What Does B1639 Mean?
This code indicates the Body Control Module (BCM) has detected an electrical circuit failure in the passenger side (right side in most markets) mirror control system, specifically the left movement function. The BCM monitors the mirror circuit for proper voltage, resistance, and current flow, and has identified an open circuit, short circuit, or excessive resistance preventing normal operation. This is a manufacturer-specific body code related to power mirror adjustment functionality.
Common Causes
40%
Damaged or broken wiring in the door harness between the BCM and mirror assembly, often caused by repeated door opening/closing flexing the wires
30%
Failed mirror motor or internal mirror switch mechanism within the mirror housing
20%
Corroded or loose electrical connector at the mirror assembly or door junction
10%
Failed BCM internal mirror control circuit or mirror control switch in cabin
Diagnostic Steps
1
Step 1: Visually inspect the door harness boot/grommet area where wiring passes from door frame to door for visible wire damage, chafing, or broken insulation. Check all connectors at the mirror and door junction for corrosion, moisture, or looseness
2
Step 2: Using a multimeter, backprobe the mirror connector while connected and command mirror movement left using the mirror switch. Verify voltage presence (typically 12V) and polarity change when commanding left movement. No voltage indicates wiring/BCM issue; voltage present indicates mirror motor failure
3
Step 3: Disconnect mirror connector and measure resistance across the left motor circuit terminals at the mirror side. Normal reading is typically 3-8 ohms. Open circuit (infinite resistance) confirms motor failure; proper resistance suggests wiring fault between connector and BCM
4
Step 4: If wiring is suspect, perform continuity test from mirror connector back to BCM connector (BCM disconnected) on the left motor circuit wire. Check for shorts to ground or power. Repair any identified wiring faults and verify proper mirror operation after clearing codes
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected an electrical circuit failure in the passenger side (right side in most markets) mirror control system, specifically the left movement function. The BCM monitors the mirror circuit for proper voltage, resistance, and current flow, and ha...
The most common cause of B1639 (Mirror Passenger Left Circuit Failure) is: Damaged or broken wiring in the door harness between the BCM and mirror assembly, often caused by repeated door opening/closing flexing the wires
Typical repair costs for B1639 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 is a convenience feature failure that affects mirror adjustability but does not impact vehicle safety systems. Repair at earliest convenience to maintain proper mirror positioning for visibility.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1639 to identify the root cause.
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Quick Info
Category
Body
System
Body/Comfort Systems
Difficulty
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