B1688
Lamp Dome Input Circuit Short To Ground
Body Chassis/Safety Lighting circuit short 🟢 Low — Fix at next service
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What This Actually Means
In plain language — no jargon

The dome light input wire is touching ground, creating a short circuit that prevents the ECU from properly reading the dome light switch signal. It's like a light switch wire touching a metal frame instead of completing its normal circuit.

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Symptoms You May Notice
3 known symptoms for this code
Dome light stays on or off regardless of door opening
Interior lighting control malfunction
Body control module warning light illuminated
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors the dome light input circuit voltage to detect when doors open or the dome light switch is activated. It expects a high voltage signal when the circuit is open and a low voltage when activated. A short to ground keeps the signal grounded, preventing the ECU from distinguishing between on and off states.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Dome Light Input Voltage 12V (open) to 0V (activated) Constant 0V (grounded short)
Circuit Resistance High impedance when open Less than 5 ohms to ground
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Wiring harness inspection
Visually trace the dome light circuit from the switch to the body control module for pinched, abraded, or exposed wires touching ground.
2
Dome light switch assembly
Replace the dome light switch if internal wiring is shorted or contacts are damaged.
3
Body control module connector
Disconnect and inspect the BCM connector pins for corrosion or water intrusion causing the short.