What Does P1264 Mean?
The ECM has detected a high-to-low side short circuit in the cylinder #4 fuel injector driver circuit. The power supply and ground control wires for cylinder #4's injector have an unintended electrical connection, compromising the ECM's ability to control fuel delivery to this cylinder. This results in a cylinder #4 misfire with rough engine operation and loss of power.
Safety Warning
A shorted injector circuit causes persistent misfire, rough running, and loss of power which can be hazardous when merging or passing. Unburned fuel from the dead cylinder damages the catalytic converter over time. There is also risk of damaging the ECM's injector driver circuit.
Common Causes
35%
Damaged or melted wiring in the cylinder #4 injector harness causing a high-to-low side short
30%
Failed fuel injector on cylinder #4 with shorted coil windings
20%
Corroded or water-damaged connector at the cylinder #4 injector
15%
ECM internal driver circuit failure for cylinder #4 injector
Diagnostic Steps
1
Check for cylinder #4 misfire code (P0304) and other injector driver codes to map the scope of the problem.
2
Disconnect the cylinder #4 injector connector and inspect for heat damage, corrosion, or any debris bridging the connector pins.
3
Measure the fuel injector coil resistance and verify it matches manufacturer specifications. Check for any short to the injector body.
4
With the injector disconnected, verify the harness wires show no continuity between them at the connector — this rules out a wiring short.
5
Swap the cylinder #4 injector with another cylinder's injector, clear codes, and operate the engine to determine if the fault follows the injector or stays with the cylinder #4 circuit.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
The ECM has detected a high-to-low side short circuit in the cylinder #4 fuel injector driver circuit. The power supply and ground control wires for cylinder #4's injector have an unintended electrical connection, compromising the ECM's ability to control fuel delivery to this cylinder. This results...
The most common cause of P1264 (Cylinder #4 High To Low Side Short) is: Damaged or melted wiring in the cylinder #4 injector harness causing a high-to-low side short
Typical repair costs for P1264 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A shorted injector circuit causes persistent misfire, rough running, and loss of power which can be hazardous when merging or passing. Unburned fuel from the dead cylinder damages the catalytic converter over time. There is also risk of damaging the ECM's injector driver circuit.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1264 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel Injection System
Difficulty
Type
Manufacturer
Recommended Tools
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