What Does P1266 Mean?
The ECM has detected a high-to-low side short circuit condition in the cylinder #1 fuel injector driver circuit. This is an alternate manufacturer-specific code for the same condition as P1261, typically used by different vehicle manufacturers or ECM calibrations. The injector's power supply and ground control wires have an unintended connection, preventing proper fuel injection control.
Safety Warning
A shorted injector driver circuit causes a persistent misfire with rough running and loss of power. This can be dangerous during acceleration or highway driving. Extended misfiring damages the catalytic converter and risks ECM driver damage.
Common Causes
35%
Chafed or damaged injector wiring with high-side and low-side conductors contacting each other
30%
Failed cylinder #1 fuel injector with internal coil short circuit
20%
Corroded or water-infiltrated injector connector at cylinder #1
15%
ECM injector driver circuit internal failure
Diagnostic Steps
1
Check for cylinder #1 misfire code (P0301) and any other injector circuit codes to determine the scope of the problem.
2
Disconnect the cylinder #1 fuel injector and inspect the connector for corrosion, heat damage, or contamination between the pin cavities.
3
Measure the fuel injector coil resistance and compare to specification. Verify no continuity exists between the injector terminals and the injector body.
4
With the injector disconnected, check for continuity between the two harness-side wires — any continuity indicates a wiring short that must be repaired.
5
Perform an injector swap test by moving the cylinder #1 injector to another cylinder location, clearing codes, and running the engine to determine if the fault follows the injector or stays with the wiring.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
The ECM has detected a high-to-low side short circuit condition in the cylinder #1 fuel injector driver circuit. This is an alternate manufacturer-specific code for the same condition as P1261, typically used by different vehicle manufacturers or ECM calibrations. The injector's power supply and gro...
The most common cause of P1266 (Cylinder #1 High To Low Side Short) is: Chafed or damaged injector wiring with high-side and low-side conductors contacting each other
Typical repair costs for P1266 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A shorted injector driver circuit causes a persistent misfire with rough running and loss of power. This can be dangerous during acceleration or highway driving. Extended misfiring damages the catalytic converter and risks ECM driver damage.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1266 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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