B1817 — Wiper Rear Motor Down Relay Coil Circuit Short To Ground

How much does it cost to fix B1817?

Replace spark plugs — $90–$250; Repair coil wiring or connector — $80–$250; Replace an ignition coil — $150–$380. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Is it safe to drive with B1817?

Drive with caution and avoid load. Ignition faults cause misfires that quickly overheat and destroy the catalytic converter; if the Check Engine Light flashes, stop and fix it first.

What does OBD2 code B1817 mean?

B1817 — Wiper Rear Motor Down Relay Coil Circuit Short To Ground. A fault in the ignition system. Short, gentle driving to a shop is usually possible. Typical causes: failed ignition coil or coil pack, worn spark plugs or wrong plug gap, faulty ignition control circuit in the ECM.

What are the symptoms of B1817?

Drivers most often notice: increased fuel consumption, hard starting, especially in damp weather, misfires under load or at idle, Check Engine Light on.

Will B1817 clear itself?

Sometimes B1817 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

When your vehicle's body control module detects that the rear wiper motor's down relay coil circuit is pulling excessive current to ground, it logs OBD2 trouble code B1817. In plain terms, the circuit that commands the rear wiper motor to park itself — the down position — has developed an unwanted short path to ground. The module watches this circuit every time the wipers cycle, and if it sees the voltage or resistance readings fall outside the factory specification, B1817 gets set. That stored fault then triggers the Check Engine or service light to alert you. The code does not appear from a single momentary glitch; the module requires the abnormal condition to repeat under specific operating parameters before it locks the code in place. Captured alongside B1817 is freeze frame data — engine load, vehicle speed, coolant temperature at the moment of failure — which tells you exactly which driving conditions caused the problem and guides your diagnostic path.

The rear wiper system relies on a small relay that energizes the motor's park circuit when you switch the wipers off. That relay coil receives battery voltage through one circuit and is grounded through a control circuit by the body module. When everything works, the module grounds the relay coil briefly, the motor runs the wiper to the parked position, and the circuit opens. A short to ground on the coil side of that circuit bypasses the module's control entirely, creating a condition the module flags as B1817. The issue falls under the body electrical category, not powertrain, which means it will not always cause drivability symptoms — but it can leave the rear wiper in an unpredictable state or drain the battery if the relay stays energized.

Common symptoms of B1817

• Check Engine or dedicated body warning light illuminated on the instrument cluster
• Rear wiper fails to park correctly after use, stopping in any random position instead of the designated park spot
• Rear wiper does not respond at all when activated, or cycles continuously without stopping
• Unusual electrical draw noticed when the vehicle sits unused, potentially leading to a dead battery
• In some cases, no obvious symptom at all beyond the stored code — the module may compensate for the fault
• A ticking or humming noise from the rear hatch area even with the wipers switched off, indicating the relay coil is staying energized

What causes B1817?

• Chafed or pinched wiring harness in the rear hatch or liftgate area, where the wiper motor and relay wiring flex with every open and close cycle
• Moisture intrusion into the rear wiper motor housing or connector, causing the coil circuit to short to the metal body ground
• Corroded or loose connector at the rear wiper motor or the body module that controls it, producing intermittent resistance that falls below threshold
• A failed rear wiper motor relay — the relay coil internally shorting to ground rather than through the control circuit
• Aftermarket alarm, remote start, or other accessory installations that tap into the wiper control circuit and create conflicting signals
• Physical damage to the relay coil wiring from cargo, mounting hardware, or tailgate hinges during routine loading

How to diagnose B1817

1. Connect an OBD2 scanner, confirm B1817 is active or pending, and record all available freeze frame data. Note the vehicle speed, temperature, and load values captured when the fault first occurred — reproduce those conditions during your road test to trigger the fault again.
2. Visually inspect the entire rear wiper motor circuit harness, paying close attention to the boot and connector at the hatch. Look for wire insulation worn through, pinched sections near hinges, and any signs of water entry or corrosion at the motor connector. Wiggle the harness while monitoring the scanner's live data or a multimeter to expose intermittent shorts.
3. Test the relay coil circuit at the motor connector for resistance and for unintended continuity to ground. Compare your readings to the service manual specification — a coil reading that is well below the expected ohms confirms a short.
4. Swap the suspect relay with a known-good unit from the same vehicle type or an identical replacement. If the code moves with the relay, the relay itself is faulty. If the code stays, the wiring or module-side circuit is the culprit.
5. Check manufacturer TSB databases for your specific make and model. Some vehicles have documented wiring harness issues or body module programming updates that resolve B1817 without hardware replacement.
6. Clear B1817 after your inspection and repairs, then complete a full drive cycle including rear wiper operation in wet conditions. Verify the code does not return.

Repair options with costs

• Replace the rear wiper motor relay (individual relay or as part of the motor assembly depending on the model): $40–$120 for the part, plus $50–$90 in labor at independent shop rates, totaling roughly $90–$210.
• Repair chafed or damaged wiring in the hatch circuit: wiring repair or harness replacement runs $80–$250 depending on whether the harness is plug-and-play or requires soldering and loom replacement.
• Replace the rear wiper motor entirely if the motor housing is water-damaged: $100–$220 for the motor plus $50–$110 labor, typically $150–$330 total.

How much does it cost to fix B1817?

The total bill hinges on exactly what is shorting and how accessible the harness is. A straightforward relay replacement is the least expensive scenario — most owners pay between $90 and $210 including parts and labor. If the wiring harness needs repair or replacement, costs climb to $80–$250 depending on the extent of the damage. The most expensive scenario is a full wiper motor replacement at $150–$330. On average across all common repair paths, expect to spend roughly $150–$250 at an independent shop. Getting an accurate diagnosis before purchasing parts is strongly recommended — the cheapest fix is rarely the most obvious one, and you do not want to replace a motor when only a wire is damaged.

Can you drive with B1817?

Drive with caution. B1817 does not typically cause engine drivability issues, but a shorted wiper relay circuit can gradually drain your battery if the coil stays energized, leaving you stranded. In wet weather the loss of rear wiper function reduces rear visibility, which is a safety concern. The fault itself is classified as a caution-level issue — address it before a long trip, and if you notice your battery going dead overnight, have the vehicle inspected before it becomes an emergency.

Related OBD2 codes

• B1800: Lamp Turn Signal Front Output Circuit Short To Battery
• B1801: Lamp Turn Signal Front Output Circuit Short To Ground
• B1802: Lamp Turn Signal Rear Output Circuit Failure
• B1803: Lamp Turn Signal Rear Output Circuit Open
• B1804: Lamp Turn Signal Rear Output Circuit Short To Battery
• B1805: Lamp Turn Signal Rear Output Circuit Short To Ground