B1594: Autolamp Delay Decrease Circuit Short to Ground
The B1594 code indicates a short to ground in the autolamp delay decrease circuit. This circuit is responsible for reducing the time the headlights stay on after the vehicle is turned off. When the body control module (BCM) detects an abnormal voltage drop to ground in this circuit, it disables the autolamp delay adjustment function, preventing the driver from shortening the headlight off-delay time.
1. Commonly Affected Makes
2. Most Common Causes
- Short to ground in the autolamp circuit wiring
- Damaged or corroded autolamp switch connector terminals
- Faulty autolamp control switch
- Internal failure of the body control module (BCM)
3. Symptoms You Will Notice
- Inability to adjust the headlight delay time
- Headlights stay on for a fixed period regardless of switch position
- Autolamp system inoperative or erratic behavior
4. Step-by-Step Diagnosis
Scan for B1594 and any related codes
Visually inspect the autolamp switch wiring and connector for damage, corrosion, or shorts to ground
Test the autolamp switch continuity and resistance per manufacturer specifications
Check for voltage and ground signals at the BCM connector related to the autolamp delay circuit
If all else is normal, suspect a faulty BCM and perform further module diagnostics
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, the vehicle is safe to drive. The autolamp delay feature will not work properly, but the headlights will still operate normally when manually controlled.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on whether the issue is a simple wiring repair or requires replacing the autolamp switch or BCM.