What Does B1304 Mean?
This code indicates the Body Control Module (BCM) has detected that the accessory delay relay coil circuit is shorted directly to battery voltage when it should not be. The accessory delay relay controls power to various accessories after the ignition is turned off, allowing functions like power windows, radio, and interior lights to operate for a limited time. The BCM detected an unexpected voltage present on the relay control circuit, indicating a short to positive battery voltage in the wiring or relay coil itself.
Common Causes
45%
Damaged or chafed wiring harness causing short to battery voltage in the relay coil control circuit
30%
Failed accessory delay relay with internal short circuit
15%
Moisture or corrosion in relay socket or connector causing cross-circuit short
10%
Failed Body Control Module with internal driver circuit fault
Diagnostic Steps
1
Step 1: Locate the accessory delay relay (typically in the power distribution center or fuse box) and remove it. Use a multimeter to measure resistance across the relay coil terminals - should read 60-120 ohms typically. If shorted (near 0 ohms) or open (infinite resistance), replace relay.
2
Step 2: With relay removed and ignition off, measure voltage at the BCM-controlled relay coil terminal in the relay socket. Should read 0V. If battery voltage is present, there is a short to power in the wiring between BCM and relay socket.
3
Step 3: Inspect the wiring harness from the BCM to the relay socket for any visible damage, chafing against metal surfaces, pinch points at body seams, or evidence of previous repair. Pay special attention to areas where harness passes through firewalls or near hood hinges.
4
Step 4: Disconnect the BCM connector and check for moisture, corrosion, or pushed-back pins at the accessory relay control circuit terminal. Measure resistance from the BCM connector terminal to the relay socket terminal - should read less than 5 ohms. Also verify no continuity to battery voltage with all connections separated.
5
Step 5: If all wiring and relay test good, reconnect all components, clear codes, and monitor. If code returns immediately without activating the relay, the BCM internal driver circuit is likely failed and BCM replacement is necessary.
Estimated Repair Cost
$100 - $800
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected that the accessory delay relay coil circuit is shorted directly to battery voltage when it should not be. The accessory delay relay controls power to various accessories after the ignition is turned off, allowing functions like power win...
The most common cause of B1304 (Accessory Delay Relay Coil Circuit Short To Battery) is: Damaged or chafed wiring harness causing short to battery voltage in the relay coil control circuit
Typical repair costs for B1304 range from $100 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is generally safe to drive, but accessory functions may not work properly after key-off, potentially draining the battery or leaving accessories inoperative. Repair within a week to prevent battery discharge and restore proper accessory function.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1304 to identify the root cause.
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Quick Info
Category
Body
System
Body Electrical System
Difficulty
Type
Manufacturer
Recommended Tools
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