Fuel and air

P0066 — Air Assisted Injector Control Circuit Low

Severity: medium Drive with care, to a shop

What P0066 means

Some engines use air assisted injectors, where an air supply helps atomize the fuel, especially on a cold engine. The ECM drives the injector or its air valve through a dedicated circuit and monitors the voltage. P0066 sets when that voltage is lower than expected or the circuit does not respond as commanded. Wiring, connectors, the valve or injector are the usual culprits, and an ECM driver fault is less common.

Symptoms

  • Check Engine light on
  • Rough or unstable idle
  • Hard starting or poor running when cold
  • Hesitation or stumble on acceleration
  • Increased fuel consumption
  • Possible misfires

Possible causes

  1. Damaged or corroded wiring and connectors in the air assisted injector circuit
  2. Control wire shorted to ground
  3. Faulty air assisted injector or air solenoid valve
  4. Internal driver fault in the ECM
  5. Vacuum or intake leaks affecting operation
  6. Skewed MAP or airflow sensor readings confusing mixture control

How to diagnose

  1. Read all codes and freeze frame data to see when the fault sets
  2. Inspect the injector and valve harness and connectors for chafing, corrosion and oil contamination
  3. Check power, ground and the control signal from the ECM at the connector
  4. Measure the valve or injector coil resistance and compare to specification
  5. Test the circuit for a short to ground and for open circuits with the connector unplugged
  6. Review fuel trims and cylinder balance
  7. Check fuel pressure and look for intake air leaks
  8. If wiring and the actuator are good, test the ECM driver

Common fixes

  • Repair the wiring or replace damaged connectors
  • Replace the faulty air assisted injector or air valve
  • Fix vacuum and intake leaks
  • Replace or reprogram the ECM if a driver fault is confirmed
  • Clear the code and confirm it does not return on a test drive

Questions and answers

What does P0066 mean?

It is a generic OBD-II code: the ECM sees low voltage or a malfunction in the air assisted injector control circuit. It usually comes down to wiring, the valve or the injector.

Can I drive with a P0066 code?

Briefly, yes, but the engine may run roughly and use more fuel. Don't put off diagnosis, or you risk misfires.

How do I find the cause of P0066?

Start by inspecting the wiring and connectors, then measure the valve or injector resistance and check the ECM signal. Replacing the ECM is the last step.

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.