Code Definition

B1688 — Lamp Dome Input Circuit Short To Ground

System: Body  |  Type: Manufacturer-Specific  |  Make: Ford

About B1688

B1688 is a manufacturer-specific body diagnostic trouble code recorded for Ford vehicles. It belongs to the B-prefix family of codes, which covers body, interior, airbag, or comfort-electronics faults.

When B1688 is stored, the module has detected a short-circuit (voltage pulled to ground or to supply) in the monitored circuit.

Scanning & clearing: Body (B) codes are often stored in the body control module, airbag module, or climate module. A basic OBD-II tool usually will not read body codes — an enhanced or OEM-level scan tool is typically required.

B1688 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The Body Control Module (BCM) or Generic Electronic Module (GEM) monitors the dome lamp input circuit, which carries the signal from the manual dome lamp switch and the door jamb switches that command the interior dome lamp. DTC B1688 is set when the BCM detects that the dome lamp input circuit is shorted to ground, meaning the input pin is being pulled low and held there regardless of switch position. Many dome lamp input circuits are ground side switched, so the BCM normally sees a brief ground signal only when a door is opened or the manual switch is operated, but a short to ground holds th...

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