P0270 — Cylinder 4 Injector Circuit Low

What Is P0270?

P0270 is stored when the ECU detects a low voltage or short-to-earth condition on the cylinder 4 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 4 injector cannot fire correctly, producing a misfire. The ECU also detects the abnormal circuit behaviour and logs P0270. As with all injector faults, unburnt fuel entering the exhaust can damage the catalytic converter if the fault persists.

Common Symptoms

Misfire on cylinder 4
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

Short to earth in the cylinder 4 injector wiring — damaged insulation

Shorted injector solenoid winding on cylinder 4 injector

Damaged connector with bent pin contacting earthed body

Chafed wiring near engine block or exhaust manifold

Water ingress into connector causing leakage current to earth

ECU driver fault (rare — after ruling out all wiring faults)

How to Diagnose P0270

Disconnect Injector and Recheck

Unplug the cylinder 4 injector connector and clear the fault code. If P0270 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 4 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 4 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.

Do Not Continue DrivingA misfiring cylinder causes unburnt fuel to enter the exhaust, overheating and potentially destroying the catalytic converter. Do not drive long distances with P0270 active — the repair cost of a catalytic converter exceeds that of an injector.

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.