B1303 — Accessory Delay Relay Coil Circuit Open #

Note: The description for this DTC may vary depending on the vehicle manufacturer. Always refer to your specific service manual for exact wording. Below are known label variations:

• Accessory Delay Relay Circuit Open (Ford)
• Accessory Power Relay Coil Circuit Open (GM/Chevrolet)
• Accessory Delay Relay Control Circuit Open (Lincoln)

Summary of DTC B1303 #

The B1303 code indicates that the vehicle’s accessory delay relay—a component responsible for maintaining power to certain electrical accessories (like windows or radio) after the ignition is turned off—has an open circuit in its coil control circuit. In simple terms, the relay that keeps your accessories running for a short period after turning off the key is not being energized as expected, typically due to a break or high resistance in its control wiring. When this code sets, the vehicle’s onboard diagnostics (OBD-II/EOBD, which stands for On-Board Diagnostics Second Generation/European On-Board Diagnostics) system has detected the fault and stored it in memory. While B-codes generally relate to body and comfort systems rather than core engine functions, their impact can still be felt in daily convenience features. This code often requires electrical troubleshooting and sometimes component replacement to restore normal accessory function.

Frequent Symptoms for DTC B1303 #

A B1303 code doesn’t usually leave you stranded, but it can be a source of frustration due to lost convenience features. The most common symptoms are related to the accessory systems not behaving as expected when the ignition is turned off.

• Power windows stop working immediately after key-off (no “delay” period).
• Radio or infotainment system cuts off the moment the ignition is switched off.
• Sunroof or other powered accessories lose delay function after key removal.
• No audible relay click when accessories should be powered after key-off.
• Sometimes, a related warning message may appear on the instrument cluster.

Probable Causes (Ranked by Frequency) for DTC B1303 #

The causes of a B1303 code tend to follow a pattern, with wiring and relay issues being the most common culprits. Here’s what to check, in order of likelihood:

1. Failed accessory delay relay (the relay itself is internally open or has a broken coil).
2. Open circuit or high resistance in relay control wiring (corroded, cut, or disconnected wires).
3. Faulty relay control module (if the vehicle uses a separate electronic module to command the relay).
4. Poor or loose connection at relay socket or associated connectors.
5. Blown fuse or power supply issue to relay coil circuit.

Step-by-Step Diagnostic for DTC B1303 #

Diagnosing a B1303 code requires a methodical approach, starting with the simplest checks and moving to more technical ones. Always ensure the battery is disconnected before working on electrical systems for safety.

• Step 1: Verify the code with a scan tool and clear it. If it returns, proceed.
• Step 2: Locate the accessory delay relay (consult the OEM wiring diagram or owner’s manual for location).
• Step 3: Inspect the relay and its socket for corrosion, damage, or loose fit.
• Step 4: Test the relay coil for continuity using a multimeter. An infinite reading means the coil is open (replace relay).
• Step 5: Check for continuity and voltage on the relay coil control circuit (wiring from ignition switch or control module to relay).
• Step 6: Inspect related fuses and power feeds for proper operation.
• Step 7: If all hardware checks out, use a wiring diagram to trace the circuit for any breaks, shorts, or connection issues up to the control module.
• Step 8: As a last resort, test or swap the accessory delay relay control module, if equipped.

Possible Repairs for DTC B1303 #

The necessary repair will always depend on what you find during diagnosis. Here are the most common solutions, matched to their likely causes:

• Replace the accessory delay relay if the coil is open or the relay fails bench testing.
• Repair or replace damaged wiring in the relay coil circuit (fix broken wires, clean corrosion, or secure loose connections).
• Replace or reprogram the relay control module if it’s determined to be faulty (consult OEM procedures).
• Replace blown fuses and address underlying power supply issues (check for short circuits causing fuse to blow).
• Clean and secure relay socket connections if contact quality is poor.

Can You Drive with B1303? #

Yes, but with limitations. The B1303 code does not affect core engine or drivetrain systems and will not leave you stranded. However, you’ll lose the accessory delay function—so power windows, radio, or sunroof may stop working the moment you turn off the ignition. This can be inconvenient but is not a safety issue. If you rely on these features (for example, to close windows after shutting off the car), you’ll want to repair the fault soon to restore normal operation.

Vehicles Most Commonly Affected by B1303 #

B1303 is most frequently reported on vehicles from brands that use an accessory delay relay for comfort features, especially American OEMs. The following vehicles and model years see this code most often:

• Ford F-Series trucks (F-150, F-250) — various model years
• Ford Explorer and Expedition
• Chevrolet Silverado and Tahoe
• Lincoln Navigator
• GMC Sierra

Always check your vehicle’s OEM service information for specific diagnostic and repair procedures!

Common Mistakes & Best Practices for B1303 #

Even experienced technicians can overlook key steps when chasing intermittent electrical faults. Here are the most common errors—and how to avoid them:

• Replacing the relay without testing the wiring first—always use a multimeter to confirm the real source of the open circuit.
• Ignoring corroded or loose connections at the relay socket—these are a frequent cause of open circuits.
• Overlooking related fuses or power supply feeds—don’t just focus on the relay.
• Failing to consult the OEM wiring diagram—manufacturer variations can mislead even seasoned pros.
• Clearing the code without fixing the underlying problem—it will return, and the inconvenience will persist.

FAQ Express: B1303 #

Got questions? Here are quick answers to the most common concerns about this code:

• Q: Will B1303 cause my car to stall or not start?
  A: No, B1303 affects only accessory circuits (like windows and radio), not engine or starting systems.
• Q: Can I bypass the accessory delay relay?
  A: It’s not recommended. Bypassing can disable convenience features and may cause electrical issues. Always repair the fault or replace the relay as designed.
• Q: Why did this code appear after a battery replacement?
  A: Sometimes, disturbed connections or electrical surges can reveal a marginal relay or wiring fault. Double-check all related connectors during diagnosis.