B1305 — Accessory Delay Relay Coil Circuit Short To Ground

What is the most common cause of B1305?

The most common causes are: faulty ignition control circuit in the ECM, moisture or oil in the spark plug wells, failed ignition coil or coil pack.

What does OBD2 code B1305 mean?

Accessory Delay Relay Coil Circuit Short To Ground (B1305): a body electrical fault affecting the ignition system. Short, gentle driving to a shop is usually possible. Most often caused by faulty ignition control circuit in the ECM, moisture or oil in the spark plug wells, failed ignition coil or coil pack.

Is it safe to drive with B1305?

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.

How do I diagnose B1305 myself?

Start with a scan: confirm B1305, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the ignition system, and verify the suspect component against live data before buying parts.

How much does it cost to fix B1305?

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

When a scan tool displays trouble code B1305, the vehicle's control module is reporting that it has detected a short circuit to ground in the accessory delay relay coil circuit. This falls within the body electrical group of the OBD2 standard, which means the issue affects systems beyond the engine management itself — specifically the relay that controls accessory power in certain ignition states. The fault is electrical in nature and involves the coil winding inside the accessory delay relay, which has shorted against ground somewhere in its control circuit.

To understand why B1305 sets, it helps to know what the accessory delay relay does. This relay keeps certain electrical accessories — such as the radio, power windows, or interior lights — powered for a short period after the ignition is turned off. The relay coil receives a signal from the body control module or instrument cluster. When that coil circuit experiences a short to ground, the module interprets this as a fault condition and logs B1305. The control module does not register this code from a single anomalous reading; instead, it requires the fault condition to occur repeatedly under specific operating parameters before illuminating the Check Engine Light. When B1305 is stored, the associated freeze frame data captures engine load, RPM, coolant temperature, and vehicle speed at the moment the fault was detected. Reproducing those exact conditions during diagnosis is essential for an accurate test.

Common Symptoms of B1305

The symptoms associated with B1305 reflect a compromised ignition or accessory circuit:

• Check Engine Light is illuminated on the dashboard
• Noticeable loss of engine power, often accompanied by jerking during acceleration
• Fuel consumption increases noticeably compared to normal driving
• Engine misfires occur either under load or at idle
• Difficulty starting the engine, particularly in humid or wet conditions

What Causes B1305?

The root causes of B1305 range from environmental contamination to component failure:

• Moisture or oil intrusion in the spark plug wells
• Damaged or corroded wiring and connectors related to the coil circuit
• Failure of the ignition coil or coil pack
• Faulty ignition control circuit within the ECM itself

How to Diagnose B1305

Follow this logical sequence to isolate the cause of B1305:

1. Connect an OBD2 scanner and confirm B1305 is stored in the module's memory. Save the freeze frame data — it documents engine load, RPM, temperature, and speed when the fault first appeared, which guides your testing.
2. Look for related diagnostic trouble codes that may point to the underlying cause. Also search for technical service bulletins specific to your vehicle make and model — many B0xxx codes have known fixes or software updates documented by the manufacturer.
3. Perform a thorough visual inspection of the wiring harness and connectors tied to the ignition system. Look for damaged insulation, corrosion, chafing from contact with other components, or loose-fitting terminals.
4. Test the ignition coil by swapping it with a known-good unit from another cylinder. If B1305 follows the coil to its new position, the coil is confirmed faulty.
5. Remove and inspect the spark plugs. Check for electrode wear, oil fouling, carbon tracking on the ceramic insulator, and verify the gap matches specifications.
6. Clear the code, then drive the vehicle through a complete drive cycle that recreates the freeze frame conditions. If B1305 does not return, the issue was likely intermittent.

Repair Options for B1305

Address the most accessible and common failures before committing to expensive replacements:

• Replace an ignition coil — $150–$380
• Replace spark plugs — $90–$250
• Repair coil wiring or connector — $80–$250

How Much Does It Cost to Fix B1305?

The total expense for repairing B1305 depends entirely on which component is responsible. Parts and labor at independent shop rates typically break down as follows: ignition coil replacement runs $150–$380, spark plug replacement costs $90–$250, and wiring or connector repair ranges from $80–$250. Most vehicles see repairs fall between $80 and $380 total. Proper diagnosis before purchasing parts is the single most effective way to control costs — the most expensive scenario is rarely the first one to investigate.

Can You Drive with B1305?

This code warrants caution. Ignition-related faults cause misfires that allow unburned fuel to enter the exhaust stream, where it can overheat and destroy the catalytic converter. If the Check Engine Light begins flashing, indicating an active and severe misfire, stop driving immediately and address the problem before continuing.

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
• B1304: Accessory Delay Relay Coil Circuit Short To Battery
• B1306: Oil Level Switch Circuit Open