What Does B1590 Mean?
This code indicates the Body Control Module (BCM) has detected a short to ground in the autolamp delay increase circuit. The autolamp system automatically controls exterior lighting based on ambient light conditions and has a delay feature that keeps lights on for a set period after vehicle shutdown. The BCM has detected abnormally low voltage or current flowing to ground in the circuit that controls the duration of this delay period.
Common Causes
45%
Damaged or chafed wiring harness causing short to ground in the autolamp delay circuit
30%
Faulty autolamp delay control switch with internal short to ground
15%
Corroded or moisture-damaged connector pins in autolamp circuit creating ground path
10%
Failed Body Control Module with internal circuit fault
Diagnostic Steps
1
Step 1: Perform visual inspection of the autolamp delay switch/headlight switch assembly and associated wiring harness, checking for obvious damage, chafing against metal, pinched wires, or corroded connectors
2
Step 2: Disconnect the autolamp delay switch connector and use a digital multimeter to measure resistance between the delay increase circuit terminal and ground - should read infinite resistance (open circuit). If resistance is low or zero ohms, the switch is faulty
3
Step 3: With switch still disconnected, check resistance from the BCM connector side of the delay increase circuit to ground - should read infinite resistance. If low resistance is found, the wiring harness has a short to ground between the switch and BCM
4
Step 4: Inspect the wiring harness routing from switch to BCM, paying special attention to areas where harness passes through grommets, near metal brackets, or door hinge areas where flexing occurs. Look for abraded insulation or pinch points
5
Step 5: If wiring and switch test good, perform BCM power-down reset and retest. If code returns immediately with no load on circuit, suspect internal BCM fault
6
Step 6: After repair, clear codes, operate autolamp delay function through multiple cycles, and verify code does not return with key-on engine-off and after test drive
Estimated Repair Cost
$100 - $650
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 increase circuit. The autolamp system automatically controls exterior lighting based on ambient light conditions and has a delay feature that keeps lights on for a set period after vehicle shutdown...
The most common cause of B1590 (Autolamp Delay Increase Circuit Short To Ground) is: Damaged or chafed wiring harness causing short to ground in the autolamp delay circuit
Typical repair costs for B1590 range from $100 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving as this affects only the convenience feature of delayed headlight shutoff. The primary headlight operation and safety lighting functions remain unaffected, but the autolamp delay feature will not function properly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1590 to identify the root cause.
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Quick Info
Category
Body
System
Exterior Lighting Control System
Difficulty
Type
Manufacturer
Recommended Tools
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