OBD-II Code B1375: Ignition Circuit Malfunction (And Manufacturer-Specific Meanings)

What Does B1375 Mean?

Code B1375 is a manufacturer-specific Body Diagnostic Trouble Code (DTC). For Ford and GM, it indicates the Body Control Module (BCM) detects a missing or incorrect voltage signal from the ignition switch. However, major brands like Honda, Acura, and Toyota use this exact code for completely different systems, such as power tailgates or windshield wipers. Verifying the code's definition for your exact make and model is the mandatory first step.

Technical definition: The SAE/ISO definition for B1375 varies by manufacturer. Common definitions include 'Ignition Switch A Circuit Failure' (Ford) or 'Device Ignition 3 Circuit' (GM), indicating a control module lacks expected voltage from an ignition circuit. Alternative official definitions include 'Driver's Side Power Tailgate Switch Circuit Malfunction' (Honda/Acura) and 'Lost Communication with Wiper Sub Motor Assembly' (Toyota). The specific definition dictates the entire diagnostic path.

Can I Drive With B1375?

Yes, But With Caution. You can drive, but it carries risks depending on your vehicle make. If the code relates to the ignition circuit (common on Ford and GM), the engine stalls while driving, creating a major safety hazard. If it relates to a non-critical system like a Honda power tailgate, driving is perfectly safe but the feature remains inoperative.

Common Causes

• Faulty Ignition Switch (Ford/GM) (Very Common) — The internal mechanical contacts wear out, causing intermittent or total signal loss to the BCM. This is the leading cause for vehicles where B1375 relates to the ignition.
• Faulty Component Switch (Honda/Toyota) (Very Common) — For makes like Honda or Acura, the driver's side power tailgate switch itself frequently fails internally, triggering the B1375 code.
• Weak or Failing Battery (Common) — Low system voltage (below 12.4V) causes modules to misinterpret normal signals or drop communication, falsely triggering codes like B1375 during engine cranking.
• Wiring Harness Damage or Corrosion (Common) — Wires in the steering column or leading to the affected component chafe, break, or short to ground. Connectors also corrode from moisture, interrupting the signal.
• Blown Fuse or Faulty Relay (Less Common) — A fuse or relay protecting the specific circuit (ignition, tailgate, wiper) fails due to a momentary short or age, cutting power to the system.
• Improperly Installed Aftermarket Accessories (Less Common) — Remote starters, alarms, or stereos tapped incorrectly into ignition or accessory circuits alter expected voltage readings and confuse control modules.
• Faulty Control Module (Rare) — The module responsible for interpreting the signal (BCM or Power Tailgate Module) fails internally. Consider this only after proving all wiring, connectors, and switches are functional.

Symptoms

• Engine Stalls Intermittently While Driving — A momentary loss of the 'RUN' signal from a faulty ignition switch shuts the engine off, posing a significant safety risk.
• Car Cranks but Won't Start — If ignition-related, the BCM fails to detect the key in the 'START' position, preventing activation of the starter relay, fuel pump, or ignition coils.
• Power Tailgate Inoperative — On many Honda, Acura, and Nissan vehicles, the tailgate refuses to open or close with the driver's side switch or remote.
• Accessories Shut Off Randomly — Radio, climate controls (HVAC), or dashboard lights fail to turn on or shut off randomly as they lose the 'Accessory' or 'RUN' signal.
• Windshield Wipers Malfunctioning — On certain Toyota models, a communication failure within the wiper motor assembly causes wipers to become inoperative or behave erratically.
• Fault Code Present in BCM (scan-tool only — no driver-felt sign) — The B1375 code is stored in the Body Control Module and is readable with an OBD-II scanner.

Diagnostic Flowchart

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

Common Fixes & Costs

• Replace Ignition Switch — Parts: $40-$150, Labor: $100-$250, ~1.5 hr book time (Intermediate)
• Replace Power Tailgate Switch — Parts: $30-$80, Labor: $50-$100, ~0.8 hr book time (DIY)
• Repair Damaged Wiring or Connector — Parts: $10-$50, Labor: $125-$250, ~2 hr book time (Intermediate)
• Replace Blown Fuse — Parts: $1-$5, Labor: $0, ~0.1 hr book time (DIY)
• Replace Control Module (BCM/Tailgate) — Parts: $300-$800, Labor: $150-$300, ~2.5 hr book time (Professional)

Used vs. New Parts: Buying Guide

When a used part is worth it: For simple, non-wear items like a power tailgate switch, a used OEM part from a salvage yard is cost-effective. The failure mode is rarely due to wear.

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

Donor quality checklist:

• Verify the part number matches exactly.
• Choose donors from dry states to minimize corrosion risk.
• Look for clean connector pins with no signs of heat damage.

Decision logic:

• If The part is a high-failure, wear-prone item like an ignition switch AND the cost of a new aftermarket part is under $50 → Buy new aftermarket. The low cost outweighs the risk of a used part failing again.
• If The vehicle is older than 10 years AND budget is the primary concern → A used OEM switch is an acceptable risk with a 30-day warranty.
• If The part is electronic and requires programming (like a BCM) → Favor new or professionally remanufactured parts. A used module has hidden faults or incompatibility.

Warranty tradeoff: Used parts offer a 30-90 day warranty covering only the part. New aftermarket parts come with a 1-year to limited lifetime warranty. New OEM parts carry a 1-2 year warranty.

Worst-case if a used part fails: $200-$400 if a used part fails after installation, representing repeated labor costs.

What Happens If You Wait — Timeline

1. 0-1 month: Intermittent starting issues or a single random stall. For tailgate/wiper faults, the feature fails once and works again after a key cycle. (MPG impact: 0%% · Added cost: $0)
2. 1-4 months: Stalling becomes frequent. Accessories flicker or shut off when turning. The car fails to start, leaving you stranded. Tailgate/wiper features work less than 50% of the time. (MPG impact: 0-1%% · Added cost: $100-$300 (Towing cost))
3. 4-8 months: The vehicle is unreliable. Repeated failed start attempts cause extra wear on the starter and battery. A parasitic drain weakens the battery overnight. (MPG impact: 1-3%% · Added cost: $300-$600 (Towing plus premature battery/starter failure))
4. 8+ months: Catastrophic failure. The vehicle becomes a permanent no-start. An electrical short damages the Body Control Module (BCM). An engine stall at a critical moment leads to an accident. (MPG impact: N/A% · Added cost: $800-$2000+ (BCM replacement or accident-related costs))

Cost of Not Fixing It

• Immediate: If ignition-related, the vehicle will not start, leaving you stranded. The engine stalls while driving, creating a major safety hazard. (Added cost: $100-$300 (Towing costs))
• 1-6 months: An intermittent ignition fault causes added stress on the starter motor and battery from repeated start attempts. (Added cost: $200-$500 (Premature starter or battery replacement))
• 6+ months: A persistent electrical short damages sensitive control modules like the BCM. An engine stall at high speed leads to an accident. (Added cost: $500-$1500+ (BCM replacement or accident-related costs))

Diagnosis Steps

1. Verify the Code Definition
   Use a professional-grade scan tool to find the exact definition of B1375 for your vehicle's year, make, and model. A B1375 on a Ford F-150 (ignition) is a completely different problem than on a Honda Odyssey (tailgate).
   Tools: OBD-II Scanner with Manufacturer-Specific Definitions (Beginner)
2. Test the Battery and Charging System
   Ensure the battery has a static charge above 12.4V. Perform a load test to confirm its health. Low system voltage causes numerous false electrical codes.
   Tools: Multimeter or Battery Tester (Beginner)
3. Inspect Fuses and Relays
   Consult the owner's manual to locate and inspect all fuses and relays related to the system identified in Step 1. Replace any blown fuses.
   Tools: Owner's Manual, Fuse Puller (Beginner)
4. Scan for All Codes and Check Freeze Frame Data
   Check for any other DTCs. Communication codes (U-codes) provide clues. Freeze frame data shows the vehicle's state when the code was set, isolating the conditions causing the fault.
   Tools: OBD-II Scanner (Beginner)
5. Visually Inspect Wiring and Connectors
   Inspect the relevant components based on the code's definition. Look for chafed wires, melted plastic, or green/white corrosion on connector pins at the steering column or tailgate hinges.
   Tools: Flashlight, Trim Removal Tools (Intermediate)
6. [PRO TIP] Test Ignition Switch Voltage Drop
   Connect a multimeter in voltage mode. Place the red lead on the battery's positive terminal and the black lead on the ignition switch's output wire. Turn the key to RUN. A reading above 0.5V indicates excessive resistance, meaning the switch is failing.
   Tools: Multimeter, Vehicle-Specific Wiring Diagram (Advanced)
7. [PRO TIP] Perform a Wiggle Test
   With the multimeter connected to the suspect circuit, gently wiggle the key in the ignition. Then, wiggle the associated wiring harness. If the voltage reading fluctuates, you found the loose connection or wire break.
   Tools: Multimeter, Wiring Diagram (Advanced)
8. Check for Continuity and Shorts to Ground
   Disconnect the battery and connectors at both ends of the suspect wire. Test for continuity (less than 1 Ohm). Test for a short by placing one lead on the wire and the other on a known good ground (should read OL).
   Tools: Multimeter, Vehicle-Specific Wiring Diagram (Advanced)
9. [ADVANCED] GM Ignition 3 Circuit Voltage Test
   Probe the 'Ignition 3' wire at the HVAC control module connector with a multimeter. A reading below 11V with the key on (engine off) points to a problem with the ignition switch or wiring from the fuse block.
   Tools: Multimeter, Vehicle-Specific Wiring Diagram (Advanced)
10. [ADVANCED] Honda Power Tailgate Switch Continuity Test
    Disconnect the switch connector. There should be no continuity between the terminals when unpressed. When pressed and held, there should be continuity (less than 1.0 Ohm). If it fails either test, replace the switch.
    Tools: Multimeter, Trim Removal Tools (Advanced)
11. [ADVANCED] Toyota Wiper LIN Bus Signal Check
    Check the LIN bus wire at the wiper motor connector with an oscilloscope. A healthy signal is a square wave switching between 0V and 12V. A flat line or distorted waveform indicates a wiring problem or motor failure.
    Tools: Oscilloscope, Vehicle-Specific Wiring Diagram (Advanced)

When This Code Triggers (Freeze-Frame Conditions)

• DTC that caused the frame: B1375 (The primary code that triggered the data snapshot.)
• Key Position: RUN or START (Fault occurs during the key-on or cranking sequence.)
• System Voltage: 9.5V - 11.5V (Code sets during engine cranking when voltage naturally dips with a weak battery.)
• Vehicle Speed: 0 mph (Faults are detected during startup before the vehicle moves.)

Related Codes

• B1376 — Indicates a 'Circuit Short to Battery'. While B1375 is often an open circuit, B1376 points specifically to a wire touching a power source.
• B1377 — Indicates a general failure in the same circuit family. Diagnosing B1377 is identical to B1375, and they frequently appear together.
• U0140 — Lost Communication With Body Control Module. A faulty ignition switch failing to power up the BCM causes this code alongside B1375.
• B1352 — On Honda/Acura, this 'Power Tailgate Control Unit Internal Error' appears with B1375 when the control unit itself fails from water damage.

Climate & Environmental Factors

• Cold Weather: Extreme cold increases the internal resistance of an aging battery, causing voltage to drop low enough to trigger false codes during startup. It also makes plastic wiring insulation brittle and prone to breaking.
• High Humidity / Moisture: Moisture is the primary cause of corrosion on electrical connectors. Water intrusion into the tailgate switch or wiper motor assembly leads to short circuits that trigger the code.

How to Talk to a Mechanic About This Code

Say this: "I have a [Your Vehicle Make] with a B1375 code and the symptom is [Your Symptom]. Based on my research for this specific car, the code points to the [Specific System] circuit. I'd like to book a diagnostic appointment to confirm the fault in that circuit."

This language shows you've done your research and directs the technician to the correct system. It prevents wasting diagnostic time on unrelated parts like the ignition system if you have a Honda.

Avoid saying:

• 'My check engine light is on, can you look at it?' (Too vague and invites an expensive diagnostic process).
• 'Just fix whatever is wrong with it.' (Gives the shop a blank check to replace parts without approval).
• 'My car won't start and it has a B1375 code.' (Misleading if you drive a Honda).

Questions to ask before authorizing the repair:

• Can you explain exactly what test you performed to confirm this part has failed?
• Is the proposed fix a new switch, a wiring repair, or a module? Please provide a detailed cost breakdown.
• If the issue is a bad wire, will you repair the harness or replace the whole thing? What is the cost difference?
• What is the warranty on the parts and the labor for this specific repair?

Where to Take It: Dealer vs Independent vs Chain

• Dealer: Recommended for complex cases (Toyota LIN bus fault) or if the vehicle is under warranty. Otherwise, it is too expensive.
  Best for: Vehicles under warranty or with an open recall., Complex, manufacturer-specific issues like the Toyota LIN bus wiper fault requiring proprietary tools., When you want guaranteed OEM parts.
  Downsides: Significantly higher labor rates and part costs, often 40-50% more than independent shops., Defaults to replacing an entire assembly when a simpler repair is possible. (Typical cost: +40% vs. baseline)
• Independent Shop: Best fit for most B1375 scenarios. A good independent shop specializing in electrical diagnostics handles these faults efficiently and affordably.
  Best for: Out-of-warranty vehicles where cost is a factor., Common, well-documented B1375 variants like the GM ignition switch or Honda tailgate switch., Building a long-term relationship with a mechanic.
  Downsides: Quality varies widely; you must vet the shop based on reviews and ASE certifications., Lacks the latest diagnostic tools for brand-new models. (Typical cost: +0% vs. baseline)
• Chain Shop: AVOID for diagnosing B1375. The varied nature of this code requires diagnostic expertise not found at chain shops.
  Best for: Simple, routine maintenance like oil changes, tires, and batteries.
  Downsides: Not recommended for complex electrical diagnostics., Technician skill is inconsistent, with high pressure to upsell unnecessary services., Lacks deep diagnostic tools for non-standard codes like B1375. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the estimated repair cost exceeds 40-50% of the car's current private-party value, seriously consider selling it as-is or trading it in.

• Car worth $4000, fix is $2000: Walk Away. A repair cost of 50% of the car's value is too high. Put this money toward a replacement vehicle.
• Car worth $12000, fix is $1800: Fix It. The repair cost is 15% of the vehicle's value, making it a financially sound repair.
• Car worth $2500, fix is $350: Fix It. The repair for a faulty switch is 14% of the car's value, a reasonable cost to restore reliability.

What Scan Tool You Need for This Code

Minimum: A scanner that reads manufacturer-specific Body Trouble Codes (B-codes). A basic $20 reader only shows generic 'P' codes and will NOT see B1375.

B1375 has different meanings for Ford, Honda, and Toyota. You need a scanner that identifies the code's specific definition for your vehicle to know if you are chasing an ignition, tailgate, or wiper problem.

Professional: Autel MaxiCOM MK808S or Launch X431 CRP919XBT (~$450-600) — Offers dealer-level diagnostics, full bidirectional control, and access to all modules. Allows a technician to command the BCM and test individual circuits.

Rent vs buy: Auto parts stores have loaner tool programs, but verify their scanners read manufacturer-specific 'B' codes. If you do your own repairs, buying a tool like the BlueDriver Pro is a worthwhile investment.

How to Clear the Code After You Fix It

1. Reconnect battery if disconnected for repair.
2. Use an OBD-II scan tool to clear the Diagnostic Trouble Code from the Body Control Module (BCM).
3. Perform the specific system function test (e.g., cycle the ignition key, operate the power tailgate switch) to confirm the fix.
4. Perform a drive cycle to allow vehicle readiness monitors to reset.

Drive cycle (~20 minutes): A specific drive cycle is not required for a B-code. The code clears and stays cleared after the repair and a few successful key cycles. For full system readiness after a battery disconnect: Cold start, let idle for 3 minutes. Drive a mix of city and highway for 20 minutes.

Readiness monitors affected: Disconnecting the battery resets all engine and emissions readiness monitors (Catalyst, O2 Sensor, EVAP).

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

Watch out for:

• Clearing the code without fixing the electrical fault results in the code returning immediately.
• Forgetting to check for related U-codes that point to the real root cause.
• Disconnecting the battery causes a failed emissions test until a full drive cycle is completed.

Will This Fail Emissions / State Inspection?

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

• California: If B1375 illuminates the Check Engine Light, it causes an automatic failure. If the battery was disconnected, all readiness monitors must be set to 'Ready' before passing.
• New York: An illuminated Check Engine Light is an automatic failure of the emissions inspection.
• Texas: In counties requiring emissions testing, an illuminated Check Engine Light results in an automatic failure.

Most Commonly Affected Vehicles

• Ford F-150, Explorer, Focus (1998-2015) — Often related to a faulty ignition switch or a wiring issue in the steering column. Ford uses suffixes (e.g., B1375-13 'Circuit Open') to aid diagnosis.
• Chevrolet / GMC Silverado / Sierra, Tahoe / Suburban (2003-2014) — Commonly defined as 'Device Ignition 3 Circuit', pointing to the HVAC control module not receiving the proper RUN signal from the ignition switch.
• Honda / Acura Odyssey, Pilot, MDX (2011-2018) — Exclusively defined as 'Driver's Side PTG Switch Circuit Malfunction'. The issue is a faulty switch or water in the power tailgate control unit.
• Toyota Various with Rain-Sensing Wipers (2005-2020) — Defined as 'Lost Communication with Wiper Sub Motor Assembly'. Requires checking the LIN bus signal with an oscilloscope.
• Nissan Murano, Pathfinder, Quest (2003-2014) — Indicates a fault in the power tailgate system, typically related to the switch or control unit.
• SAAB 9-5 (2006-2009) — Set if the radio detects an incorrect value from the ignition circuit, causing the radio to shut down after one hour.
• Isuzu Hi-Lander (1998-2004) — Refers to 'Oil Change Lamp Circuit Open', indicating a problem with the instrument cluster light or wiring.
• Hyundai / Kia Various (2010-2022) — Verify the definition carefully. Always check for Technical Service Bulletins (TSBs) for software updates resolving erroneous codes.

Manufacturer-Specific Notes

• Ford: Ford's use of suffixes (e.g., B1375-11 for 'Circuit Short To Ground', B1375-13 for 'Circuit Open') tells the technician exactly whether to look for a grounded wire or a broken one.
• General Motors (Chevrolet/GMC): The 'Ignition 3' circuit specifically powers the HVAC head unit. If the climate controls are dead and B1375 is present, the ignition switch is the prime suspect.
• Honda / Acura: B1375 is consistently and exclusively used for the 'Driver's Side Power Tailgate Switch Circuit'. Technicians should never diagnose a no-start condition based on this code for a Honda.
• Toyota: B1375 points to a LIN Bus communication failure between the main wiper motor and the secondary 'sub motor' assembly, requiring an oscilloscope for diagnosis.

Real Owner Stories

2012 Honda Odyssey with 115K miles

Power tailgate suddenly stopped working from all buttons. The van beeped, but the tailgate wouldn't move. No other symptoms were present.

What they tried:

1. Checked fuses related to the power tailgate; all were good.
2. Disconnected the battery for 30 minutes to reset the modules; the problem persisted.
3. Removed the driver's side rear interior trim panel to access the Power Tailgate Control Unit.

Outcome: The owner found corrosion on a connector pin due to water intrusion from a known body seam leak. Cleaning the connector with electrical contact cleaner restored normal tailgate function. Sealing the body seam prevented recurrence.

Lesson: On Honda/Acura vehicles, B1375 is almost always a tailgate issue. Inspect the control unit behind the driver's side rear trim for water damage before replacing expensive parts.

2005 Chevrolet Silverado 1500 at 150K miles

The truck intermittently failed to start (no crank, no click). The HVAC climate controls also randomly shut off while driving.

What they tried:

1. Replaced the battery and starter, which did not solve the problem.
2. Researched forums and found B1375 points to the 'Ignition 3' circuit powering the HVAC module.

Outcome: Replacing the electronic ignition switch inside the steering column (Part: ACDelco D1462G) resolved both the no-start condition and the HVAC issue.

Lesson: On GM trucks, B1375 links to the ignition switch and causes seemingly unrelated electrical issues like dead climate controls. An intermittent no-start combined with random electrical faults strongly points to a failing ignition switch.

2010 Ford F-150 with 105K miles

The truck cranked but would not start randomly over several months. A quick spray of starting fluid got it to fire up.

What they tried:

1. Suspected a fuel delivery problem.
2. Scanned for codes and checked for TSBs related to a 'crank no start' condition, finding TSB 15-0137.

Outcome: The TSB described the 20A fuel pump fuse (Fuse 27) overheating and melting its contacts. The owner found the fuse and slot burnt. Installing a TSB-specified fuse relocation kit (Part No. EL3Z-14293-A) permanently solved the issue.

Lesson: A 'crank, no start' issue isn't always the ignition switch or fuel pump. On Fords, an overheating fuel pump fuse mimics a failing pump. Always check for TSBs for your specific symptoms.

1992 Toyota Pickup with wiper issues

Windshield wipers stopped working. After replacing a blown fuse, the wipers would not turn off at all.

What they tried:

1. Swapped the wiper motor with a junkyard part, but the problem remained.
2. Suspected the wiper control switch on the steering column.

Outcome: A short circuit within the wiper control switch assembly allowed constant power to the motor. Replacing the wiper switch assembly resolved the issue.

Lesson: For Toyota's B1375, if a replacement fuse causes the component to run constantly, it is a classic sign of a shorted switch or relay, not the motor itself.

How to Prevent This Code From Triggering

• Remove excess weight from your keychain. (Daily habit) — Heavy keychains put constant strain on the internal tumblers and the electronic ignition switch behind the lock cylinder, accelerating wear and premature failure.
• Apply dielectric grease to critical connectors. (During any related repair) — Applying a small amount of dielectric grease to the pins seals out moisture and oxygen, preventing the corrosion that causes intermittent signals.
• Inspect and secure wiring harnesses. (Every 30,000 miles) — Ensure wiring looms are properly secured and not rubbing against sharp metal edges or moving parts like the steering column to prevent chafing.
• Keep vehicle interiors and cargo areas dry. (After rain or car washes) — Address any known leaks from body seams or window seals immediately. A dry interior prevents corrosion of sensitive control modules located behind trim panels.

Frequently Asked Questions

What is the biggest mistake when diagnosing B1375?

The single biggest mistake is assuming the code means an ignition problem without verifying its definition for your specific vehicle. You will waste hours diagnosing a no-start on a Honda when the code actually points to the power tailgate.

Can a bad battery cause code B1375?

Yes. A weak battery causes system voltage to drop significantly during engine cranking. Control modules misinterpret this low voltage as a circuit fault, storing false codes like B1375.

My fan only works on high speed, is this related to B1375?

On some GM trucks, a faulty ignition switch fails to power the HVAC module, triggering B1375. However, a fan working only on high speed is the classic symptom of a failed blower motor resistor, a separate issue. A burnt wiring connector at the resistor often causes these multiple failures.

How much does it cost to diagnose code B1375?

Most repair shops charge a diagnostic fee equivalent to 1 to 1.5 hours of labor. This typically ranges from $125 to $250. This fee covers the testing required to accurately identify the root cause.

Is replacing an ignition switch a DIY job?

Experienced DIYers can replace an ignition switch by removing the plastic steering column covers. However, you must navigate around sensitive airbag wiring and anti-theft components. Many modern cars also require a professional scan tool to program the new switch before the engine will start.

What's the difference between an ignition switch and an ignition lock cylinder?

The lock cylinder is the mechanical tumbler you insert your physical key into. The ignition switch is the electronic component behind it that reads the key's position and sends voltage signals to the car's computers.

Will clearing the code fix the problem?

No. Clearing the code with a scanner only turns off the warning light temporarily. The code returns immediately on the next key cycle because the control module still detects the active electrical fault.

Key Takeaways

• Verify the B1375 definition for your specific make before buying parts; it means an ignition fault on a Ford but a power tailgate failure on a Honda.
• Test your battery voltage first, as a drop below 12.4V during engine cranking frequently triggers false B1375 codes across all makes.
• Replace the ignition switch on GM and Ford trucks if the engine stalls while driving or the HVAC controls die, costing roughly $140 to $400 at an independent shop.
• Inspect the power tailgate control unit behind the driver's side rear trim for water corrosion if you own a 2011-2018 Honda Odyssey with this code.