What Does B1787 Mean?
This code indicates the Body Control Module (BCM) has detected an open circuit in the passenger side mirror downward tilt motor circuit. The BCM commanded the mirror to tilt downward but detected no current flow or infinite resistance in the circuit, suggesting a break in the wiring, a failed connection, or a defective mirror motor. This prevents the passenger mirror from tilting downward when the adjustment switch is activated.
Common Causes
35%
Broken or corroded wiring between BCM and passenger mirror motor, often at flex points near door hinges
30%
Loose or corroded electrical connector at passenger mirror assembly
25%
Failed passenger mirror motor assembly (down motor winding open)
10%
Faulty BCM internal circuit or relay for mirror down control
Diagnostic Steps
1
Step 1: Visually inspect the passenger mirror connector for corrosion, pushed-back pins, or damage. Disconnect and reconnect the mirror connector while checking for loose fit or terminal issues.
2
Step 2: Using a digital multimeter, backprobe the mirror connector (harness side) and measure resistance on the down motor circuit wire to ground with mirror switch commanded down. Should read 5-50 ohms for a good motor; infinite resistance confirms open circuit.
3
Step 3: Inspect door harness at hinge area for broken or chafed wires by flexing door open and closed while monitoring circuit continuity with multimeter. Check for intermittent opens at flex points.
4
Step 4: If wiring is intact, disconnect mirror assembly and test motor directly by applying 12V to down motor terminals. If motor operates, problem is in vehicle wiring or BCM; if motor does not operate, replace mirror assembly.
5
Step 5: Verify BCM output by measuring voltage at mirror connector (harness side) while commanding mirror down with switch. Should see battery voltage; if no voltage present, trace circuit back to BCM or check BCM replacement.
6
Step 6: After repair, clear codes and cycle mirror through all positions multiple times to verify proper operation and confirm no code returns.
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected an open circuit in the passenger side mirror downward tilt motor circuit. The BCM commanded the mirror to tilt downward but detected no current flow or infinite resistance in the circuit, suggesting a break in the wiring, a failed connec...
The most common cause of B1787 (Mirror Passenger Down Circuit Open) is: Broken or corroded wiring between BCM and passenger mirror motor, often at flex points near door hinges
Typical repair costs for B1787 range from $75 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving. This only affects mirror adjustment convenience and does not impact vehicle safety or operation. Repair at your convenience, though proper mirror positioning is important for visibility.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1787 to identify the root cause.
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Quick Info
Category
Body
System
Body Control and Accessories
Difficulty
Type
Manufacturer
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