What Does B1640 Mean?
This code indicates the Body Control Module (BCM) has detected an open circuit in the passenger side left mirror control system. An open circuit means there is a break in the electrical pathway preventing current flow to the mirror motor or positioning mechanism. The BCM monitors continuity and resistance in the mirror circuit and sets this code when it cannot complete the electrical path for left movement of the passenger mirror.
Common Causes
40%
Broken or corroded wiring in the door harness between door jamb and mirror assembly
30%
Failed passenger side mirror motor assembly or internal circuit board
20%
Faulty mirror switch or driver side mirror control module
10%
Damaged or loose connector at BCM or mirror control module
Diagnostic Steps
1
Step 1: Perform visual inspection of passenger mirror wiring harness through door jamb area, checking for pinched, broken, or chafed wires. Flex the harness while observing for intermittent connectivity issues.
2
Step 2: Using a digital multimeter, check for continuity between the mirror connector pins corresponding to left movement circuit (refer to vehicle-specific wiring diagram). Expected reading should be less than 5 ohms for intact wiring.
3
Step 3: Disconnect passenger mirror connector and measure resistance of the mirror motor left circuit. Compare reading to manufacturer specifications (typically 2-10 ohms). Infinite resistance indicates open motor windings.
4
Step 4: With mirror connector disconnected, backprobe the vehicle harness side while activating left mirror movement from the switch. Verify 12V power supply appears at appropriate terminals. No voltage indicates wiring or switch problem.
5
Step 5: If wiring and power supply are intact, replace passenger mirror assembly. If no power at harness, trace circuit back to mirror switch and BCM, checking all connectors and splice points for corrosion or looseness.
6
Step 6: After repair, clear codes and test mirror operation in all directions. Cycle mirrors through full range of motion 10-15 times to verify proper operation and confirm code does not return.
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 left mirror control system. An open circuit means there is a break in the electrical pathway preventing current flow to the mirror motor or positioning mechanism. The BCM monitors continuity and resi...
The most common cause of B1640 (Mirror Passenger Left Circuit Open) is: Broken or corroded wiring in the door harness between door jamb and mirror assembly
Typical repair costs for B1640 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 as this affects only mirror adjustment functionality, not critical vehicle operation. Repair at convenience, though proper mirror positioning is important for visibility and safe lane changes.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1640 to identify the root cause.
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Quick Info
Category
Body
System
Body Control / Mirror System
Difficulty
Type
Manufacturer
Recommended Tools
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