B1304 — Accessory Delay Relay Coil Circuit Short To Battery #

Note: The wording for DTC B1304 may vary depending on the automaker. Always check your OEM (Original Equipment Manufacturer) documentation for the most accurate description.

• Accessory Delay Relay Coil Circuit Short To Battery (Generic, Ford, GM, Chrysler, Honda, Toyota)
• Accessory Delay Relay Circuit High (Ford)
• Accessory Delay Relay Input Circuit Shorted High (GM)

Summary of the B1304 Code #

The B1304 code is a Body Control Module (BCM) diagnostic trouble code (DTC) that indicates the accessory delay relay coil circuit is shorted to battery voltage. This relay controls the timed power supply to certain accessories—like power windows or the radio—after the ignition is turned off. When the circuit is “shorted to battery,” it means the relay coil is receiving continuous voltage, which can cause accessories to stay powered on longer than intended. This fault is typically detected by the BCM, which monitors current flow and voltage levels in the accessory delay relay circuit. If the system finds an unexpected voltage where there shouldn’t be, it sets the B1304 code and may trigger a warning or unusual accessory behavior.

Frequent Symptoms for the B1304 Code #

Drivers and technicians may notice several telltale signs if the B1304 code is present. Most often, these involve electrical accessories behaving abnormally after the ignition has been switched off. Since the relay is designed to delay power cutoff, a short can confuse the system and keep certain features powered up, sometimes draining the battery.

• Accessories (like radio or windows) remain powered after key-off
• Battery drain when the vehicle sits for long periods
• No timed power to accessories (i.e., they shut off immediately)
• Intermittent electrical glitches in the accessory circuit
• Possible warning lights or messages on the dashboard

Probable Causes for B1304 (Ranked by Likelihood) #

The root of a B1304 code almost always involves a fault in the accessory delay relay or its related wiring. However, the specific culprit can range from simple corrosion to a rare BCM fault. Here’s what to look for, in order of probability:

1. Shorted accessory delay relay (internal relay failure)
2. Wiring harness damage (chafed, pinched, or corroded wires in the relay circuit)
3. Faulty relay socket or connector (loose, corroded, or damaged pins)
4. Incorrect replacement relay (wrong part installed)
5. BCM failure (rare, but possible if all else checks out)

Step-by-Step Diagnostic for B1304 #

Diagnosing the B1304 code doesn’t require advanced tools, but following a logical process will save time and frustration. Here’s how a professional would approach it:

• Verify the code and check for related DTCs using a scan tool.
• Consult the wiring diagram for the accessory delay relay circuit (OEM manual).
• Inspect the relay and its socket for visible damage, corrosion, or overheating.
• Test the relay coil resistance with a multimeter; compare to OEM specifications.
• Check for battery voltage at the relay coil circuit with the ignition off and on.
• Inspect wiring harness for pinched, chafed, or shorted wires between the relay and BCM.
• Replace the relay with a known good unit and retest.
• If the problem persists, check BCM outputs and continuity to the relay circuit.

Possible Repairs for B1304 #

Fixing the B1304 code depends on the exact cause identified during diagnosis. Most repairs are straightforward, focusing on the relay and wiring. Here are the typical solutions:

• Replace the accessory delay relay if it tests faulty or is shorted internally.
• Repair or replace damaged wiring or connectors in the relay circuit.
• Clean and secure all electrical connections to the relay and BCM.
• Install the correct OEM relay if an incorrect part was previously used.
• Replace the Body Control Module (BCM) only if all other causes are eliminated and verified.

Is It Safe to Drive With B1304? #

Limited. You can usually drive with the B1304 code present, since it rarely affects engine performance or critical safety systems. However, if the relay circuit keeps accessories powered after shutdown, you risk a dead battery if the vehicle sits unused. If you notice ongoing power to accessories or repeated battery drain, the vehicle should be serviced promptly to avoid getting stranded.

Vehicles Most Commonly Affected by B1304 #

This code is most often seen on North American vehicles, especially from manufacturers who use accessory delay features. It’s not unique to any one brand, but certain models show it more frequently:

• Ford F-150, Escape, Explorer, Taurus
• Chevrolet Silverado, Malibu, Impala
• Dodge Ram, Chrysler Town & Country, Jeep Grand Cherokee
• Honda Accord (with accessory delay relay)
• Toyota Camry, Sienna (select models)

Common Mistakes & Best Practices for B1304 #

It’s easy to jump to conclusions with electrical faults, but a methodical approach avoids wasted time and parts. Here’s what to watch out for:

• Replacing the relay without inspecting wiring or the relay socket
• Overlooking obvious signs of corrosion or water intrusion
• Using a non-OEM relay that doesn’t match the circuit’s requirements
• Ignoring intermittent symptoms that could point to a loose pin or connector
• Not clearing the code after a repair to verify the fix

Quick FAQ for B1304 #

Here are answers to some common questions drivers and technicians ask about this code:

• Q: Can I just remove the accessory delay relay to fix the problem?
  A: Removing the relay will disable the accessory delay feature, but it won’t fix the underlying short. The code will likely remain, and some comfort features may stop working as intended.
• Q: Could a dead battery be caused by B1304?
  A: Yes, if the short keeps accessories powered up after the ignition is off, it can slowly drain the battery over time.