What Does B1815 Mean?
This code indicates the Body Control Module (BCM) has detected an open circuit in the rear wiper motor down relay coil circuit. The BCM monitors the relay coil control circuit and has identified a break in continuity, preventing the relay from energizing to operate the rear wiper motor in the downward/park position. This is a manufacturer-specific code related to the rear wiper system control circuitry.
Common Causes
35%
Open circuit in wiring harness between BCM and rear wiper relay coil due to chafing, corrosion, or broken wire
30%
Failed rear wiper motor down relay with open coil winding
20%
Corroded or loose connector terminals at relay socket or BCM connector
10%
Failed BCM with internal relay driver circuit fault
5%
Blown fuse in relay coil control circuit
Diagnostic Steps
1
Step 1: Perform visual inspection of rear wiper relay location, check for proper relay installation, corrosion, and verify correct relay type is installed. Remove relay and inspect socket terminals for damage or corrosion.
2
Step 2: Using a digital multimeter, measure resistance across relay coil terminals (typically pins 85 and 86). Normal reading should be 70-120 ohms. Infinite resistance indicates failed relay coil.
3
Step 3: With relay removed, use multimeter to check continuity from relay socket coil control terminal to BCM connector pin (consult wiring diagram). Check both ground and switched power sides of coil circuit for opens.
4
Step 4: Test BCM relay driver output by back-probing the BCM connector at the relay control pin while commanding rear wiper operation. Should see battery voltage switching to ground when activated. If no switching occurs, BCM is likely faulty.
5
Step 5: Inspect wiring harness routing from BCM to rear wiper relay for any signs of chafing, pinching, or damage especially near hinges and body flex points.
6
Step 6: After repairs, clear codes, cycle rear wiper through all functions including park position, and verify code does not return. Monitor relay operation for proper clicking sound during activation.
Estimated Repair Cost
$85 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected an open circuit in the rear wiper motor down relay coil circuit. The BCM monitors the relay coil control circuit and has identified a break in continuity, preventing the relay from energizing to operate the rear wiper motor in the downwa...
The most common cause of B1815 (Wiper Rear Motor Down Relay Coil Circuit Open) is: Open circuit in wiring harness between BCM and rear wiper relay coil due to chafing, corrosion, or broken wire
Typical repair costs for B1815 range from $85 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 during inclement weather. Repair at convenience, though rear wiper functionality will be impaired or non-functional which may reduce rear visibility in rain or snow.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1815 to identify the root cause.
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Quick Info
Category
Body
System
Rear Wiper System
Difficulty
Type
Manufacturer
Recommended Tools
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