Faulty cylinder 1 fuel injector with an internal short in its coil or solenoid; Damaged, chafed or shorted wiring between the PCM or injector driver module and the cylinder 1 injector; Corroded, loose or water-contaminated injector connector or harness plug; Injector wiring shorted to the neighbouring circuit or to the cylinder head through damaged insulation; Fault in the PCM or separate injector driver module; Outdated PCM calibration where a manufacturer service bulletin applies to the vehicle.

P1261

Cylinder #1 High To Low Side Short.

Ford
Powertrain
Manufacturer code
Medium severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
2: AreaFuel and air metering (injector circuit)
61: FaultThe specific fault in that area

What it means

On Ford, P1261 means the powertrain control module has detected a short between the high side and low side of the cylinder 1 fuel injector circuit. This is an electrical fault in the injector driver circuit, not a mechanical engine fault. It is typically found on Ford diesel and some direct injection applications, but the exact injector system varies by model and engine, so check the manufacturer data for your vehicle.

Symptoms

Engine warning light on
Misfire or rough running, mainly on cylinder 1
Engine running on fewer cylinders or reduced power
Hard starting or no start
Poor fuel economy
Engine may enter a limp-home mode

Possible causes

Faulty cylinder 1 fuel injector with an internal short in its coil or solenoidlikely
Damaged, chafed or shorted wiring between the PCM or injector driver module and the cylinder 1 injectorlikely
Corroded, loose or water-contaminated injector connector or harness plugpossible
Injector wiring shorted to the neighbouring circuit or to the cylinder head through damaged insulationpossible
Fault in the PCM or separate injector driver modulerare
Outdated PCM calibration where a manufacturer service bulletin applies to the vehiclerare

How to diagnose

Read all stored and pending codes and note the freeze frame data, then check for other injector or misfire codes.
Check for relevant manufacturer service bulletins for the model and engine.
Visually inspect the cylinder 1 injector connector and harness for chafing, heat damage, corrosion, water ingress and poor terminal tension.
Check the harness route near the cylinder head and engine mounts for rubbing or pinching.
With the connector unplugged and ignition off, measure the injector coil resistance and compare it with the specification for the engine.
Check the injector circuit wiring for continuity, and for shorts to ground, to voltage and to other circuits, following the wiring diagram.
Swap the injector with another cylinder if the design allows, clear the code and see whether the fault follows the injector.
If wiring and injector test good, test the PCM or driver module output as per manufacturer procedure.

How to fix

Replace the cylinder 1 injector if its resistance or operation is out of specification, following the procedure for the engine, including any coding or adaptation needed.
Repair or replace damaged wiring and fix any short between circuits.
Clean, repair or replace the corroded or damaged injector connector and terminals.
Secure and reroute the harness to prevent further chafing.
Replace or reprogram the PCM or driver module only after confirming it is faulty, or update the calibration if a service bulletin identifies it as a known cause.

Can I keep driving?

Medium severity

The car may be driven a short distance if it runs acceptably, but get it checked soon. A shorted injector circuit can cause misfire, reduced power and possible damage, so avoid driving if it runs very roughly or goes into limp mode.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.