What Does B1840 Mean?
B1840 indicates the Body Control Module (BCM) has detected an abnormal electrical condition in the front windshield wiper motor power supply circuit. This code is set when the BCM detects excessive current draw, insufficient current flow, open circuit, short to ground, or short to power in the wiper motor power feed circuit. The BCM continuously monitors the wiper circuit and sets this code when voltage or current values fall outside expected parameters during wiper operation or self-test.
Common Causes
35%
Faulty wiper motor with internal short circuit or seized bearings causing excessive current draw
30%
Damaged or corroded wiring harness, connectors, or terminals in the wiper power circuit between BCM and motor
20%
Blown fuse or faulty wiper relay causing power interruption to the wiper motor circuit
15%
Failed Body Control Module with internal wiper circuit driver failure
Diagnostic Steps
1
Step 1: Visually inspect the wiper motor operation - turn wipers on and listen for abnormal grinding, binding, or humming noises indicating mechanical seizure or motor failure
2
Step 2: Check wiper fuse and relay in the underhood/instrument panel fuse box using a test light or multimeter to verify power supply integrity (fuse should have 12V both sides, relay should click and provide output when activated)
3
Step 3: Using a digital multimeter, backprobe the wiper motor connector with wipers activated to measure voltage (should be 12-14V) and current draw (typically 3-6A normal, 10A+ indicates motor fault)
4
Step 4: Inspect wiper motor connector and harness for corrosion, damaged pins, water intrusion, or broken wires, paying special attention to ground connections which commonly corrode
5
Step 5: Disconnect the wiper motor and perform resistance test across motor terminals (typically 2-5 ohms) and insulation test to ground (should be infinite resistance/open circuit)
6
Step 6: If all components test good, perform BCM output test using scan tool bidirectional controls to activate wiper circuit and monitor current output from BCM driver circuit
Estimated Repair Cost
$100 - $650
Parts + labor, varies by vehicle and location
B1840 indicates the Body Control Module (BCM) has detected an abnormal electrical condition in the front windshield wiper motor power supply circuit. This code is set when the BCM detects excessive current draw, insufficient current flow, open circuit, short to ground, or short to power in the wiper...
The most common cause of B1840 (Wiper Front Power Circuit Failure) is: Faulty wiper motor with internal short circuit or seized bearings causing excessive current draw
Typical repair costs for B1840 range from $100 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is drivable but windshield wipers may be inoperative, creating serious safety hazard during rain, snow, or reduced visibility conditions. Repair should be completed before driving in inclement weather as non-functioning wipers violate traffic laws and significantly increase accident risk.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1840 to identify the root cause.
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Quick Info
Category
Body
System
Wiper/Washer System
Difficulty
Type
Manufacturer
Recommended Tools
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