Rear Wiper Motor Speed Sensor Circuit Failure
Diagnostic trouble code B1894 indicates a fault in the rear wiper motor speed detection circuit. This code sets when the body control module (BCM) does not receive the expected signal from the speed sensor integrated into the rear wiper motor, preventing the system from verifying the motor's operational status or actual speed. Per SAE J2012, 'B' codes refer to body-related faults, and this one is manufacturer-specific.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty rear wiper motor with internal speed sensor failure
- Open or short circuit in the speed detection wiring
- Corroded, damaged, or loose electrical connector
- Defective body control module (BCM)
3. Symptoms You Will Notice
- Rear wiper does not operate or operates erratically
- Rear wiper may not park in the correct position
- Check engine or service wiper warning light illuminated
4. Step-by-Step Diagnosis
Scan for B1894 and any related codes, then clear and retest
Inspect the rear wiper motor connector for corrosion, damage, or poor contact
Test the speed sensor circuit wiring for continuity, shorts, and proper voltage
If wiring and connector are good, replace the rear wiper motor assembly
If problem persists, test or replace the BCM
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is safe to drive, but the rear wiper may not function properly, which can reduce visibility in rain or snow.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on whether the wiper motor or BCM needs replacement and labor rates.