B1780

Code

Other B — Body

Mirror Driver Down Circuit Short To Battery

Brand: Other

Type: B — Body

Views: UK: 28 EN: 41 RU: 33

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Page language: EN

Causes

Damaged wiring harness (chafing, pinched, exposed conductor) on the mirror down circuit
Corroded or damaged connector at the mirror or control module
Shorted switch or mirror control module (internal short to battery)
Aftermarket accessory or previous repair introduced a short
Faulty mirror actuator/motor with internal short to battery
Blown or incorrect fuse or relay affecting mirror circuit

Symptoms

Passenger or driver mirror will not move down or will not respond correctly
Mirror may move only in one direction or be stuck
Diagnostic trouble code B1780 stored; possible related body/system warning
Intermittent or permanent loss of mirror function
Possible blown fuse or other affected circuits in same fuse/relay

What to check

Read and record freeze frame and associated codes with a scan tool
Visual inspection of mirror, door harness, and connectors for damage, corrosion, or pinched wires
Operate mirror switch while observing behavior and listening for motor activity
Check related fuses and relays for continuity and correct rating
Backprobe mirror connector and switch connector while commanding down to observe voltage
Disconnect mirror connector to see if code clears or behavior changes (module isolated)

Signal parameters

Short condition: steady battery voltage on the down-command circuit (~11–14 V) when circuit should be inactive
Expected (normal) behavior: circuit is either low/grounded or receives a switched drive; not constant battery feed at rest
Mirror motor terminal resistance: low (motor coil resistance, typically a few ohms) — expect continuity but not a direct short to battery/ignition feed
When commanding down, the drive may reverse polarity or apply battery voltage transiently; observe change when switch is operated

Diagnostic algorithm

Connect a scan tool, confirm B1780 and note any related codes, record freeze-frame data
Perform visual inspection: open door, flex harness at hinge, inspect for abrasion, pinching, or connector damage
Operate the mirror switch while observing the mirror harness and connector for obvious movement or shorting
Backprobe the mirror down circuit at the mirror connector with ignition ON and with switch idle: measure voltage to chassis ground. If ~12V present with no command, suspect short to battery upstream
With the connector disconnected at the mirror, check the control module/switch side for presence of battery. If battery is still present, fault is upstream (switch/module or wiring); if it disappears, fault is inside mirror actuator/connector
Perform continuity and insulation checks: with battery disconnected, measure resistance between the down circuit and battery positive to confirm short; measure resistance to ground to check for shorts
Inspect and wiggle the harness while watching the meter/scan tool for intermittent changes (hinge area common failure point)
If wiring and connectors are ok, substitute/replace mirror actuator or control switch as per service manual and re-test
Repair any damaged wiring or connectors using proper splices, seals, and routing; replace faulty modules or actuator if confirmed
Clear codes and perform full function test; road-test and re-scan to ensure code does not return

Likely causes

Pinned/chafed wire contacting battery feed in door harness near hinge
Connector terminal(s) pushed into housing and contacting 12V source
Mirror module or switch internal failure causing battery feed to be present on the down output
Accessory wiring tied into mirror circuit incorrectly

Fault status

⚠️ Status

The body control module detected a short to battery on the mirror driver "down" circuit. The circuit is seeing battery voltage where a switched or grounded signal was expected.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours