Faulty cylinder 4 injector with a shorted or low-resistance coil; Injector wiring chafed or shorted to earth between the injector and the control unit; Corroded, loose or damaged injector connector or terminals; Water ingress or contamination in the harness or connector; Fault in the injector driver circuit inside the engine control unit; Harness damage elsewhere affecting the injector supply or control line, depending on model.

P0270

Cylinder 4 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)
70: FaultThe specific fault in that area

What it means

P0270 is a generic powertrain code meaning the engine control unit has detected a low signal or low voltage in the control circuit for the cylinder 4 fuel injector. The control unit monitors the injector circuit and sets the code when the voltage or current does not match what it expects, which usually points to a short to earth or a fault in the injector driver circuit. The 'A' designation and exact circuit layout vary by manufacturer and engine, so wiring diagrams for the specific model are needed.

Symptoms

Engine misfire or rough running, especially on cylinder 4
Malfunction indicator lamp on
Hesitation or reduced power
Rough idle or hard starting
Poor fuel economy
Engine may run in a reduced performance mode

Possible causes

Faulty cylinder 4 injector with a shorted or low-resistance coillikely
Injector wiring chafed or shorted to earth between the injector and the control unitlikely
Corroded, loose or damaged injector connector or terminalslikely
Water ingress or contamination in the harness or connectorpossible
Fault in the injector driver circuit inside the engine control unitrare
Harness damage elsewhere affecting the injector supply or control line, depending on modelpossible

How to diagnose

Read all stored and pending codes and note the freeze frame data, including engine load, temperature and rpm when the fault set
Check for other injector or misfire codes to see whether the fault is isolated to cylinder 4
Visually inspect the cylinder 4 injector connector and the surrounding harness for chafing, heat damage, corrosion and poor terminal tension
Measure the cylinder 4 injector coil resistance and compare it with the manufacturer's specification for that engine
With the connector unplugged, check the control wire for a short to earth and for continuity back to the control unit using the wiring diagram
Check the injector supply voltage and earth at the connector with the ignition on
Monitor the injector operation with a suitable test method, such as a noid light or a scope waveform, while cranking or running
If wiring and the injector test fine, have the control unit driver circuit assessed according to the manufacturer's procedure

How to fix

Replace the cylinder 4 injector if its resistance or operation is out of specification
Repair or replace damaged wiring, fixing any short to earth, and secure the harness away from heat and sharp edges
Clean or replace corroded connectors and terminals
Dry out and seal the harness or connector if water ingress is found, and replace affected parts
Repair or replace the engine control unit only after all wiring and injector faults are ruled out and as the manufacturer directs
Clear the code and road test to confirm it does not return

Can I keep driving?

Medium severity

The car can usually be driven short distances, but a dead or misfiring cylinder can cause rough running and may overload the catalytic converter with unburnt fuel. Get it checked soon and avoid heavy loads or long journeys.

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