What Does B1894 Mean?
This code indicates the Body Control Module (BCM) has detected a malfunction in the rear wiper motor speed sense circuit. The BCM monitors the feedback signal from the rear wiper motor to verify proper operation and speed control, but is receiving no signal, an intermittent signal, or a signal outside normal parameters. This affects the rear window wiper system's ability to function properly or at all.
Common Causes
40%
Failed rear wiper motor with internal speed sensor or commutator wear preventing proper feedback signal
30%
Damaged, corroded, or loose wiring harness connections between rear wiper motor and BCM
20%
Corroded or damaged rear wiper motor ground connection causing improper circuit operation
10%
Failed Body Control Module unable to properly monitor or interpret speed sense circuit signals
Diagnostic Steps
1
Step 1: Perform visual inspection of rear wiper motor, harness connector, and wiring for physical damage, corrosion, water intrusion, or loose connections. Check for proper sealing of rear hatch/liftgate grommet where wiring passes through.
2
Step 2: Using a digital multimeter, verify power and ground at the rear wiper motor connector with key on and wiper activated. Expect battery voltage on power feed and less than 0.5V on ground circuit.
3
Step 3: Backprobe the speed sense circuit wire at the motor connector while operating the wiper at different speeds. Monitor for pulsed DC voltage signal (typically 0-5V or 0-12V square wave) that changes frequency with wiper speed using multimeter or oscilloscope.
4
Step 4: If no speed signal is present but motor operates, remove and bench test the rear wiper motor with direct power application while monitoring the speed sense output terminal for proper signal generation.
5
Step 5: If speed signal is present at motor but not reaching BCM, check continuity and resistance of speed sense circuit wire from motor connector to BCM connector. Expect less than 5 ohms resistance with all connectors disconnected.
6
Step 6: After repairs, clear code, operate rear wiper through all speed settings for 2-3 minutes, and verify code does not return and proper wiper operation is restored.
Estimated Repair Cost
$150 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a malfunction in the rear wiper motor speed sense circuit. The BCM monitors the feedback signal from the rear wiper motor to verify proper operation and speed control, but is receiving no signal, an intermittent signal, or a signal outsi...
The most common cause of B1894 (Wiper Rear Motor Speed Sense Circuit Failure) is: Failed rear wiper motor with internal speed sensor or commutator wear preventing proper feedback signal
Typical repair costs for B1894 range from $150 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving as this only affects rear window visibility enhancement. Repair at convenience unless driving in conditions where rear visibility through the window is critical for safety.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1894 to identify the root cause.
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Quick Info
Category
Body
System
Body Systems - Rear Wiper/Washer
Difficulty
Type
Manufacturer
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