Code
C0161
OPEL
C — Chassis
Brake Light Switch malfunction
Views:
UK: 7
EN: 6
RU: 6
AI status
Completed
Completed
100%
Causes
- Faulty brake light switch (mechanical wear, broken plunger)
- Switch misadjusted or out of position (not making contact when pedal is pressed)
- Corroded or damaged connector or terminals at the switch
- Broken, shorted, or intermittent wiring between switch and control module
- Blown fuse or poor ground in the lighting/control circuit
- Aftermarket modifications or replacement parts incompatible with vehicle
Symptoms
- Brake lights not illuminating or staying on constantly
- ABS/ESP/traction-control warning lamp or message
- Cruise control disengages or will not engage
- Start/shift interlock may prevent engine start or gear selection (if equipped)
- Related functions (charging/regen, hill hold) may be disabled
What to check
- Scan for stored codes and freeze-frame data; note which module set the code
- Visually inspect brake light bulbs and fuses for the lighting circuit
- Operate the brake pedal while observing brake lights and switch movement
- Inspect switch harness and connector for corrosion, bent pins, or water ingress
- Wiggle-test wiring while monitoring the signal with a scan tool or multimeter
- Measure voltage/continuity at the switch and at the control module connector
Signal parameters
- Switch rest (pedal up): circuit open — signal typically 0 V or open-circuit
- Switch active (pedal pressed): circuit closed — signal typically battery voltage (~12 V) or switched ground depending on vehicle
- Continuity when pressed: near 0 Ω; open-circuit when released
- Some vehicles use a 5 V reference and expect a switched 5 V signal to the module
- No high-frequency PWM expected; signal should be steady logically open/closed
Diagnostic algorithm
- Read full set of codes from all modules and record freeze-frame data; note if multiple modules report brake switch fault.
- Verify symptom: have an assistant press the brake pedal while you observe rear brake lamps and the switch plunger movement.
- Visually inspect the switch and its mounting — confirm plunger engages and is aligned with pedal arm; check for damaged plastics or springs.
- Inspect connector: disconnect, check for corrosion, bent pins, secure mating, and water intrusion. Repair or replace connector as needed.
- Check fuses and grounds for the relevant circuits.
- With ignition on, backprobe the switch connector. Verify supply voltage (battery or 5 V ref) and ground. Operate pedal and verify signal changes between supply and ground as expected.
- Check continuity between the switch signal pin and the target module pin. Repair any open/shorts in wiring harness.
- If switch wiring and signals are correct but code persists, substitute a known-good switch or bench-test a new switch before replacing module.
- After repair or replacement, clear codes and re-test drive to confirm fault does not return and related systems (ABS, cruise, lights) operate normally.
- If problem remains with correct signals at the module connector, consider module input circuit fault and refer to module-level diagnostics/service information.
Likely causes
- Brake light switch failed or mechanically stuck
- Connector corrosion or loose terminal at the brake switch
- Switch not properly aligned on the brake pedal
- Open or shorted signal wire between switch and control module
Fault status
Status
Brake light switch malfunction — control module detects invalid, missing or intermittent brake switch input.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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