C1264
Lamp Warning Relay Circuit Short To Battery
Chassis Chassis/Safety Warning Lamp Relay 🔴 Serious — Stop or limit driving
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What This Actually Means
In plain language — no jargon

The warning lamp relay circuit is shorted directly to battery voltage, meaning it's receiving constant power instead of being controlled by the ECU. Think of it like a light switch that's stuck in the ON position because a wire is touching the positive battery terminal.

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Symptoms You May Notice
3 known symptoms for this code
Warning lamp stays on continuously or flickers erratically
Loss of warning lamp control from the ECU
Possible electrical burning smell near relay or wiring harness
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors the lamp relay circuit voltage and expects it to toggle between ground and battery voltage under its control. When the ECU commands the lamp OFF, it should see near-ground voltage; when ON, it should see battery voltage. A short to battery means the circuit remains at battery voltage regardless of ECU commands, triggering the fault.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Relay Circuit Voltage 0V (OFF) to 12-14V (ON) under ECU control Constant 12-14V regardless of ECU command
Circuit Resistance Open circuit (OFF) or low resistance (ON) Shorted directly to positive battery rail
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Wiring harness inspection
Visually inspect the lamp relay wiring for damaged insulation or pinched wires making unwanted contact with the positive battery line.
2
Lamp relay
Test and replace the lamp relay if it's stuck in the ON position or has internal short to power.
3
ECU connector and pins
Inspect the ECU connector pins for corrosion, loose connections, or bent pins that may prevent proper relay control signaling.