B1785

Code

Other B — Body

Mirror Passenger Up Circuit Short To Ground

Brand: Other

Type: B — Body

Views: UK: 20 EN: 33 RU: 19

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Page language: EN

Causes

Damaged/shorted wiring harness (insulation chafing, pinched wire)
Short to ground inside the passenger mirror assembly (motor or internal wiring)
Corroded/contaminated connector or terminal at mirror or body harness
Faulty mirror motor or internal switch causing internal short
Faulty body control module (BCM) or mirror control module output (less common)
Water ingress or foreign debris in mirror housing causing short

Symptoms

Passenger mirror will not move up (or will not move properly)
Intermittent mirror operation or mirror stuck in one position
DTC B1785 present and may return after clearing codes
Possible other mirror-related DTCs or multiple circuits affected if harness damaged

What to check

Retrieve freeze-frame and full DTC list with a scan tool, confirm B1785 is current
Visually inspect passenger mirror, door harness, and connectors for damage, corrosion, or water entry
Operate mirror Up/Down/Left/Right while observing behavior and any related symptoms
Check for other stored body module codes that might indicate a harness or BCM issue

Signal parameters

Normal inactive state: control line should be high-impedance or at battery voltage depending on vehicle (typically >9 V)
When commanded Up: control line changes state to drive the motor (voltage depends on vehicle design)
Short to ground condition: measured voltage near 0 V and low resistance to chassis ground
Expected resistance from control pin to ground when circuit healthy: high (kΩ range); short: near 0 Ω

Diagnostic algorithm

Read and record all DTCs, freeze frame data and active/inactive status with a scan tool. Clear codes and attempt to re-create the fault.
Visually inspect passenger mirror assembly, door hinge area and harness for broken wires, pinches, or corrosion. Pay attention to areas that flex when the door opens.
Operate mirror function while watching harness and connector, perform a wiggle test from dash switch to mirror to see if fault is reproduced.
Disconnect passenger mirror connector, then attempt to operate the mirror Up command while scanning. If the code clears or the condition changes, suspect mirror assembly or connector. If code remains, suspect wiring/BCM side.
With IGN on (and vehicle safe), measure voltage at the mirror control pin for the UP circuit with respect to chassis ground while commanding Up. Record voltages. Low/near 0 V when it should be high indicates short to ground.
Measure resistance between the UP control pin and chassis ground with harness disconnected. Low resistance indicates a short to ground in harness or mirror.
If harness short suspected, backprobe and isolate sections: disconnect intermediate connectors (door jamb, bulkhead) and repeat resistance/voltage checks to locate segment with short.
If mirror assembly determined faulty, replace mirror and verify operation and that DTC does not return.
If wiring and mirror are good, test the BCM/mirror control module output per factory procedure. Replace module only after confirming output failure and ruling out harness/connector/mirror faults.
After repair, clear codes, test mirror operation through full range, and confirm B1785 does not return.