C1264

What Does Code C1264 Mean?

DTC C1264 signifies a detected electrical fault within the “Lamp Warning Relay Circuit,” specifically indicating a short to battery. This diagnostic trouble code is typically generated by a chassis control module, such as the Electronic Brake Control Module (EBCM), Powertrain Control Module (PCM), or Body Control Module (BCM), depending on the vehicle manufacturer and specific warning lamp integration. The module monitors the voltage on the control or load side of a relay responsible for illuminating one or more critical warning lamps (e.g., ABS warning, Brake system warning, Traction Control warning, etc.). A “short to battery” condition means the module has detected an unexpectedly high voltage, often approximating B+ (battery voltage), on this circuit when the relay is commanded off, or when the expected voltage should be significantly lower or grounded. The control module registers this discrepancy, interprets it as an unintended power supply to the circuit, and stores the C1264 code, indicating an electrical integrity issue that could lead to unintended lamp illumination or, in some cases, prevent proper lamp operation.

Common Symptoms

• One or more dashboard warning lights (e.g., ABS, Brake, Traction Control, Stability Control) remain continuously illuminated, even when system conditions would normally dictate they should be off.
• Warning lights that are commanded off by the module may flicker intermittently.
• In some rare cases, symptoms might include a slight parasitic battery drain if the short is consistent and energizing components without the vehicle being in operation.
• Other related DTCs may be present if the warning lamp system is integrated with other safety-critical systems.
• Absence of other noticeable operational issues beyond the illuminated warning lamp(s).

What Causes the Code C1264?

• Damaged or Chafed Wiring: The most prevalent cause involves the wiring harness for the warning lamp relay control circuit or its power supply, which may have become abraded or compromised, leading to direct contact with a constant 12V power source. This can occur due to vibration, improper routing, or contact with sharp metal edges within the vehicle’s chassis or engine bay.
• Defective Warning Lamp Relay: An internal short or failure within the relay itself can cause its contacts to remain closed or its coil to draw excessive current, effectively shorting the controlled circuit to battery voltage even when not commanded by the control module.
• Faulty Control Module: While less common, an internal electrical fault within the EBCM, PCM, BCM, or the specific module responsible for commanding the warning lamp relay can lead to an erroneous B+ output on the relay control circuit, triggering the DTC.
• Corrosion or Water Intrusion: Environmental factors such as moisture ingress into electrical connectors, fuse boxes, or junction blocks can create conductive paths, resulting in an unintended short to battery voltage on the affected circuit.

How to Diagnose and Troubleshoot

Diagnosis of C1264 requires careful electrical testing and adherence to manufacturer-specific wiring diagrams.

1. Preliminary Inspection and DTC Verification:
   • Connect an OBD-II scanner to the vehicle’s DLC. Confirm the presence of C1264 and record any associated freeze frame data. Note if C1264 is a current or historical DTC.
   • Perform a thorough visual inspection of the wiring harness associated with the warning lamp relay. Pay close attention to areas where wiring passes through firewalls, over sharp edges, or through high-vibration zones. Look for signs of chafing, corrosion, melting, or rodent damage.
   • Locate the specific warning lamp relay in question using the vehicle’s service manual or wiring diagram. This relay’s function can vary significantly between models.
2. Relay Testing and Circuit Isolation:
   • With the ignition OFF, carefully remove the identified warning lamp relay from its socket.
   • Using a Digital Multimeter (DMM) set to DC voltage, probe the relay socket terminals. Identify the terminals corresponding to the relay’s coil control signal and its power input.
   • With the ignition ON and the warning lamp system commanded OFF (if applicable), check the voltage at the relay control terminal (the one from the control module). A “short to battery” suggests you will likely measure near battery voltage (e.g., 12V) when it should be 0V or close to ground.
   • If battery voltage is present when it should not be, disconnect the control module suspected of driving this circuit. Re-check the voltage at the relay control terminal. If the voltage drops to 0V after disconnecting the module, the fault is likely internal to the module. If voltage remains, the short exists in the wiring between the relay socket and the module.
   • Test the relay itself: Apply 12V and ground to the coil terminals (refer to relay pinout). Confirm an audible click and use the DMM to check for continuity across the switch contacts. An internal short can sometimes be identified by abnormally high resistance across the coil or unintended continuity across contacts.
3. Wiring Integrity Test:
   • If the short is suspected in the wiring, with the relay removed and the control module disconnected, set the DMM to resistance (Ohms).
   • Measure the resistance between the problematic circuit wire (e.g., the relay control wire from the module or the output wire to the lamps) and a known good chassis ground. There should be infinite resistance (open circuit). Any measurable resistance indicates a short to ground.
   • Measure the resistance between the problematic circuit wire and the B+ power distribution circuit. There should be infinite resistance. Any measurable resistance indicates a short to battery, confirming the C1264 fault.
   • If the wiring is suspect, carefully trace the specific wire back through the harness, disconnecting connectors as necessary, to pinpoint the exact location of the short. Pin-out diagrams will be crucial here.

Recommended Repairs and Solutions

Once the root cause of C1264 has been precisely identified through methodical diagnosis, the following repairs are typically recommended:

• Repair or Replace Damaged Wiring: If the visual inspection or continuity tests reveal chafed, corroded, or shorted wiring, the damaged section must be repaired or replaced. For repairs, use automotive-grade wiring, proper crimp connectors (preferably heat-shrink type), and ensure the repair is sealed from environmental exposure. Re-route and secure the wiring properly to prevent future damage. Never simply use electrical tape over exposed wires; this is a temporary and unreliable fix.
• Replace Defective Warning Lamp Relay: If diagnostic testing confirms the relay itself is internally shorted or faulty, replace it with a new OEM (Original Equipment Manufacturer) or equivalent quality aftermarket relay. Always ensure the replacement relay has identical specifications (voltage, current rating, pin configuration) to the original.
• Replace Faulty Control Module: If all wiring and relay tests confirm their integrity, and the module’s output is consistently supplying battery voltage when not commanded, the control module (e.g., EBCM, BCM) is likely at fault. Module replacement often requires specialized programming or calibration using manufacturer-specific diagnostic tools after installation. Consult the vehicle’s service manual for specific replacement and programming procedures.
• Clean Corroded Connections: If corrosion is found in connectors or fuse boxes, carefully disconnect the components, clean the terminals using an approved electrical contact cleaner and a small brush, then apply dielectric grease to prevent future corrosion before reassembly.
• Clear DTCs and Verify Repair: After any repair, clear the C1264 DTC and any related codes using an OBD-II scanner. Perform a test drive under various operating conditions to confirm the fault does not return and that all warning lamps illuminate and extinguish as expected. Monitor the relevant sensor data or lamp status PIDs (Parameter Identifiers) if available on the scanner.