What Does B1788 Mean?
This code indicates the Body Control Module (BCM) has detected a short to battery voltage in the electrical circuit controlling the downward movement of the passenger side power mirror. The BCM has identified that the mirror down control circuit is receiving constant voltage when it should not be, suggesting a wire is contacting a power source or an internal component failure has created an unintended power path.
Common Causes
40%
Chafed or damaged wiring in the door harness where insulation has worn through and exposed wire contacts battery voltage source
30%
Failed mirror motor assembly with internal short circuit creating path to battery voltage
20%
Faulty mirror control switch with internal short causing constant voltage feed to down circuit
10%
Water intrusion or corrosion in door connector creating voltage cross-feed between circuits
Diagnostic Steps
1
Step 1: Perform visual inspection of passenger door wiring harness focusing on door hinge area and mirror connector for chafed insulation, pinched wires, or damaged connectors. Check for signs of water intrusion or corrosion at all connectors.
2
Step 2: Disconnect the passenger mirror electrical connector and use a digital multimeter to measure voltage on the mirror down control wire at the vehicle harness side (BCM side) with ignition on. Should read 0V with switch inactive; battery voltage present confirms short is in vehicle harness, not mirror.
3
Step 3: If voltage is present at harness, disconnect door jamb connector and retest. If voltage disappears, short is in door harness between jamb and mirror. If voltage remains, short is in main harness between BCM and door jamb connector.
4
Step 4: If no voltage present in Step 2, reconnect mirror and disconnect mirror switch. Measure resistance between mirror down control wire and battery positive at mirror connector. Less than 5 ohms indicates failed mirror motor with internal short to power.
5
Step 5: Repair identified short circuit by replacing damaged wire section, mirror motor assembly, or switch module as determined by testing. Clear codes and verify mirror operates correctly in all directions without code return.
Estimated Repair Cost
$150 - $650
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a short to battery voltage in the electrical circuit controlling the downward movement of the passenger side power mirror. The BCM has identified that the mirror down control circuit is receiving constant voltage when it should not be, s...
The most common cause of B1788 (Mirror Passenger Down Circuit Short To Battery) is: Chafed or damaged wiring in the door harness where insulation has worn through and exposed wire contacts battery voltage source
Typical repair costs for B1788 range from $150 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving as this does not affect vehicle operation or safety systems. The passenger mirror may not adjust properly or may drain battery if motor runs continuously, but immediate repair is not urgent for safety.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1788 to identify the root cause.
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Quick Info
Category
Body
System
Body Electrical System
Difficulty
Type
Manufacturer
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