What Is P0261?
P0261 is stored when the ECU detects a low voltage or short-to-earth condition on the cylinder 1 injector circuit. Unlike an open circuit fault, a low circuit fault means current is finding an unintended path to earth - through damaged wiring insulation or a shorted injector solenoid winding.
The result is that the cylinder 1 injector cannot fire correctly, producing a misfire. The ECU also detects the abnormal circuit behaviour and logs P0261. As with all injector faults, unburnt fuel entering the exhaust can damage the catalytic converter if the fault persists.
Common Symptoms
- Misfire on cylinder 1
- Engine management light on (may flash)
- Loss of power
- Rough idle and engine shake
- Fuel smell from exhaust
- Possible damage to catalytic converter if driven far
Common Causes
OBD Fault Code Plain English Guide
- 100 most common UK fault codes in plain English
- A severity rating for every code so you know what can wait
- Causes and next steps listed for each fault
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How to Diagnose P0261
Disconnect Injector and Recheck
Unplug the cylinder 1 injector connector and clear the fault code. If P0261 reappears with the connector unplugged, the short is in the wiring, not the injector. If it clears, the injector solenoid is shorted.
Test Injector Solenoid Resistance
Measure resistance across the cylinder 1 injector terminals. Near-zero resistance (well below 1 ohm on a petrol injector) indicates the solenoid winding is shorted internally - replace the injector.
Check Wiring for Short to Earth
With the connector unplugged, measure resistance between the signal wire and earth. Less than 1 ohm indicates a short to earth in the wiring. Inspect the harness for chafing, bare wires, or damage where it passes near the engine block or exhaust.
Inspect the Connector
Check the injector connector for bent pins that may be contacting the earthed engine body. Also check for moisture ingress - a wet connector can create a leakage path to earth.
Trace the Wiring Loom
If a wiring short is confirmed, systematically trace the cylinder 1 injector wiring from the connector back to the ECU. Use heat-resistant wire for any repair near the exhaust manifold.
Replace Injector if Solenoid is Shorted
If the solenoid itself is shorted, replace the injector. On diesel engines, enter the new injector trim code into the ECU after replacement.
Verdict
Disconnect the injector first and recheck - this isolates wiring faults from injector faults instantly. Short to earth in the wiring or shorted solenoid are the two most common causes.
P0264, P0267 and P0270 - Circuit Low On The Other Cylinders
P0261 has three siblings: P0264 (cylinder 2), P0267 (cylinder 3) and P0270 (cylinder 4). They all mean the same thing - the ECU sees the injector circuit for that cylinder pulled low when it should not be - and everything on this page applies to whichever cylinder your code names. A circuit-low code usually means a short to earth somewhere between the ECU pin and the injector, or an injector coil that has broken down internally.
The classic culprit on higher mileage engines is the loom chafing through where it runs across the rocker cover or clips to a bracket - the insulation wears, the wire touches metal, and the circuit reads low. Trace the harness for that cylinder with your fingers before buying parts; a rubbed-through wire is a five minute repair with heat shrink. An injector resistance check against a healthy neighbour settles the injector question: a coil reading well below its siblings has broken down.
If the low codes appear on every cylinder at once, stop chasing individual injectors - a shared earth fault or a failing driver stage in the ECU pulls the whole bank down together, and the fix lives at the common point, not at any one cylinder.
