B1304 — Accessory Delay Relay Coil Circuit Short To Battery

How much does it cost to fix B1304?

Replace an ignition coil — $150–$380; Repair coil wiring or connector — $80–$250; Replace spark plugs — $90–$250. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What are the symptoms of B1304?

Drivers most often notice: hard starting, especially in damp weather, Check Engine Light on, increased fuel consumption, loss of power and jerking.

Will B1304 clear itself?

Sometimes B1304 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

Is it safe to drive with B1304?

Drive with caution and avoid load. Ignition faults cause misfires that quickly overheat and destroy the catalytic converter; if the Check Engine Light flashes, stop and fix it first.

What is the most common cause of B1304?

The most common causes are: damaged coil wiring or connector, failed ignition coil or coil pack, worn spark plugs or wrong plug gap.

When your scan tool pulls code B1304, it's telling you the powertrain or body control module has detected a specific electrical fault: the accessory delay relay coil circuit is showing a direct short to battery voltage. This isn't a generic engine problem—B1304 belongs to the body electrical family within the OBD2 standard, which means the issue lives in the vehicle's accessory power management system rather than in core engine mechanics. The module monitors this circuit constantly, and when it sees battery voltage bleeding where it shouldn't be, it flags the condition and illuminates the Check Engine Light.

The module doesn't set B1304 on a single momentary glitch. It requires the fault condition to repeat under specific operating parameters before logging the code and turning on the warning lamp. This is important because the freeze frame data stored alongside B1304 captures the exact engine conditions—load, RPM, temperature, vehicle speed—when the problem first appeared. Those readings are your roadmap for reproduction during diagnosis. If the freeze frame shows the fault occurred at idle with the engine at operating temperature, that's exactly where you need to be when you retest.

The accessory delay relay coil manages power to secondary electrical systems, allowing them to remain active for a preset period after the ignition is turned off. When a short to battery develops in this circuit, the coil receives excessive voltage, which can cause erratic accessory operation, draining, or complete failure of the affected systems. In some vehicle designs, this fault can also interfere with normal ignition switching, leading to the hard starting and misfire symptoms commonly reported with B1304.

Symptoms

• Engine cranks slowly or fails to start, particularly in humid or wet conditions
• Check Engine Light remains illuminated after the fault is detected
• Noticeable increase in fuel consumption compared to normal driving patterns
• Reduced engine performance with hesitation or jerking during acceleration
• Cylinder misfires occurring either at idle or under load
• Intermittent electrical accessory behavior or complete accessory failure

Causes

• Damaged or corroded wiring harness and connectors in the ignition or accessory circuit
• Failed ignition coil or coil pack delivering incorrect output
• Worn, improperly gapped, or damaged spark plugs
• Moisture intrusion or oil contamination in the spark plug tube wells
• Poor electrical connections at the accessory delay relay or related modules

How to Diagnose B1304

1. Connect your OBD2 scanner and verify that B1304 is an active or stored code. Save the associated freeze frame data before clearing anything—this snapshot tells you precisely what engine conditions existed when the module first detected the fault.

2. Check for any related diagnostic trouble codes. Secondary codes often point toward the root cause, such as misfire counts or other electrical system failures. Also search manufacturer technical service bulletins using your vehicle's VIN—many B0xxx code patterns have documented factory fixes or software calibrations.

3. Perform a thorough visual inspection of all wiring and connectors tied to the ignition and accessory delay systems. Look for chafed insulation, bent pins, corrosion buildup, or connectors that aren't fully seated. Pay special attention to areas near heat sources or moving components.

4. Test the ignition coil output with a multimeter or oscilloscope. If coil resistance falls outside manufacturer specifications, or if swap testing to another cylinder relocates the fault code to that cylinder, the coil is confirmed faulty.

5. Remove and inspect spark plugs for signs of wear, carbon fouling, oil saturation, or incorrect electrode gap. Replace as needed and verify the spark plug wells are dry and clean.

6. Clear B1304 after repairs, then complete a full drive cycle that reproduces the conditions recorded in the freeze frame. The code must stay cleared for the fault to be considered resolved.

Repair Options

Depending on which component is actually responsible for B1304, here are typical repair scenarios with parts and labor at independent shop rates:

• Ignition coil replacement: $150–$380
• Coil wiring or connector repair: $80–$250
• Spark plug replacement: $90–$250

How Much Does It Cost to Fix B1304?

The total repair cost for B1304 typically falls between $80 and $380 depending on which component requires attention. Ignition coil issues tend toward the higher end of the range, while wiring repairs or spark plug service occupy the lower to mid range. The most important step is accurate diagnosis before purchasing parts—assuming the worst and replacing multiple expensive components first rarely makes financial sense. Start with inspection and testing, then address only what the evidence supports.

Can You Drive with B1304?

Proceed with caution. While a short-to-battery condition in the accessory delay circuit may seem minor, the resulting ignition irregularities can cause persistent misfires that overheat and destroy the catalytic converter—a costly repair that could be avoided by addressing B1304 promptly. If the Check Engine Light is flashing rather than steady, stop driving immediately and have the vehicle towed. Flashing indicates an active misfire severe enough to risk catalytic converter damage within minutes.

Related OBD2 codes

• B1300: Power Door Lock Circuit Failure
• B1301: Power Door Lock Circuit Open
• B1302: Accessory Delay Relay Coil Circuit Failure
• B1303: Accessory Delay Relay Coil Circuit Open
• B1305: Accessory Delay Relay Coil Circuit Short To Ground
• B1306: Oil Level Switch Circuit Open