Fuel and air

P0271 — Cylinder 4 Injector Circuit High

Severity: medium Drive with care, to a shop

What P0271 means

The engine control module switches the cylinder 4 injector on and off and monitors the voltage and current in its circuit. P0271 sets when the signal is higher than expected, which can come from an open circuit, a short to power, a failed injector or a faulty driver inside the module. The cylinder may then get the wrong amount of fuel or none at all.

Symptoms

  • Check Engine light on
  • Rough or unstable idle
  • Loss of power and sluggish acceleration
  • Misfire on cylinder 4
  • Higher fuel consumption
  • Hesitation under load

Possible causes

  1. Faulty cylinder 4 injector (open or failing coil)
  2. Damaged wiring or corroded injector connector
  3. Circuit shorted to battery voltage
  4. Failed injector driver in the ECM
  5. Electrical supply problems such as voltage spikes, poor grounds or a bad relay
  6. Poor previous wiring repair

How to diagnose

  1. Scan for codes and freeze frame data, and look for other injector or misfire codes
  2. Inspect the cylinder 4 injector connector and harness for chafing, moisture, corrosion or heat damage
  3. Measure injector coil resistance and compare it with the spec and the other injectors
  4. Check for power and the control pulse at the connector with a meter or scope
  5. Test the wire to the ECM for opens and shorts to voltage
  6. Check ECM power, fuses, relays and grounds
  7. Review fuel trims and cylinder balance, and check fuel pressure
  8. If wiring and injector are good, suspect the ECM driver

Common fixes

  • Replace or clean the cylinder 4 injector if it is faulty
  • Repair damaged wires or replace the connector or terminals
  • Fix any short to power in the harness
  • Correct power or ground problems
  • Repair, reprogram or replace the ECM if the driver has failed

Questions and answers

What does P0271 mean?

It means the cylinder 4 injector circuit shows a high signal. The cause can be the injector, the wiring or the control module.

Can I drive with P0271?

Only for a short trip to get it diagnosed. Misfires waste fuel and can damage the catalytic converter.

What should I check first?

Start with the connector and wires at the cylinder 4 injector, then test injector resistance and the control signal from the ECM.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.