: Constant high voltage causes thermal stress on the PCM's internal voltage regulation circuits. Frequent no-starts make the vehicle unreliable. (MPG impact: 2-5%% · Added cost: $250-$500 (Multiple tows and diagnostic fees))
4. 6+ months: Catastrophic failure of the PCM's internal circuits. The vehicle will not start. A $20 relay problem has destroyed the computer. (MPG impact: N/A (Vehicle is inoperable)% · Added cost: $1,100-$2,500+ (PCM replacement and programming))

Cost of Not Fixing It

• Immediate: High risk of engine stalling in traffic or a no-start condition, leaving you stranded. (Added cost: $100-$300 (Towing and emergency diagnostic fees))
• 1-3 months: Continued high voltage stresses and destroys the PCM's internal circuits. A $20 relay fix escalates into a major repair. (Added cost: $800-$1500+ (PCM replacement and programming))
• 3+ months: Catastrophic PCM failure renders the vehicle completely inoperable. Electrical instability damages other sensitive CAN bus modules. (Added cost: $1500-$3000+ (PCM and secondary module replacements))

Diagnosis Steps

1. Check for Other Codes
   Use an OBD-II scanner to read all stored codes. Address communication (U-codes) or fuel system codes first, as they often pinpoint the root cause.
   Tools: OBD-II Scanner (Beginner)
2. Swap the PCM Relay (The 'Shade Tree' Test)
   Swap the PCM relay with an identical relay from a non-critical system (like the horn or A/C clutch). If the vehicle starts or the problem changes, the original relay is bad. Replace it.
   Tools: None (or Relay Puller Pliers) (Beginner)
3. Inspect Fuses and Relay Sockets
   Locate the main fuse box. Inspect the ECM/PCM fuse for a blown filament. Check the relay's pins and socket for corrosion, melting, or burning.
   Tools: Owner's Manual, Flashlight (Beginner)
4. Test the Relay Circuit Voltage
   With the key on, back-probe the PCM relay's 'sense' circuit wire at the PCM connector. A constant reading of battery voltage (12.6V+) when the relay is commanded OFF confirms a short to voltage or a stuck relay.
   Tools: Multimeter, Vehicle-Specific Wiring Diagram, Back-probe Kit (Advanced)
5. Inspect Wiring and Grounds
   Visually inspect the wiring harness between the PCM and fuse box for chafing or melting. Ensure the main engine and PCM ground straps are clean, tight, and rust-free.
   Tools: Flashlight, Socket Set, Wire Brush (Intermediate)
6. Check Relay Coil Resistance
   Remove the relay and test across the coil terminals (pins 85 and 86) with a multimeter set to Ohms. A reading of OL (Open Loop) or 0 Ohms means the internal coil is broken or shorted.
   Tools: Multimeter (Advanced)
7. Perform a Voltage Drop Test on the Ground Circuit
   Place the multimeter's red lead on the PCM relay's ground pin and the black lead on the negative battery terminal. With the key on, a reading above 0.1 volts (100mV) indicates a poor ground connection requiring repair.
   Tools: Multimeter (Advanced)
8. Test the Charging System
   With the engine running, test voltage at the battery terminals. A reading over 15V indicates a faulty alternator voltage regulator overcharging the system.
   Tools: Multimeter (Intermediate)

When This Code Triggers (Freeze-Frame Conditions)

• Fault Trigger: Key On or Cranking (Detected immediately when the ignition turns on or during engine cranking, before the engine starts.)
• System Voltage: 12.6V+ (Triggers when the PCM sense line sees battery voltage while expecting near 0V (relay commanded off).)
• Engine RPM: 0 or <300 RPM (Shows 0 RPM or low cranking RPM because the fault prevents the engine from starting.)
• Engine Load: 0% (Engine load is zero because the fault prevents the engine from running.)

Related Codes

• P0689 — ECM/PCM Power Relay Sense Circuit Low. The opposite of P0690. P0690 means voltage is present when it shouldn't be (short to power). P0689 means voltage is absent when it should be present (short to ground or dead relay).
• P0688 — ECM/PCM Power Relay Sense Circuit Open. Indicates a complete loss of signal, pointing to a broken wire, disconnected connector, or completely dead relay.
• U0109 — Lost Communication With Fuel Pump Control Module. Frequently pairs with P0690 on Ford trucks due to the shared power circuit in the fuse box (Fuse 27 issue).
• P1682 — Ignition 1 Switch Circuit 2. Accompanies P0690 on GM vehicles, indicating a discrepancy between ignition voltage signals caused by a fault in the fuse block or ignition switch.

Climate & Environmental Factors

• High Humidity / Salt Belt Regions: Moisture and road salt accelerate corrosion on wiring, fuse box terminals, and ground connections, creating high resistance that triggers P0690.
• Extreme Cold: Extreme cold causes older relays to become mechanically sticky, delaying de-energization and tricking the PCM into reading high voltage.
• Extreme Heat: High under-hood temperatures increase electrical resistance, pushing marginal circuits (corroded terminals or failing relays) over the failure threshold.

How to Talk to a Mechanic About This Code

Say this: "I have a P0690 code indicating high voltage on the PCM power relay sense circuit. Please start by testing the PCM relay, its socket, and related wiring for shorts or corrosion before considering a PCM replacement."

Directs the technician to the most common and least expensive causes first (relay, wiring) and discourages jumping to a costly PCM replacement.

Avoid saying:

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

Questions to ask before authorizing the repair:

• Did you test the PCM power relay itself? What were the results?
• Did you check for battery voltage on the sense circuit at the PCM connector, and what was the reading?
• Can you show me the damaged wire or corroded connector you found?
• Before replacing the module (PCM, TIPM, IPDM), can you confirm you ruled out all external circuit faults?
• What is the warranty on the proposed repair, including parts and labor?

Where to Take It: Dealer vs Independent vs Chain

• Dealer: Recommended only if the fault is a known TSB or requires module replacement and programming.
  Best for: Vehicles under warranty., Repairs related to specific TSBs (like the Ford Fuse 27 issue)., Complex module replacements (PCM, TIPM, IPDM) requiring manufacturer-specific programming.
  Downsides: Highest labor rates., Quick to replace entire modules rather than attempting nuanced wiring repairs. (Typical cost: +50% vs. baseline)
• Independent Shop: Best fit for most P0690 scenarios. A good independent shop performs necessary circuit tests efficiently without defaulting to the most expensive part.
  Best for: Out-of-warranty vehicles., Diagnosing common electrical faults like bad relays, corroded grounds, or chafed wiring., Finding an auto-electric specialist for intermittent problems.
  Downsides: Diagnostic capabilities vary widely. Vet the shop's electrical expertise., May lack specialized tools to program a new PCM. (Typical cost: +0% vs. baseline)
• Chain Shop: AVOID for P0690 diagnosis. They are not equipped for the circuit tracing required to properly diagnose this code.
  Best for: Simple maintenance like oil changes or tires.
  Downsides: Technicians lack advanced electrical diagnostic training., High pressure to sell parts leads to incorrect recommendations, like suggesting a new PCM without testing. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the estimated repair cost for a major component (like a PCM or TIPM) exceeds 50% of your car's private-party value, pause and consider your options.

• Car worth $4000, fix is $2200: Walk away. The repair cost is over half the car's value. Sell as-is or to a junk buyer.
• Car worth $15000, fix is $1200: Fix it. The repair cost is well below the 50% threshold and is a reasonable investment.
• Car worth $2500, fix is $700: Borderline. Consider the car's overall condition. If it needs other repairs soon, sell it. If reliable, fix it.

What Scan Tool You Need for This Code

Minimum: A basic OBD-II code reader to read and clear codes. A multimeter is the primary diagnostic tool, but a scanner is needed to reset the light.

A simple reader only confirms P0690. Advanced scanners with bidirectional control command the PCM relay on and off, allowing real-time circuit testing.

Budget: MOTOPOWER MP69033 / Ancel AD310 (~$25) — Reads and clears P0690. Displays freeze-frame data to show the vehicle's state when the fault occurred. Cannot perform advanced tests.

Mid-range: BlueDriver Pro / Thinkdiag2 (~$120) — Offers full system scanning and live data graphing. Some offer limited bidirectional controls to command the PCM relay on/off.

Professional: Autel MaxiCOM MK900 / Foxwell NT809BT (~$500-700) — Provides full bidirectional control to actively test the PCM relay and circuit, dramatically speeding up diagnosis.

Rent vs buy: For a one-time diagnosis, use a free auto parts store scan to confirm P0690 before testing with a multimeter. Buy a scanner only if you regularly repair cars.

How to Clear the Code After You Fix It

1. Fix the underlying electrical fault (replace relay, repair wire).
2. Reconnect the battery if disconnected.
3. Use an OBD-II scan tool to clear P0690 and related codes.
4. Perform a complete drive cycle to reset readiness monitors.

Drive cycle (~30 minutes): A generic drive cycle requires a cold start (sitting 8+ hours), 3 minutes of idling with electrical loads on, 15 minutes of steady highway driving (55 mph), and 20 minutes of mixed city stop-and-go driving.

Readiness monitors affected: Comprehensive Component Monitor, Misfire Monitor, Catalyst Monitor, Evaporative System Monitor

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

Watch out for:

• Clearing the code without fixing the root cause guarantees immediate return.
• Disconnecting the battery clears the code but resets all readiness monitors, causing an automatic emissions test failure.
• Failing to drive under the correct conditions prevents OBD-II readiness monitors from setting to 'Ready'.

Will This Fail Emissions / State Inspection?

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

• California: An illuminated Check Engine Light causes an automatic smog check failure. All readiness monitors must be 'Ready' after repairs.
• New York: An active P0690 code causes an automatic NYS DMV inspection failure. Registration renewal is blocked until repaired.
• Texas: Active P0690 codes fail emissions testing in required counties. Texas allows only one 'Not Ready' monitor on 2001+ vehicles.

Most Commonly Affected Vehicles

• Ford F-150 (2009-2014) — Frequently appears with fuel system codes (P025A, U0109) due to an overheated fuel pump fuse (Fuse 27). TSB 15-0137 requires a fuse relocation kit to fix the overheating issue.
• Chevrolet / GMC Silverado, Sierra, Tahoe, Suburban (2007-2014) — Wiring harnesses chafe and short out near the A/C accumulator or frame rails. Loose ground wires at the frame are also common. Often appears with P1682.
• Dodge / Chrysler / Jeep Ram, Grand Cherokee, Charger (2007-2015) — Caused by a faulty relay soldered inside the Totally Integrated Power Module (TIPM). Requires specialized repair or full TIPM replacement.
• Nissan Titan, Frontier, Altima (2004-2023) — Points to a failure of the Intelligent Power Distribution Module (IPDM), which contains integrated, non-serviceable relays vulnerable to water intrusion.
• Hyundai / Kia Elantra, Sonata, Optima (2005-2023) — Traced to a faulty main ECM relay or corrosion within the under-hood fuse box.
• Volkswagen Jetta, Golf, Passat (2005-2023) — Caused by a faulty power supply relay (labeled 'J271', 'J329', Relay 433, or 100) or wiring issues near the main fuse panel.
• Subaru Outback, Forester, Impreza (2005-2023) — Traced to a faulty main relay or a failing alternator diode leaking AC voltage into the DC system.
• Mercedes-Benz Various (2000-2020) — Points to a failing power relay, wiring issue, or water damage in the front Signal Acquisition and Actuation Module (SAM).

Manufacturer-Specific Notes

• Ford: On 2009-2014 F-150s, P0690 is caused by an overheating 20A fuel pump fuse (F27). TSB 15-0137 dictates installing a kit to relocate this fuse to a larger, robust circuit.
• General Motors (Chevrolet/GMC): GM truck wiring harnesses rub against the A/C accumulator and frame rails, causing chafed wires and shorts that trigger P0690 and P1682.
• Chrysler/Dodge/Jeep: Uses a Totally Integrated Power Module (TIPM) with internal, non-replaceable relays soldered to a circuit board. P0690 often requires replacing the entire TIPM assembly.
• Nissan: The internal ECM relay is permanently integrated into the Intelligent Power Distribution Module (IPDM) circuit board. Water intrusion requires replacing the entire IPDM.

Real Owner Stories

2012 Ford F-150 with 140K miles

While pulling a trailer at 65 mph, the engine died for 15 seconds, then restarted with flashing warning lights. The owner took it to a dealer.

What they tried:

1. The dealer tested the battery, which passed.
2. A mechanic inspected the under-hood fuse box for a known issue.
3. Found the 20A fuel pump fuse (Fuse 27) burnt and melted, matching TSB 15-0137.

Outcome: The dealer installed the TSB fuse relocation kit ($20 part) to move the circuit. Total repair cost was $350.

Lesson: On 2009-2014 F-150s, sudden stalling or P0690 points directly to the Fuse 27 issue. Inspecting this fuse first saves diagnostic time. The relocation kit is a $20 DIY fix.

2010 Chevy Silverado with intermittent no-start

The truck intermittently cranked but wouldn't start. P0690 was present.

What they tried:

1. Owner swapped the PCM relay with the horn relay, but the problem persisted.
2. Inspected battery terminals and ground wires, finding no issues.
3. A shop diagnosed a faulty PCM and quoted $1,200.

Outcome: A second auto-electric mechanic found a chafed wiring harness near the A/C accumulator shorting the PCM power wire to ground. Repairing the wires cost $250 and permanently fixed the truck.

Lesson: Never accept a costly PCM replacement without a second opinion. Intermittent electrical issues are usually wiring problems. GM trucks frequently suffer harness chafing in the engine bay.

2013 Dodge Grand Caravan with multiple electrical issues

Vehicle presented P0690, flickering headlights, random radio shut-offs, and low-speed stalling.

What they tried:

1. Owner replaced the battery, which failed to solve the problem.
2. A mechanic replaced the PCM power relay, but symptoms returned the next day.

Outcome: The issue was traced to a failing Totally Integrated Power Module (TIPM). The internal relays are soldered and non-replaceable. The entire TIPM was replaced with a remanufactured unit for $700, resolving all faults.

Lesson: On Chrysler-family vehicles, P0690 accompanied by erratic electrical behavior points to the TIPM. You cannot replace a single relay; the entire module requires replacement.

How to Prevent This Code From Triggering

• Clean battery terminals and check ground straps (Every 12 months or during oil change) — Corrosion creates unwanted resistance, leading to unstable voltage that triggers P0690 and stresses sensitive modules.
• Apply dielectric grease to fuse/relay box connectors (As needed in salt-belt or high-humidity regions) — Dielectric grease seals out moisture, preventing corrosion on metal contacts and ensuring stable electrical connections.
• Replace the main battery on a schedule (Every 3-5 years) — Aging batteries fail to provide stable voltage during cranking, causing spikes or drops that confuse the PCM.
• Ensure aftermarket accessories are professionally installed (During installation) — Professional installers use dedicated circuits to isolate new accessories, preventing voltage feedback that triggers P0690.

Frequently Asked Questions

What is the biggest mistake people make when diagnosing P0690?

The most common mistake is replacing the expensive PCM without testing the circuit. Because the PCM reports the code, people assume it's broken. The fault is almost always an external $20 relay, corroded wire, or bad ground.

Can I just splice a damaged wire to fix this?

Yes, you can repair a damaged wire using a weatherproof butt connector with heat-shrink insulation or by soldering and sealing it. Twisting wires and using electrical tape is unreliable and will fail. Proper splicing restores the circuit permanently.

Can aftermarket parts like a remote starter cause P0690?

Yes, improperly tapping an aftermarket accessory into the PCM's power or ignition circuits creates voltage feedback. This tricks the PCM into detecting a high voltage condition. Inspect the wiring of recently installed alarms or stereos first.

What is an ECM/PCM power relay?

It is a small electro-mechanical switch controlling the flow of high-current battery power to the main computer. It uses a low-current signal from the ignition switch to close a high-current contact. This powers the computer and protects it from surges.

Can a bad battery cause a P0690 code?

While weak batteries typically cause low voltage codes, loose terminals or internal battery failure cause erratic voltage spikes. Ensure you have a healthy, fully charged battery with clean connections before diagnosing complex codes. A healthy battery reads 12.6 volts at rest.

Will clearing the code make it go away?

You can clear the code with a scanner, but it returns immediately if the underlying electrical fault remains. Clearing the code only erases the fault memory. It does not repair the stuck relay or shorted wire.

Can P0690 cause transmission problems?

Yes, because the PCM controls transmission functions, unstable power causes erratic shifting or forces the transmission into 'limp mode'. Fixing the primary P0690 power issue resolves these secondary transmission symptoms.

Key Takeaways

• Code P0690 triggers when the Powertrain Control Module (PCM) detects constant battery voltage (12.6V+) on its power relay sense circuit when it expects 0V.
• A faulty, stuck-closed PCM power relay in the under-hood fuse box causes over 70% of P0690 codes and costs under $30 to replace.
• Driving with P0690 risks sudden engine stalling at highway speeds or a complete no-start condition.
• Never replace the $800+ PCM without first performing a $0 relay swap test with the horn or A/C relay.
• On 2009-2014 Ford F-150s, an overheating fuel pump fuse (Fuse 27) frequently triggers P0690, requiring a $20 TSB relocation kit.