What Does B1303 Mean?
This code indicates the Body Control Module (BCM) has detected an open circuit in the accessory delay relay coil circuit. The accessory delay relay controls power to accessories like power windows, radio, and interior lights for a programmed time after the ignition is turned off. An open circuit means the BCM cannot energize the relay coil, preventing the accessory delay function from operating properly.
Common Causes
40%
Failed accessory delay relay with open internal coil winding
35%
Broken or disconnected wiring between BCM and relay coil, including damaged connector terminals
15%
Corroded or loose relay socket connections in power distribution center
10%
Failed BCM relay driver circuit or internal BCM fault
Diagnostic Steps
1
Step 1: Locate the accessory delay relay in the power distribution center (fuse box) and inspect for physical damage, corrosion, or loose connections. Remove relay and inspect socket terminals for burning, corrosion, or bent pins.
2
Step 2: Using a digital multimeter, measure resistance across the relay coil terminals (typically pins 85 and 86). Reading should be between 70-120 ohms for most relays. Infinite resistance indicates open coil.
3
Step 3: With relay removed, test the circuit by measuring resistance from the BCM connector relay control pin to the relay socket ground pin. Should read less than 5 ohms. Check power supply pin at relay socket for battery voltage with ignition on.
4
Step 4: If relay and socket are good, inspect wiring harness from BCM to relay socket for cuts, pinches, or chafing damage. Pay special attention to areas where harness passes through grommets or near moving components.
5
Step 5: Substitute a known-good relay of same type and clear codes. Cycle ignition and test accessory delay function. If code returns immediately, suspect BCM driver circuit failure.
6
Step 6: Perform final verification by monitoring relay operation with scan tool while activating accessory delay function. Confirm all accessories operate correctly during delay period after ignition off.
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected an open circuit in the accessory delay relay coil circuit. The accessory delay relay controls power to accessories like power windows, radio, and interior lights for a programmed time after the ignition is turned off. An open circuit mea...
The most common cause of B1303 (Accessory Delay Relay Coil Circuit Open) is: Failed accessory delay relay with open internal coil winding
Typical repair costs for B1303 range from $75 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 convenience features like accessory power retention after key-off. Accessories may shut off immediately when ignition is turned off rather than staying on for the programmed delay period.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1303 to identify the root cause.
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Quick Info
Category
Body
System
Body Control System
Difficulty
Type
Manufacturer
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