What Does B1818 Mean?
This code indicates the Body Control Module (BCM) has detected an electrical fault in the relay coil circuit that controls the rear wiper motor's upward or operating position. The BCM monitors the relay coil for proper resistance and current flow, and has identified either an open circuit, short circuit, or excessive resistance preventing proper relay activation. This affects the rear wiper system's ability to function correctly.
Common Causes
40%
Failed rear wiper motor relay with open or shorted coil windings
30%
Damaged wiring harness or corroded connectors between BCM and rear wiper relay
20%
Failed Body Control Module with internal relay driver circuit damage
10%
Blown fuse or fusible link in rear wiper relay coil power supply circuit
Diagnostic Steps
1
Step 1: Locate the rear wiper motor relay (typically in underhood fuse box or integrated power module) and perform visual inspection for corrosion, burnt contacts, or physical damage. Check relay socket for corrosion or pushed-back terminals.
2
Step 2: Using a digital multimeter, measure resistance across the relay coil terminals (typically pins 85 and 86). Normal reading should be 70-120 ohms. Infinite resistance indicates open coil; zero resistance indicates shorted coil.
3
Step 3: With relay removed, check for battery voltage at the relay coil power supply terminal using multimeter. Then verify ground circuit continuity from BCM to relay coil ground terminal (should be less than 1 ohm resistance).
4
Step 4: If relay and circuits test good, use multimeter to check BCM output pin voltage while commanding relay ON with scan tool bidirectional controls. Should see switching voltage (0V to 12V). No voltage change indicates BCM driver failure.
5
Step 5: Install known-good relay and clear codes. Operate rear wiper through all modes and monitor for code return. If code returns immediately with good relay, suspect BCM internal fault or wiring short to ground/power.
Estimated Repair Cost
$75 - $650
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected an electrical fault in the relay coil circuit that controls the rear wiper motor's upward or operating position. The BCM monitors the relay coil for proper resistance and current flow, and has identified either an open circuit, short cir...
The most common cause of B1818 (Wiper Rear Motor Up Relay Coil Circuit Failure) is: Failed rear wiper motor relay with open or shorted coil windings
Typical repair costs for B1818 range from $75 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive as this only affects rear window visibility in inclement weather. Repair at convenience, though sooner repair recommended if rear visibility is frequently needed for safe operation.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1818 to identify the root cause.
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Quick Info
Category
Body
System
Body Electrical System - Rear Wiper
Difficulty
Type
Manufacturer
Recommended Tools
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