B1818 — Wiper Rear Motor Up Relay Coil Circuit Failure #

Note: The code description may differ depending on the vehicle manufacturer (OEM). Below are known description variations:

• Ford: Rear Wiper Motor Relay Coil Circuit Failure
• Chrysler: Rear Wiper Motor Relay Circuit Malfunction
• Toyota: Rear Wiper Relay Up Circuit Open or Short

Code summary for B1818 #

The B1818 diagnostic trouble code (DTC) indicates a detected malfunction in the electrical circuit controlling the rear wiper motor relay coil. This relay is responsible for sending power to the motor that moves the rear windshield wiper upward. When the vehicle’s onboard diagnostics (OBD-II/EOBD) system senses abnormal voltage, resistance, or continuity in this circuit, it triggers the B1818 code. The issue could originate from wiring faults, relay failure, or even a defective wiper motor. While this code primarily affects rear visibility, it rarely impacts vehicle drivability.

Common symptoms for code B1818 #

A B1818 code typically manifests through issues with your rear wiper system. You might notice that the rear wiper does not operate as expected, or it might behave erratically. Here’s what to look for:

• Rear wiper fails to move upward or stops midway
• Unusual clicking noise from the rear of the vehicle when wiper is activated
• Intermittent or non-functional rear wiper operation
• Rear wiper continues to run even when switched off (less common)
• Illuminated check engine or warning light (in some models)

Most likely causes for code B1818 #

Several culprits could trigger the B1818 code, but some are more frequent than others. Ranked by likelihood, the common causes are:

1. Faulty rear wiper relay: The relay coil may have failed, causing an open or short circuit.
2. Damaged or corroded wiring/harness: Broken, frayed, or corroded wires interrupt current flow to the relay and motor.
3. Defective rear wiper motor: An internal short or open in the motor can affect the relay circuit.
4. Blown fuse: A fuse protecting the rear wiper circuit may have failed, sometimes due to a deeper electrical issue.
5. Poor ground connection: Weak or rusty grounds disrupt the electrical path, confusing the control module.
6. Faulty body control module (BCM): In rare cases, the electronic controller managing the wiper circuit fails.

Step-by-step diagnosis for B1818 #

Proper diagnosis ensures you address the real issue, not just the symptoms. Here’s a recommended approach:

• 1. Scan for stored codes: Use an OBD-II/EOBD scanner to confirm the B1818 code and check for related codes.
• 2. Inspect fuse and relay: Locate the rear wiper fuse and relay, test the fuse for continuity, and swap the relay if possible.
• 3. Visual inspection of wiring: Check all visible wiring and connectors between the relay, wiper motor, and BCM for damage or corrosion.
• 4. Test relay coil resistance: Use a multimeter to measure the relay coil’s resistance; compare with manufacturer specs.
• 5. Check ground and power supply: Ensure the circuit has a solid ground and proper voltage at the relay and wiper motor terminals.
• 6. Test rear wiper motor: Bench-test the motor for operation and check for internal shorts or opens.
• 7. BCM check (if needed): If all hardware checks out, consult OEM repair procedures to test the body control module.

Possible repairs for B1818 #

Once you’ve pinpointed the cause, repairs often focus on restoring proper circuit operation. Depending on your findings, you may need to:

• Replace the faulty rear wiper relay
• Repair or replace damaged wiring/connectors
• Install a new rear wiper motor if it fails functional tests
• Replace a blown fuse and resolve underlying shorts
• Clean or repair ground connections
• Replace or reprogram the BCM in rare electronic failure cases

Is it safe to drive with code B1818? #

Yes, but with limitations. The B1818 code will not affect engine operation or core safety systems. However, if you rely on your rear wiper for visibility—especially in rain, snow, or dusty conditions—its failure can compromise your view. If you frequently drive in poor weather or need clear rear visibility (e.g., for towing or reversing), address the issue as soon as possible.

Vehicles most commonly affected by B1818 #

While B1818 can appear on many vehicles equipped with rear wipers, it’s more frequently reported in models where the rear wiper relay and wiring are exposed to moisture or frequent hatch use. Brands with recurrent cases include:

• Ford Escape, Explorer, Edge
• Chrysler Town & Country, Dodge Grand Caravan
• Toyota RAV4, Highlander
• Honda CR-V, Odyssey
• Jeep Grand Cherokee, Liberty

Common mistakes and best practices for B1818 #

Misdiagnosis often leads to wasted time and unnecessary part replacements. Here’s how to avoid pitfalls:

• Don’t replace the wiper motor or relay without confirming the wiring and fuse condition first.
• Always check for water intrusion or corrosion in hatch connectors—especially after heavy rains or car washes.
• Document any other codes or symptoms, as multiple electrical issues can share a root cause.
• Follow a systematic diagnostic process—skipping steps can lead to missed faults.
• Consult OEM wiring diagrams for your vehicle before probing circuits.

Quick FAQ for B1818 #

Q: Will clearing the code fix my rear wiper?

A: No, clearing B1818 may turn off the warning light temporarily, but the issue will recur unless the underlying fault is repaired.

Q: Can a bad relay cause intermittent wiper operation?

A: Yes. A failing relay can cause the rear wiper to work only sometimes, or not at all, depending on internal coil or contact issues.

Q: Do I need special tools to fix this code?

A: Basic tools like a multimeter and screwdriver are often enough for diagnosis. Some repairs may require a scan tool or wiring diagrams, which are available online or from OEM sources.