What Does B1789 Mean?
This diagnostic trouble code indicates that the Body Control Module (BCM) has detected a short to ground in the electrical circuit controlling the downward movement of the passenger side mirror. The BCM monitors the mirror motor circuits and has identified that current is flowing through an unintended path to ground in the down position circuit, causing abnormal voltage readings. This prevents proper operation of the passenger mirror's downward adjustment function.
Common Causes
45%
Damaged or chafed wiring in the door harness causing the down circuit wire to contact ground, typically at the door hinge area where flexing occurs
30%
Failed passenger mirror motor assembly with internal short to ground in the downward movement coil windings
15%
Corroded or moisture-damaged mirror connector causing short circuit between down circuit pin and ground pin
10%
Faulty mirror control switch assembly with internal short in the down position contacts
Diagnostic Steps
1
Step 1: Perform visual inspection of the passenger mirror wiring harness, particularly at the door hinge area and mirror base. Look for chafed, pinched, or damaged insulation, exposed copper wire, or signs of water intrusion at connectors. Check mirror connector for corrosion, pushed-back pins, or moisture.
2
Step 2: Disconnect the passenger mirror electrical connector. Using a digital multimeter set to ohms, measure resistance between the mirror down circuit wire (at the vehicle harness side) and chassis ground. Reading should be infinite (open circuit). If continuity to ground exists, trace and repair the short in the door harness or BCM wiring.
3
Step 3: If harness tests good, connect the multimeter to the mirror motor connector terminals corresponding to the down function. Measure resistance between the down motor terminal and mirror housing ground. Resistance should be within manufacturer specification (typically 3-8 ohms). Near-zero resistance indicates shorted motor windings requiring mirror replacement.
4
Step 4: If mirror motor tests within specification, reconnect mirror and disconnect the mirror control switch. Test resistance from the down circuit pin at the switch connector to ground with switch in various positions. Any continuity in neutral or other positions indicates faulty switch requiring replacement.
5
Step 5: Clear the DTC code, reconnect all components, and operate the mirror through all positions multiple times. Monitor live data for down circuit voltage and current draw. Verify code does not return and mirror operates normally in all directions to confirm repair.
Estimated Repair Cost
$100 - $450
Parts + labor, varies by vehicle and location
This diagnostic trouble code indicates that the Body Control Module (BCM) has detected a short to ground in the electrical circuit controlling the downward movement of the passenger side mirror. The BCM monitors the mirror motor circuits and has identified that current is flowing through an unintend...
The most common cause of B1789 (Mirror Passenger Down Circuit Short To Ground) is: Damaged or chafed wiring in the door harness causing the down circuit wire to contact ground, typically at the door hinge area where flexing occurs
Typical repair costs for B1789 range from $100 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This is safe to drive as it only affects the passenger mirror adjustment function and does not impact vehicle control or safety systems. Repair can be scheduled at convenience, though reduced mirror adjustability may affect parking and lane change visibility.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1789 to identify the root cause.
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Quick Info
Category
Body
System
Body Control and Convenience Systems
Difficulty
Type
Manufacturer
Recommended Tools
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