Injector wiring shorted to earth, chafed or damaged between the injector and the control unit; Faulty cylinder 1 injector with an internal short or low coil resistance; Corroded, loose or damaged injector connector or terminals; Water ingress or contamination in the connector or loom; Faulty injector driver within the engine control unit; Wiring fault caused by a previous repair or aftermarket modification.

P0261

Cylinder 1 Injector A Circuit Low.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
2: AreaFuel and air metering (injector circuit)
61: FaultThe specific fault in that area

What it means

P0261 means the engine control unit has detected a low voltage or low signal in the control circuit for the cylinder 1 fuel injector. The control unit monitors the injector driver circuit and sets the code when the voltage or current is lower than expected, which usually points to a short to earth, a wiring fault or a failed injector or driver.

Symptoms

Malfunction indicator lamp on
Engine misfire or rough running, especially at idle
Cylinder 1 not firing, with a noticeable loss of power
Hard starting or extended cranking
Poor fuel economy
Possible fuel smell or raw fuel in the exhaust if the injector is stuck open

Possible causes

Injector wiring shorted to earth, chafed or damaged between the injector and the control unitlikely
Faulty cylinder 1 injector with an internal short or low coil resistancelikely
Corroded, loose or damaged injector connector or terminalspossible
Water ingress or contamination in the connector or loompossible
Faulty injector driver within the engine control unitrare
Wiring fault caused by a previous repair or aftermarket modificationrare

How to diagnose

Read all stored codes and freeze frame data, noting engine temperature, load and speed when the fault set, and check for other injector or misfire codes
Visually inspect the cylinder 1 injector connector, terminals and loom for damage, chafing, heat damage, corrosion or water
Check the injector connector is fully seated and the terminals grip properly, without forcing anything
Measure the injector coil resistance and compare it with the manufacturer specification for the engine
With the control unit and injector disconnected, test the wiring for a short to earth and for continuity, using the wiring diagram for the vehicle
Check the injector supply voltage at the connector with the ignition on, as the supply arrangement depends on the model and engine
Use a bidirectional test or a noid-type or scope check to confirm the control unit is producing a proper injector drive signal
Swap the injector with another cylinder, where design allows, to see whether the fault follows the injector, and clear the code to check it does not return

How to fix

Repair or replace damaged wiring, correcting any short to earth
Clean or replace the corroded or damaged injector connector and terminals
Replace the faulty injector and carry out any adaptation or coding the manufacturer requires
Dry out and seal the connector or loom, and fix the cause of water ingress
Repair or replace the engine control unit only after the wiring and injector have been proven good

Can I keep driving?

Medium severity

The car can usually be driven short distances, but a dead or leaking injector causes misfires and may wash oil from the bore or damage the catalytic converter. Have it checked soon and avoid heavy loads or long journeys until repaired.

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