B1816 — Wiper Rear Motor Down Relay Coil Circuit Short To Battery

B1816 — Wiper Rear Motor Down Relay Coil Circuit Short To Battery. A fault in the ignition system. Short, gentle driving to a shop is usually possible. Typical causes: worn spark plugs or wrong plug gap, damaged coil wiring or connector, failed ignition coil or coil pack.

body electrical

Is it safe to drive?

Drive with caution 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.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm B1816 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many B0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the ignition system for damage, corrosion, chafing or poor contact.
Subsystem check Swap the coil to another cylinder and see if the fault code follows it.
Subsystem check Inspect spark plugs for wear, oil or carbon tracks and check plug gaps.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm B1816 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for B1816 (parts and labor, USD, independent shop rates): Replace spark plugs: $90–$250; Replace an ignition coil: $150–$380; Repair coil wiring or connector: $80–$250. Overall, fixing B1816 usually costs between $80 and $380. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

How do I diagnose B1816 myself?

Start with a scan: confirm B1816, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the ignition system, and verify the suspect component against live data before buying parts.

Is it safe to drive with B1816?

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.

How much does it cost to fix B1816?

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

What is the most common cause of B1816?

The most common causes are: worn spark plugs or wrong plug gap, damaged coil wiring or connector, failed ignition coil or coil pack.

What does OBD2 code B1816 mean?

The B1816 diagnostic trouble code relates to a fault inside the body electrical control system, specifically involving the rear wiper motor down relay coil circuit and a short to battery condition. In plain terms, the vehicle's control module has detected that the relay coil responsible for moving the rear wiper in the downward direction is receiving an unexpected voltage signal — either direct battery power or an unregulated feed that should not be present in that circuit. The ECU runs this check repeatedly during normal operation. When two or more consecutive drive cycles show the circuit reading outside its expected voltage window, the module stores B1816 and illuminates the associated warning indicator.

When this code sets, the freeze frame data recorded alongside it captures the engine's operating conditions at the exact moment the fault was detected: engine speed, load percentage, coolant temperature, and vehicle speed. That snapshot is the most useful starting point for any diagnosis, because it tells you what the vehicle was doing when the module noticed the problem. Rather than guessing, you can replicate those conditions and watch the live data to see where the short is occurring. The rear wiper itself may continue to operate in a limited fashion, or it may stop responding to commands entirely, depending on how the module has responded to protect the circuit.

Symptoms of B1816

Rear wiper fails to operate or moves in one direction only
Wiper motor draws excessive current, blowing fuses repeatedly
Check Engine, body, or dedicated wiper warning light is illuminated
Intermittent wiper operation without a clear pattern
Visible damage or corrosion on the rear wiper motor connector or wiring harness
Other body control functions operating oddly due to shared circuit involvement

What causes B1816?

Short circuit in the wiper motor down relay coil wiring between the module and motor
Corroded, bent, or broken terminals inside the wiper motor connector
Faulty rear wiper motor with an internal short to the coil circuit
Failed body control module programming or output stage damage
Chafed wiring harness insulation near the rear hatch or tailgate hinge area
Aftermarket accessory installation that tapped into the wiper relay circuit incorrectly
Water intrusion into the wiper motor housing creating a short path to ground

How to diagnose B1816

Scan the vehicle with a compatible OBD2 tool, confirm that B1816 is present in the body or chassis control module, and record all stored freeze frame data and any related codes. Related codes in the B1xxx range often point to shared power supplies or ground paths that compound the problem.
Access manufacturer technical service bulletins for your specific make, model, and model year. Search the NHTSA database or the manufacturer's owner site using your VIN to identify any known campaigns or software updates related to B1816.
Visually inspect the entire rear wiper motor circuit: the motor itself, the relay coil wiring running from the body module, the ground path, and every connector in between. Pay close attention to the harness routing near the rear hatch hinge, where flexing and wear are common.
With a multimeter, check the voltage at the wiper motor connector while the system is commanded on. A reading above specification or presence of battery voltage on a circuit that should carry only a switched ground confirms the short-to-battery condition.
Disconnect the wiper motor and test the circuit again. If the fault clears, the motor itself is the source of the short. If the code persists, the wiring harness is the culprit.
Clear B1816, run a complete drive cycle that recreates the freeze frame conditions, and verify the code does not return before releasing the vehicle.

Repair options and costs

Depending on which component caused the short, here are typical repair solutions and their costs at independent shop rates in the United States:

Repair damaged wiring harness or replace corroded connector terminals: $80–$250
Replace the rear wiper motor assembly: $120–$300
Replace or reprogram the body control module if the output stage is damaged: $250–$600

Always begin with the least expensive option — inspecting and repairing wiring — before replacing the motor or the control module. Most B1816 faults trace back to damaged harness insulation or corroded connectors, particularly on vehicles where the rear hatch wiring endures repeated flex cycles.

Total cost to fix B1816

The total bill for resolving B1816 typically falls between $80 and $600, depending on the root cause. If the problem is a simple broken wire or corroded connector, expect to pay toward the lower end of that range. Motor replacement and especially module replacement or reprogramming push the cost toward the higher end. An accurate diagnosis before purchasing parts is the single most effective way to keep your total spend on the low side.

Can you drive with B1816?

Drive with caution. B1816 indicates an electrical short in the wiper circuit, which can drain your battery or cause intermittent electrical faults that affect other body functions. If the rear wiper stops working entirely, visibility in poor weather may be reduced — not immediately dangerous, but something to address promptly. There is no risk of catalytic converter damage with this particular fault, but a sustained short circuit left unrepaired can lead to battery failure or, in rare cases, a vehicle no-start condition. Fix it at your earliest convenience, and do not ignore it indefinitely.