B1781

Code

Other B — Body

Mirror Driver Down Short To Ground

Brand: Other

Type: B — Body

Views: UK: 27 EN: 40 RU: 33

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Page language: EN

Causes

Short to ground on the mirror down wiring (pinched, chafed or damaged harness)
Corroded or pushed-out connector terminal making unintended contact with ground
Water intrusion in mirror housing or door harness
Failed mirror motor with internal short
Faulty mirror switch or body/control module driver
Aftermarket mirror accessory or recent repair disturbed wiring

Symptoms

Mirror will not move down (may move up/other directions depending on circuit design)
Intermittent mirror operation or stuck mirror
DTC B1781 stored in body/control module
Possible blown fuse or repeated fault history after fuse replacement
Burnt smell or abnormally warm mirror motor in some cases

What to check

Retrieve freeze frame and other mirror-related codes; note voltage states when stored
Visual inspection of door harness, mirror connector and mirror housing for damage, corrosion, or water
Check fuses and any related relays for continuity and correct rating
Backprobe mirror connector while operating switch to observe voltage on Down output
Measure motor coil resistance with connector disconnected to check for internal short to ground
Perform wiggle test on harness while observing signal/voltage and code status

Signal parameters

Battery voltage approx. 12V present at mirror power feed when ignition on
The down driver should switch between ~12V (or open) and ~0V depending on design; unexpected permanent ~0V indicates short to ground
Motor coil resistance typically low (single to low double digit ohms); an extremely low value or near 0 Ω suggests a short
No-load driver output current should rise when commanded; excessive current or immediate drop may indicate short or shorted driver

Diagnostic algorithm

Read and record all mirror/body codes and freeze-frame data. Clear codes and attempt to re-create the fault while observing behavior.
Visually inspect door wiring harness from body hinge to mirror and the mirror connector/housing for chafe, broken insulation, corrosion or water intrusion.
With ignition on, backprobe the mirror connector Down output and operate the mirror Down command. Observe voltage: a constant near 0V when command is not active or when active indicates a short to ground.
Disconnect mirror connector. Measure resistance between the Down output terminal and vehicle ground. A very low resistance (near 0 Ω) indicates a short in wiring or motor.
Measure motor coil resistance across motor terminals; compare to specification if available. Check for short between each motor terminal and the motor housing/ground.
If wiring and motor show no short with connector disconnected, suspect control module driver. Verify by checking output at module harness; if short exists at module pin and not at harness, module replacement or repair may be required.
If short is in wiring or connector, repair or replace damaged sections and connectors. After repair, clear codes and confirm proper operation and that code does not return.
If mirror motor is internally shorted, replace mirror assembly. If control module driver is faulty, follow manufacturer procedures for module replacement/programming.

Likely causes

Wiring rubbed against door hinge, chafed through and contacting body ground
Connector at mirror or door module corroded or terminals shorted
Mirror motor windings internally shorted to motor housing
Short created after a recent door panel removal or mirror replacement
Control module driver transistor failed and is internally shorted to ground

Fault status

⚠️ Status

Control module detected a short to ground on the mirror Down drive circuit (B1781). The Down driver output is at an unexpected low voltage indicating a fault in wiring, connector, motor, or module driver.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-1.5 hours