What Does B1574 Mean?
This code indicates the Body Control Module (BCM) has detected a short to ground in the left rear door ajar switch circuit. The BCM monitors this circuit to determine if the left rear door is open or closed. When a short to ground occurs, the circuit voltage drops below the expected threshold, causing the BCM to set this fault code and potentially trigger false door ajar warnings.
Common Causes
45%
Damaged or chafed wiring harness in the door jamb area where wires flex during door opening and closing
30%
Faulty door ajar switch with internal short to ground or corroded terminals
15%
Water intrusion or corrosion in door jamb connector causing short circuit
10%
BCM internal fault or damaged BCM connector terminal
Diagnostic Steps
1
Step 1: Perform visual inspection of left rear door jamb area for damaged, pinched, or chafed wiring, paying attention to the rubber boot where wires pass from body to door. Check for bare wires touching ground.
2
Step 2: Disconnect the left rear door ajar switch connector and measure resistance to ground on the BCM signal wire (door side disconnected). Reading should be infinite (open circuit); if continuity to ground exists, repair short in wiring harness.
3
Step 3: If wiring is intact, test the door ajar switch itself by measuring resistance across switch terminals with door open and closed. Typical values: open when door closed (infinite resistance), closed to ground when door open (near 0 ohms). Replace switch if readings are incorrect or switch shows continuity to ground when door is closed.
4
Step 4: Inspect door jamb connector for water intrusion, corrosion, or pushed-back pins. Clean terminals with electrical contact cleaner and apply dielectric grease. Ensure connector seals are intact.
5
Step 5: If all previous checks pass, verify BCM connector terminals for damage or corrosion at the door ajar circuit pins. Check BCM ground circuits for integrity.
6
Step 6: Clear codes and cycle door open/closed multiple times while monitoring live data to confirm repair. Verify interior lights and door ajar warning function correctly without false alerts.
Estimated Repair Cost
$75 - $350
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a short to ground in the left rear door ajar switch circuit. The BCM monitors this circuit to determine if the left rear door is open or closed. When a short to ground occurs, the circuit voltage drops below the expected threshold, causi...
The most common cause of B1574 (Door Ajar LR Circuit Short To Ground) is: Damaged or chafed wiring harness in the door jamb area where wires flex during door opening and closing
Typical repair costs for B1574 range from $75 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive with this code, though it may cause false door ajar warnings, interior lights staying on draining the battery, and potential inability to arm security system. Repair at earliest convenience to prevent battery drain issues.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1574 to identify the root cause.
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Quick Info
Category
Body
System
Body Control and Convenience Systems
Difficulty
Type
Manufacturer
Recommended Tools
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