What Does B1594 Mean?
This code indicates the Body Control Module (BCM) has detected a short to ground in the autolamp delay decrease circuit. The autolamp system automatically controls exterior lighting based on ambient light conditions, and the delay decrease function allows adjustment of how long lights remain on after the vehicle is turned off. The BCM detected that voltage in this control circuit dropped to ground level when it should have been at a higher reference voltage.
Common Causes
45%
Damaged or chafed wiring harness causing short to ground in the autolamp delay circuit
30%
Faulty autolamp delay switch or control module internal short
15%
Corroded or moisture-damaged connector pins creating ground path
10%
Failed Body Control Module with internal circuit fault
Diagnostic Steps
1
Step 1: Perform visual inspection of the headlight switch assembly and autolamp delay switch for physical damage, burnt contacts, or moisture intrusion. Check all associated connectors for corrosion, pushed-out pins, or damaged terminals.
2
Step 2: Disconnect the autolamp delay switch or headlight switch assembly connector. Using a digital multimeter, measure resistance between the delay decrease circuit terminal and ground with the switch disconnected. Reading should be infinite ohms (open circuit). If reading shows continuity to ground, wiring harness has a short.
3
Step 3: If wiring shows continuity to ground with switch disconnected, isolate the short by disconnecting the BCM connector for the autolamp circuit. Measure resistance again between the circuit wire and ground at various points along the harness to locate the short using the process of elimination.
4
Step 4: If wiring tests good, reconnect harness and back-probe the delay decrease circuit at the switch connector with ignition on. Voltage should read battery voltage or BCM reference voltage (typically 5V or 12V depending on system design). If voltage is present, replace the faulty switch assembly.
5
Step 5: Clear the code and operate the autolamp delay function through its full range. Monitor live data for proper circuit voltage changes. Verify code does not return and delay function operates correctly.
Estimated Repair Cost
$100 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a short to ground in the autolamp delay decrease circuit. The autolamp system automatically controls exterior lighting based on ambient light conditions, and the delay decrease function allows adjustment of how long lights remain on afte...
The most common cause of B1594 (Autolamp Delay Decrease Circuit Short To Ground) is: Damaged or chafed wiring harness causing short to ground in the autolamp delay circuit
Typical repair costs for B1594 range from $100 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving as this only affects the convenience feature of delayed headlight shut-off after exiting the vehicle. Headlights will still function normally for driving, but the automatic delay feature may not work properly. Repair at earliest convenience to restore full lighting system functionality.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1594 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Body
System
Exterior Lighting Control System
Difficulty
Type
Manufacturer
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
