OBD-II Code B3718: Front Wiper Relay Drive Circuit High / Wiper Park Fault

What Does B3718 Mean?

B3718 is a General Motors-specific Body Diagnostic Trouble Code (DTC). It means the Body Control Module (BCM) cannot determine the 'parked' position of the windshield wipers. The BCM expects a ground signal (near 0 volts) from the wiper motor's internal park switch when the wipers are off. Instead, it detects a high voltage signal (over 1 volt) for more than one second, indicating an open or broken circuit. This blinds the BCM to the wiper position, causing them to stop randomly.

Technical definition: Front Wiper Relay Drive Circuit High. The Body Control Module (BCM) sets this code when the wiper switch is off and it detects a voltage greater than 1.0 volt on the wiper park switch signal circuit for more than one second, when a ground voltage near 0 volts is expected.

Can I Drive With B3718?

⚠️Yes, But With Caution. You can drive the vehicle, but it is a severe safety hazard. Your wipers fail to operate, cycle randomly, or stop mid-windshield, destroying visibility in rain or snow. This condition causes an automatic safety inspection failure in most jurisdictions. Do not ignore this fault.

Common Causes

• Open/Broken Wiper Park Signal Wire (GM Circuit 196) (Very Common) — The most frequent cause, documented in GM TSB #PIT3827D. The yellow wire sending the park signal from the wiper motor to the BCM chafes and breaks. Common failure points are under the electronic brake control module (EBCM) or inside the cabin 8-12 inches from the BCM connector. Rodents frequently chew this specific soy-insulated wire.
🎬 See this guide on how to replace damaged wiring.
• Faulty Wiper Motor Control Module/Cover (Trailblazer/Envoy Platform) (Common) — On GM's GMT360 platform (Chevy Trailblazer, GMC Envoy), the electronic controls and park logic live in a separate pulse board attached to the wiper motor. This module fails frequently and is replaced independently of the motor.
• Faulty Windshield Wiper Motor Assembly (Common) — The internal mechanical park switch within the wiper motor assembly wears out or breaks. Because the switch is not serviced separately, the entire wiper motor assembly requires replacement.
• Poor Ground at Splice Pack G105 (Less Common) — The wiper motor relies on a clean ground connection at splice pack G105 (driver's side engine bay). These GM ground packs corrode heavily, creating high resistance and causing erratic wiper park faults.
• Water Intrusion & Corroded Connectors (Rare) — A degraded windshield cowl seal allows water to leak directly onto the wiper motor assembly. This corrodes the electrical connector pins, interrupting the park signal and mimicking a broken wire.
• Faulty Body Control Module (BCM) (Very Rare) — An internal BCM fault is exceptionally rare. Only consider replacing the BCM after exhaustively testing all wiring, grounds, and the wiper motor assembly.

Symptoms

• Wipers stop in the middle of the windshield — When turned off, the wipers stop immediately in their current position instead of returning to the base of the windshield.
• Wipers cycle on their own at startup — The wipers activate and sweep one to three times when the ignition turns on, even with the switch 'Off', before stopping randomly.
• Wipers will not turn off — On the Trailblazer/Envoy platform, a failing wiper control module causes the wipers to run continuously on a low setting, even when switched off.
• Intermittent or no low-speed operation — Delay and low-speed settings fail completely, while the high-speed setting continues functioning because it bypasses the BCM's park logic.
• Service Vehicle Soon Message — As a Body (B) code, it triggers a 'Service Vehicle Soon' message on the driver information center rather than the main Check Engine Light.

Diagnostic Flowchart

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

Common Fixes & Costs

• Repair Broken Park Signal Wire (Circuit 196) — Parts: $5-$20, Labor: $150-$350, ~2.0 hr book time (Intermediate)
• Replace Wiper Motor Control Module/Cover — Parts: $50-$100, Labor: $80-$150, ~1.0 hr book time (DIY)
  Chevrolet Trailblazer / GMC Envoy: OEM GM 15233297 (Alt: Dorman 601-115, ACDelco 19244883)
• Replace Windshield Wiper Motor Assembly — Parts: $70-$280, Labor: $120-$220, ~1.2 hr book time (DIY)
  Chevrolet Colorado / GMC Canyon: OEM GM 25809218 (Alt: ACDelco 19420523, Cardone 40-3033)
  Hummer H3: OEM GM 10389558 (Alt: ACDelco 19150497, WAI Global WPM7033)
• Clean or Repair Ground Splice Pack G105 — Parts: $0-$5, Labor: $50-$100, ~0.5 hr book time (DIY)
• Replace Body Control Module (BCM) — Parts: $400-$600, Labor: $150-$250, ~2.5 hr book time (Professional)

DIY vs Professional

• Repair Broken Park Signal Wire — Beginner: No
  Tools: Multimeter, wire cutters/strippers, soldering iron, heat shrink tubing, automotive-grade wire.
• Replace Windshield Wiper Motor Assembly — Beginner: Yes
  Tools: Socket set, ratchet, screwdrivers, trim removal tools, wiper arm puller tool.
• Replace Wiper Motor Control Module/Cover — Beginner: Yes
  Tools: Socket set, T20 Torx screwdriver/bit, flathead screwdriver, wiper arm puller tool.
• Clean or Repair Ground Splice Pack G105 — Beginner: Yes
  Tools: Socket set, wire brush, sandpaper, dielectric grease.
• Replace Body Control Module (BCM) — Beginner: No
  Tools: Socket set, trim removal tools.

Used vs. New Parts: Buying Guide

When a used part is worth it: For an older, high-mileage vehicle, a used wiper motor or control module from a reputable auto recycler is a cost-effective repair.

Donor-vehicle mileage cap: roughly under 120000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Verify the exact part number matches your original.
• Avoid parts from flood-damaged cars.
• For Trailblazer/Envoy, ensure the used motor includes a functional control module.
• Inspect the electrical connector pins for corrosion.

Decision logic:

• If Vehicle is over 10 years old and budget is a primary concern → A used part with a 30-90 day warranty is a reasonable choice.
• If The cost of a new aftermarket part is less than 50% more than the used part → Buy the new part for the longer warranty.
• If You are paying a shop for labor → Buy a new part. The risk of paying labor twice if a used part fails outweighs the initial savings.

Warranty tradeoff: Used parts typically include a 30-90 day warranty covering the part only. New aftermarket parts offer 1-year to limited lifetime warranties.

Worst-case if a used part fails: $150-$300 (Paying for a second part plus labor to replace it again)

What Happens If You Wait — Timeline

1. 0-1 month: Wipers stop mid-windshield or cycle once at startup. Code B3718 sets in the BCM. (MPG impact: 0%% · Added cost: $0)
2. Immediate to 6 months: The driver loses visibility in sudden rain or snow storms. The vehicle automatically fails state safety inspections. (MPG impact: 0%% · Added cost: $100-$300 (Traffic ticket for defective safety equipment))
3. 6-12 months: If caused by a chafing harness, vibration causes nearby wires to fail, leading to new DTCs and symptoms. (MPG impact: 0%% · Added cost: $200-$500 (Diagnostic time and repair for newly created wiring faults))
4. 12+ months: If caused by a water leak, prolonged intrusion damages the Body Control Module (BCM), causing a no-start condition. (MPG impact: 0%% · Added cost: $800-$2000 (Cost to diagnose and replace a water-damaged BCM))

Cost of Not Fixing It

• Immediate: Significant safety hazard in poor weather. Vehicle fails state safety inspections. (Added cost: $100-$300 (Potential traffic ticket for non-operational safety equipment))
• 1-6 months: Continued failure and inability to pass inspection. (Added cost: $0)
• 6+ months: If the root cause is a water leak at the cowl, prolonged water intrusion damages the BCM or other nearby electronics. (Added cost: $800-$2000 (Cost to diagnose and replace a water-damaged BCM))

Diagnosis Steps

1. Verify Symptoms and Scan for Codes
   Confirm the wiper parking fault. Use a professional-grade OBD-II scanner capable of reading Body Control Module (BCM) codes to verify B3718 is present. Note any other codes, especially B3715.
   Tools: OBD-II Scanner (BCM capable) (Beginner)
2. Test Park Signal Wire for Continuity
   Disconnect the battery, BCM, and wiper motor connectors. Measure resistance between the yellow wire pin at the BCM and the corresponding pin at the wiper motor. A reading of 'OL' or infinite resistance confirms a broken wire.
   Tools: Multimeter (Intermediate)
3. Perform a Jumper Wire Test
   Run a temporary fused jumper wire between the yellow wire's pin at the BCM and the wiper motor connector. Reconnect the battery and turn the ignition on. If the wipers park correctly, the original wire is broken.
   Tools: Fused jumper wire, basic hand tools (Intermediate)
4. Visually Inspect Wiring Harness
   Check the wiring harness running to the wiper motor for chafing or rodent damage. Focus on the section under the Electronic Brake Control Module (EBCM) in the engine bay.
   Tools: Flashlight (Beginner)
5. Test Park Signal Wire Voltage
   Back-probe the yellow wire at the wiper motor. With ignition on and wipers off, it must read near 0 volts. A steady reading over 1.0V confirms an open circuit.
   Tools: Multimeter, back-probe pins (Intermediate)
6. Inspect and Clean Ground Splice Pack G105
   Locate ground splice pack G105 on the driver's side inner fender. Disassemble and clean all metal contact points with a wire brush until shiny, then reassemble.
   Tools: Socket set, wire brush, sandpaper (Intermediate)
7. Advanced: Scan Tool Live Data Analysis
   Monitor the 'Wiper Park Switch' PID. If it reads 'Inactive' even when wipers are stopped, the BCM is not receiving the ground signal.
   Tools: Professional Bidirectional Scan Tool (Advanced)
8. Advanced: Wiper Park Signal Waveform Analysis
   Visualize the signal on the yellow wire. An open circuit shows a constant high voltage line (5V or 12V) that never drops to ground.
   Tools: Automotive Oscilloscope (Lab Scope) (Advanced)

When This Code Triggers (Freeze-Frame Conditions)

• Ignition Status: ON (Run) (The fault is checked for when the ignition is on.)
• System Voltage: 9.0 - 18.5 Volts (The BCM must have normal operating voltage to run diagnostics.)
• Wiper Switch Command: OFF (The code sets when the BCM expects the wipers to be parked because the switch is off.)
• Park Switch Signal: > 1.0 Volt for > 1 second (The BCM sees a high voltage (open circuit) when it expects to see a ground signal (near 0V).)

Related Codes

• B3715 — Wiper Park Switch Signal Circuit Low. Sets when the BCM sees a short to ground. A chafing wire triggers B3715 intermittently before breaking completely and triggering B3718.
• B3717 — Front Wiper Relay Drive Circuit Low. Sets when the BCM detects low voltage when the relay should be on.
• U0140 — Lost Communication With Body Control Module. Indicates a broader BCM power or ground failure rather than an isolated wiper circuit issue.
• B1001 — Option Configuration Error. Stores in the BCM if it loses communication with the wiper motor park switch.

Climate & Environmental Factors

• Road Salt / High Humidity: Accelerates corrosion on ground points (G105) and connector pins, increasing electrical resistance and triggering the code.
• Extreme Cold: Makes wire insulation brittle. Engine vibration snaps the already-stressed yellow park signal wire.

How to Talk to a Mechanic About This Code

Say this: "I have a B3718 code and my wipers won't park correctly. Based on GM's TSB, it's likely a broken yellow wire in the park circuit. Can you test the continuity of Circuit 196 before quoting a new wiper motor?"

Signals to the shop that you are aware of the common, inexpensive fix. It directs them to perform a continuity check instead of defaulting to an expensive wiper motor replacement.

Avoid saying:

• 'My wipers are acting weird.'
• 'Just fix whatever's wrong with the wipers.'
• 'My buddy said I need a new wiper motor.'

Questions to ask before authorizing the repair:

• Did you perform a continuity test on the yellow park signal wire (Circuit 196)? What was the result?
• If the wire is broken, what is the estimated cost to repair the wire versus replacing the entire harness section?
• If the wire tested good, how did you confirm the wiper motor's park switch failed?
• What is the warranty on the proposed repair, for both parts and labor?

Where to Take It: Dealer vs Independent vs Chain

• Dealer:
  Best for: Vehicles still under warranty., Complex electrical issues requiring proprietary manufacturer diagnostic tools.
  Downsides: Highest labor rates., Dealers often prefer replacing an entire wiring harness rather than performing a cost-effective single-wire repair. (Typical cost: +50% vs. baseline)
• Independent Shop: Best fit. An independent shop with electrical diagnostic experience is ideal. They are more likely to perform the cost-effective wire repair instead of defaulting to a full part replacement.
  Best for: Out-of-warranty vehicles., Common problems with well-documented fixes like B3718.
  Downsides: Quality varies; look for shops with ASE-certified technicians specializing in electrical work. (Typical cost: +0% vs. baseline)
• Chain Shop: Avoid. The risk of a costly misdiagnosis (replacing the motor instead of fixing the wire) is very high.
  Best for: Simple, routine maintenance like oil changes.
  Downsides: Lack in-depth diagnostic tools for specific electrical faults., High pressure to replace parts leads to misdiagnosing this as a bad wiper motor. (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 vehicle as-is.

• Car worth $5000, fix is $600: Fix it. The repair cost is well below the 50% threshold and restores a critical safety function.
• Car worth $3500, fix is $2000: Walk away. A $2000 quote (likely for a new BCM) is over 50% of the car's value.

What Scan Tool You Need for This Code

Minimum: A scanner that reads manufacturer-specific Body (B) codes. Basic engine-only (P-code) readers will NOT see this code.

A standard $20 OBD-II reader only accesses powertrain codes related to the check engine light. Code B3718 is invisible to these basic tools.

Budget: BlueDriver Pro (~$100) — Reads and clears Body (B) codes, shows freeze-frame data, and provides live data from the BCM.

Mid-range: Foxwell NT510 Elite for GM (~$180) — Offers full system diagnostics for GM vehicles and bidirectional control to command the wipers on and off directly from the scanner.

Professional: Autel MaxiCOM MK808 / MK808BT (~$450-550) — Provides full bidirectional control, reads and clears all codes, and displays extensive live data for professional-level diagnostics.

Rent vs buy: For a one-time fix, AutoZone offers loaner scanners capable of reading BCM codes. Buy your own scanner only if you plan to do diagnostics more than once a year.

How to Clear the Code After You Fix It

1. Perform the repair (e.g., fix the broken wire or replace the motor).
2. Reconnect the battery if it was disconnected.
3. Use a BCM-capable OBD-II scan tool to erase the DTCs.
4. Cycle the ignition and test the wipers through all speed settings to confirm they park correctly.

Drive cycle (~5 minutes): A specific drive cycle is not required. After clearing the code, verify the fix by turning the wipers on and off, ensuring they return to the parked position.

Readiness monitors affected: None

Watch out for:

• Disconnecting the battery fails to clear the code from the BCM's memory on modern vehicles.
• The code immediately returns if the underlying electrical fault remains unfixed.
• Basic scanners that only read Powertrain (P) codes cannot see or clear Body (B) codes.

Will This Fail Emissions / State Inspection?

No — by itself this code doesn't fail OBD inspection (but it can keep readiness monitors from setting, which causes a separate fail).

• California: This code does not cause an OBD-II emissions failure. However, inoperative wipers are a safety violation and result in citations.
• New York: The NYS safety inspection explicitly requires windshield wipers to operate and park correctly. Code B3718 causes an automatic failure.
• Texas: While the fault won't cause an emissions failure, law enforcement issues citations for defective safety equipment like non-functional wipers.

Most Commonly Affected Vehicles

• Chevrolet Colorado (2004-2012) — The primary vehicle cited in GM TSB #PIT3827D for the broken yellow park signal wire (Circuit 196).
• GMC Canyon (2004-2012) — Shares the identical wiring harness failure points as the Colorado.
• Hummer H3 (2006-2010) — Built on the GMT355 platform, making it highly susceptible to the broken yellow wire fault.
• Isuzu i-Series (i-280, i-290, i-350, i-370) (2006-2008) — A rebadged Colorado/Canyon sharing the exact same electrical architecture.
• Chevrolet Trailblazer (2002-2009) — Symptoms are caused by a failed Wiper Motor Control Module/Cover (pulse board), not the broken wire.
• GMC Envoy (2002-2009) — Shares the high likelihood of a failed Wiper Motor Control Module/Cover with the Trailblazer.
• Chevrolet SSR (2003-2006) — Experiences identical wiper park symptoms traced back to the motor's internal logic/park switch.
• Chevrolet Equinox (2007-2009) — The BCM only controls the intermittent wiper function. Low and high speeds are wired directly from the switch.

Manufacturer-Specific Notes

• General Motors: Code B3718 is almost exclusive to GM. TSB #PIT3827D pinpoints the yellow wire (Circuit 196) failure on GMT355 platforms.
• Chrysler/Dodge/Jeep: Uses a Totally Integrated Power Module (TIPM) relay instead of a BCM park circuit. Fails similarly but requires TIPM replacement or micro-soldering.
• Ford: Relies on a multifunction switch or integrated motor switch rather than a vulnerable external BCM park wire.

Real Owner Stories

2004 Chevy Colorado - The Classic Misdiagnosis

Wipers cycled 3 times at startup and stopped mid-windshield. Code B3718 was present.

What they tried:

1. Replaced the wiper motor assembly - no change.
2. Replaced the two wiper relays in the fuse box - no change.

Outcome: The owner inspected the wiring harness per TSB #PIT3827. They discovered a severed yellow wire near the firewall. Repairing this single wire completely fixed the problem.

Lesson: Do not replace parts until you test the yellow wire (Circuit 196). A simple continuity test saves the cost of an unneeded wiper motor.

2007 GMC Envoy - The Platform-Specific Fix

Wipers ran continuously on low speed even with the switch 'off'. Code B3718 was stored.

What they tried:

1. Owner suspected the multifunction switch on the steering column.
2. A mechanic checked the wiring harness for breaks but found none.

Outcome: Because the vehicle was an Envoy, the diagnosis shifted to the separate Wiper Motor Control Module/Cover. Replacing the module with an aftermarket Dorman part (601-115) immediately resolved the issue.

Lesson: Platform matters. For Trailblazer/Envoy SUVs, the separate control module is a more likely failure point than the broken wire common on Colorado/Canyon trucks.

2006 Hummer H3 - The Overlooked Ground

Intermittent wiper parking issues. Code B3718 appeared alongside flickering lights.

What they tried:

1. Tested continuity of the yellow wire - it tested good.
2. Replaced the wiper motor assembly, but the problem returned.

Outcome: A technician found heavy corrosion at the G105 ground splice pack. After cleaning all terminals to bare metal, the B3718 code and all electrical issues vanished permanently.

Lesson: A bad ground causes high resistance and erratic signals that the BCM interprets as a component fault. Always check major ground points like G105.

How to Prevent This Code From Triggering

• Periodically Clean Cowl and Wiper Area (Every 3-6 months) — Prevents debris from clogging drain tubes, which causes water to overflow onto the wiper motor and corrode the electrical connector.
• Inspect and Protect Wiring Harness (During any under-hood maintenance) — Visually check the wiper motor harness near the EBCM. Wrap chafed areas with high-temperature cloth tape to prevent wire breaks.
• Clean Engine Bay Ground Points (Every 2-3 years) — Disassembling and cleaning the G105 splice pack prevents corrosion that causes high resistance and unpredictable electrical faults.
• Apply Anti-Corrosion Spray to Connectors (After any disconnection) — Spraying electrical connectors with a corrosion inhibitor repels moisture and prevents pin corrosion.

Frequently Asked Questions

What is the most common mistake when fixing code B3718?

Immediately replacing the wiper motor without testing the yellow park signal wire (Circuit 196). A simple continuity test prevents wasting money on unneeded parts.

What's the difference between code B3718 and B3715?

B3718 means the BCM sees an open circuit (broken wire). B3715 means it sees a short to ground. A chafing wire often triggers both intermittently before failing completely open.

Can a bad ground cause code B3718?

Yes. A corroded ground at GM's G105 splice pack causes high resistance and erratic voltage signals. The BCM interprets this unstable signal as a circuit high fault.

Will replacing the wiper switch on the steering column fix B3718?

No. The fault lies in the circuit reporting the wiper's parked position back to the BCM, not the switch sending the initial 'on' command.

Where exactly is the broken yellow wire usually located?

GM's TSB highlights two hotspots: under the Electronic Brake Control Module (EBCM) in the engine bay, or 8 to 12 inches from the BCM connector inside the cab.

What happens if I don't fix code B3718?

You lose reliable wiper function, creating a severe safety hazard in poor weather. The vehicle automatically fails state safety inspections.

How do I clear code B3718 after the repair?

Use a BCM-capable OBD-II scanner to clear the code immediately. Otherwise, the history code self-clears after 100 successful ignition cycles without the fault returning.

Key Takeaways

• Code B3718 on 2004-2012 GM trucks almost always indicates a broken yellow wire (Circuit 196) between the wiper motor and the BCM.
• Expect the windshield wipers to stop mid-glass or cycle 1 to 3 times at startup when this code triggers.
• Test the yellow park signal wire for continuity before spending $150+ on a new wiper motor, as a $5 wire repair fixes 80% of these cases.
• Replace the $60 Wiper Motor Control Module (pulse board) first if driving a 2002-2009 Trailblazer or Envoy, as this platform rarely suffers from the broken wire issue.
• Fix this fault immediately to avoid failing mandatory state safety inspections and losing visibility during rain or snow.