What Does B1693 Mean?
B1693 indicates the Body Control Module (BCM) has detected a fault in the automatic headlamp system circuit, specifically the circuit that controls the 'on' function when ambient light decreases. The BCM monitors the autolamp photocell sensor and relay circuit for proper voltage and continuity, and has detected an abnormal condition preventing the automatic headlamp feature from engaging properly. This affects the vehicle's exterior lighting system automation but typically does not prevent manual headlamp operation.
Common Causes
35%
Faulty autolamp photocell sensor or ambient light sensor with internal failure or moisture contamination
30%
Damaged or corroded wiring harness between BCM and autolamp sensor, including broken wires or poor ground connections
20%
Failed autolamp relay or headlamp control relay with internal contact failure
15%
Defective Body Control Module with internal circuit failure or software corruption
Diagnostic Steps
1
Step 1: Perform visual inspection of the autolamp sensor (typically located on dashboard near windshield or in rearview mirror assembly) for physical damage, cracks, or moisture intrusion. Check all visible wiring harness connections for corrosion, bent pins, or loose connections.
2
Step 2: Using a digital multimeter, test the autolamp sensor power supply and ground circuits. Verify the sensor receives proper voltage (typically 5V or 12V reference depending on manufacturer) and has solid ground with resistance less than 1 ohm.
3
Step 3: Monitor live data through the scan tool to observe autolamp sensor voltage output while covering and uncovering the sensor. Normal operation should show voltage changes corresponding to light level changes (typically 0.5V-4.5V range). If no change occurs, sensor is faulty.
4
Step 4: Test autolamp relay operation by commanding the relay on/off through bidirectional controls in the scan tool (if available). Listen for relay click and measure voltage at relay output. If relay does not activate or shows no output voltage, replace relay.
5
Step 5: Inspect wiring harness continuity between BCM connector and autolamp sensor connector using multimeter resistance measurements. Compare readings to manufacturer specifications (should be less than 5 ohms). Check for short to ground or short to power conditions.
6
Step 6: After repairs, clear the code and perform functional test by covering the sensor in a well-lit environment to verify automatic headlamp activation. Road test during dusk conditions to confirm proper system operation and verify code does not return.
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
B1693 indicates the Body Control Module (BCM) has detected a fault in the automatic headlamp system circuit, specifically the circuit that controls the 'on' function when ambient light decreases. The BCM monitors the autolamp photocell sensor and relay circuit for proper voltage and continuity, and ...
The most common cause of B1693 (Autolamp On Circuit Failure) is: Faulty autolamp photocell sensor or ambient light sensor with internal failure or moisture contamination
Typical repair costs for B1693 range from $75 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving as manual headlamp control typically remains functional. However, the automatic headlamp feature will not work, requiring driver to manually activate headlights which could result in driving without lights in low-light conditions if forgotten.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1693 to identify the root cause.
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Quick Info
Category
Body
System
Body Control and Exterior Lighting System
Difficulty
Type
Manufacturer
Recommended Tools
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