What Does B1593 Mean?
This code indicates the Body Control Module (BCM) has detected a short to battery voltage in the autolamp delay decrease circuit. The autolamp system automatically controls exterior lighting based on ambient light conditions and includes a delay feature that keeps headlights on for a set period after the vehicle is turned off. The BCM detected unwanted battery voltage present on the control circuit that should normally operate at a lower voltage or ground reference.
Common Causes
40%
Damaged or chafed wiring in the autolamp delay switch circuit causing direct contact with battery positive voltage
30%
Faulty autolamp delay switch with internal short to power
20%
Corroded or damaged connector pins at the BCM or switch creating cross-circuit short to power
10%
Failed Body Control Module with internal circuit fault
Diagnostic Steps
1
Step 1: Perform visual inspection of the autolamp delay switch, wiring harness from switch to BCM, and all connectors for obvious damage, chafing, melted insulation, or corrosion. Pay special attention to areas where harness passes through firewalls or near sharp metal edges.
2
Step 2: Disconnect the autolamp delay switch connector and use a digital multimeter to measure voltage on the delay decrease circuit pin at the harness side. With ignition on, you should read 0 volts or near ground reference. If battery voltage (12+ volts) is present, there is a short to power in the wiring harness between the switch and BCM.
3
Step 3: If no voltage found in Step 2, check resistance of the delay decrease circuit from the switch connector to the BCM connector with all components disconnected. Reading should be less than 5 ohms for continuity. Then measure resistance between the delay circuit and battery positive; infinite resistance indicates no short, while low resistance confirms a short to power.
4
Step 4: If wiring tests pass, reconnect harness and test the autolamp delay switch itself using a multimeter to verify it does not internally short the circuit to battery voltage when actuated. Replace switch if internal short is confirmed.
5
Step 5: Clear the code, cycle the ignition and autolamp functions, then verify the code does not return. Monitor BCM live data for proper voltage readings on the delay circuit during operation to confirm repair.
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 battery voltage in the autolamp delay decrease circuit. The autolamp system automatically controls exterior lighting based on ambient light conditions and includes a delay feature that keeps headlights on for a set period afte...
The most common cause of B1593 (Autolamp Delay Decrease Circuit Short To Battery) is: Damaged or chafed wiring in the autolamp delay switch circuit causing direct contact with battery positive voltage
Typical repair costs for B1593 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 automatic headlight delay-off feature convenience function. Headlights will still operate normally through manual control, but the delay feature may not function properly or may keep lights on continuously draining the battery.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1593 to identify the root cause.
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Quick Info
Category
Body
System
Body Electrical System - Exterior Lighting Control
Difficulty
Type
Manufacturer
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