B1786

Code

Other B — Body

Mirror Passenger Down Circuit Failure

Brand: Other

Type: B — Body

Views: UK: 18 EN: 28 RU: 21

AI status

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Page language: EN

Causes

Open or short in passenger mirror down wiring
Poor connector contact or corrosion at mirror or body harness
Faulty passenger-side mirror actuator/motor or internal switch
Faulty mirror control switch or mirror control module/BCM output
Blown fuse or tripped relay supplying the mirror circuit
Water intrusion or physical damage to mirror assembly

Symptoms

Passenger-side mirror will not move down, adjust, or fold as commanded
Mirror may be stuck in one position or move intermittently
DTC B1786 stored in body control module/BCM memory
Possible loss of other mirror functions if shared circuits are affected

What to check

Visual inspection of passenger mirror, housing and wiring for physical damage or water entry
Inspect connectors at mirror and body harness for corrosion, bent pins, or loose fit
Check relevant fuses and relays in the interior/body fuse box
Use scan tool to read live data and attempt an active test of the mirror down function
Backprobe the mirror connector while commanding the function to verify presence of command voltage/pulse and ground
Perform continuity and resistance checks of wiring between BCM/control module and mirror connector

Signal parameters

Supply voltage to mirror circuit: ~battery voltage (approx. 12 V) when supply is present
Command signal from switch/BCM: typically a switched 0 V/12 V or PWM-type drive when commanded — should change state when activated
Ground: low resistance to chassis ground (near 0 Ω)
Actuator resistance: varies by design; open circuit indicates motor or internal wiring failure

Diagnostic algorithm

Retrieve freeze frame and freeze data, record DTC and clear codes. Attempt to reproduce fault by commanding the passenger mirror down function.
Visually inspect mirror and harness; repair any damaged wiring or connectors. Check for water intrusion and corrosion.
Verify fuses/relays related to mirror circuits; replace as needed.
With a scan tool, command the passenger mirror down output and observe live data. Note whether the BCM reports the command and whether the mirror responds.
Backprobe the mirror connector at the body harness while commanding the function: verify supply voltage, command signal, and ground. If no command voltage is present at the harness, suspect switch/module.
If command is present at harness but mirror does not move, disconnect mirror and measure actuator/motor resistance; check for short to ground or open circuit inside mirror.
Repair or replace faulty wiring, connectors, or mirror assembly as indicated. After repairs, clear codes and retest multiple cycles; if fault persists, consider replacing or bench-testing the mirror control module/BCM and re-check system wiring.
After repair, perform a road/test cycle to confirm permanent repair and erase history codes if stable.

Likely causes

Broken or chafed wire between BCM/control module and passenger mirror
Corroded or pushed-out connector pins at mirror or junctions
Defective mirror actuator or internal gearbox/wiring within mirror
Faulty body control module or mirror control output stage
Intermittent connection due to vibration or water contamination

Fault status

⚠️ Status

The passenger-side mirror "down" control circuit is reporting an open, short, or failure to respond to control commands. The BCM has detected abnormal electrical behavior in the circuit.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours