B1305

Accessory Delay Relay Coil Circuit Short To Ground

Body Chassis/Safety Accessory Control Circuit 🟢 Low — Fix at next service ✅ Safe to Drive
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What This Actually Means

In plain language — no jargon

The accessory delay relay's electrical coil is shorted to ground, causing it to fail activation. Think of it like a light switch that's stuck because its wiring is touching the metal frame.

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Symptoms You May Notice

3 known symptoms for this code
Accessories (power windows, locks, wipers) may not function or operate intermittently
Battery drain or parasitic draw when vehicle is off
Check Engine or Body Control Module warning light illuminated
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the coil circuit resistance and voltage when commanding the accessory delay relay on and off. It detects abnormally low resistance (short to ground) by measuring excessive current draw or zero voltage drop across the coil. A healthy coil shows resistance in the 50-100 ohm range; a short shows near-zero resistance.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Coil Resistance 50-100 ohms Below 10 ohms or short detected
Coil Voltage (energized) 11-14V 0V or excessive current draw
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Accessory Delay Relay
Locate and replace the relay with an OEM equivalent; most relays are simple plug-and-play modules.
2
Relay Socket and Wiring Harness
Inspect the relay socket and wiring for corrosion, moisture, or damaged insulation; clean or reseat connectors.
3
Body Control Module (BCM) Wiring Harness
Check for pinched, chafed, or wet wiring between the BCM and relay; repair insulation or routing as needed.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code B1305 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code B1305

What happens after you fix the fault

Once the fault is repaired, B1305 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.