B1689 Auto Lamp Delay Circuit Malfunction
The B1689 code indicates that the control module has detected a fault in the auto lamp delay circuit. This system automatically turns the exterior lights on and off based on ambient light conditions and includes a delay function that keeps the lights on for a programmed time after the engine is turned off or when exiting the vehicle. The fault can be caused by a faulty ambient light sensor, a problem with the front control module (FEM) or lighting module, or an issue in the wiring associated with the timing circuit.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty or disconnected ambient light sensor
- Failed front control module (FEM) or lighting module
- Open circuit, short circuit, or corroded connectors in the auto lamp delay wiring
- Damaged auto lamp control relay or switch
- Incorrect configuration or software fault in the control module
3. Symptoms You Will Notice
- Automatic headlights do not turn on or off as expected
- Headlights stay on longer than normal or turn off immediately
- Instrument cluster warning light for exterior lights may illuminate
4. Step-by-Step Diagnosis
Scan for additional codes and verify B1689 is present
Inspect ambient light sensor for damage, dirt, or disconnection; test sensor output
Check wiring and connectors in the auto lamp delay circuit for opens, shorts, or corrosion
Test the auto lamp relay and switch for proper operation
If wiring and components are okay, suspect a faulty FEM or lighting module; perform module self-test or reprogramming
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is generally safe to drive, but automatic headlight function may be impaired. You can manually operate the headlights as needed. Have the issue diagnosed soon to ensure proper lighting.
How much does it cost to fix?▼
Costs vary widely: a new ambient light sensor may cost $50-$150 plus labor; wiring repairs $100-$300; a replacement FEM or lighting module can run $300-$800 plus programming. Total typically $150-$900.