B1818 — Wiper Rear Motor Up Relay Coil Circuit Failure

OBD2 code B1818 flags a problem with the ignition system (wiper rear motor up relay coil circuit failure). Short, gentle driving to a shop is usually possible. Common culprits: failed ignition coil or coil pack, moisture or oil in the spark plug wells, faulty ignition control circuit in the ECM.

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 B1818 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 B1818 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for B1818 (parts and labor, USD, independent shop rates): Replace an ignition coil: $150–$380; Replace spark plugs: $90–$250; Repair coil wiring or connector: $80–$250. Overall, fixing B1818 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

What is the most common cause of B1818?

The most common causes are: failed ignition coil or coil pack, moisture or oil in the spark plug wells, faulty ignition control circuit in the ECM.

Will B1818 clear itself?

Sometimes B1818 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.

What are the symptoms of B1818?

Drivers most often notice: Check Engine Light on, increased fuel consumption, loss of power and jerking, hard starting, especially in damp weather.

How much does it cost to fix B1818?

Replace an ignition coil — $150–$380; Replace spark plugs — $90–$250; 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.

Is it safe to drive with B1818?

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.

The rear wiper system on many vehicles includes a small electric motor, a relay that controls power delivery, and the wiring between them. Code B1818 specifically points to a problem with the coil inside that rear wiper motor relay — the relay fails to activate the wiper motor properly. When the body control module or powertrain control module tests this circuit and finds the coil either open, shorted, or otherwise unresponsive, it logs B1818.

Modern vehicles verify circuit health through multiple drive cycles before lighting up the dashboard. The module sends a small test signal through the relay coil and expects a specific response. If the reading falls outside acceptable limits across enough consecutive checks, the ECU locks in the fault, saves the conditions at that moment in freeze frame data, and turns on the warning light. That snapshot tells you engine speed, vehicle load, temperature, and road speed when the failure occurred — invaluable when the problem is intermittent.

When B1818 sets, the rear wiper either stops working entirely or operates only in bursts. The driver may notice the wiper doing nothing when activated, or the motor drawing excessive current and blowing fuses repeatedly. In some cases the relay clicks but the motor never spins, pointing to a failed coil inside the relay rather than a dead motor.

Common Symptoms of B1818

Rear wiper fails to operate when switched on
Intermittent wiper operation — works sometimes, then stops
Wiper motor draws excessive amperage and blows fuses
Clicking sound from the relay area without motor movement
Check Engine Light or body system warning lamp illuminated
Stored freeze frame data points to wiper circuit abnormality

What Causes B1818

Failed rear wiper relay with open or shorted coil winding
Corroded or damaged connector at the relay or wiper motor
Broken or chafed wiring in the wiper circuit harness
Wiper motor itself drawing too much current and causing the relay to fail
Water intrusion into the relay box causing short circuits
Faulty body control module sending incorrect commands

How to Diagnose B1818

Connect an OBD2 scanner, confirm B1818 is present, and record all freeze frame data and any related codes. Documenting the exact conditions when the fault set helps reproduce the failure during testing.
Visually inspect the rear wiper relay, its connector, and the wiring running to the wiper motor. Look for corrosion, bent pins, melted insulation, or loose grounds that could cause the circuit to fail.
Test the relay coil resistance with a multimeter — an open circuit or value far outside factory specifications confirms the coil has failed. Compare your reading to the service manual specification for your vehicle.
Check for power and ground at the wiper motor connector while activating the switch. If voltage is present but the motor does not run, the motor itself is likely bad rather than the relay.
Clear the code and perform a test drive that recreates the conditions stored in the freeze frame. If B1818 returns, the fault is confirmed and not intermittent.
Consult manufacturer technical service bulletins for your make and model — some vehicles have known software updates or recall remedies for wiper circuit failures.

Repair Options and Costs

Depending on what the diagnosis reveals, repair costs vary significantly:

Replace rear wiper relay: $50–$180 (parts and labor)
Repair or replace wiper circuit wiring harness: $80–$250
Replace rear wiper motor assembly: $120–$300

Total Cost to Fix B1818

Most B1818 repairs fall in the $50–$300 range depending on which component is at fault. The relay itself is usually the cheapest fix, while wiring harness repairs or motor replacement push costs higher. Labor rates at independent shops typically add $60–$100 per hour. Always diagnose before replacing parts — swapping a good relay when the problem is in the wiring wastes money and leaves the root cause untreated.

Can You Drive with B1818?

Drive with caution. The rear wiper malfunction does not affect engine operation or braking, but reduced visibility in wet conditions creates a safety risk. If the circuit failure causes a short and blows fuses repeatedly, there is a small fire risk from overheated wiring. Address the issue promptly, especially if you frequently drive in rain or if the wiper is required for your vehicle's design.