P0066 – Air Assisted Injector Control Circuit or Circuit Low
The P0066 diagnostic trouble code indicates that the Engine Control Module (ECM) has detected a low voltage or electrical fault in the Air Assisted Injector Control circuit. This system is used on certain vehicles to improve fuel atomization by supplying pressurized air to the fuel injectors.
When the ECM detects that the control circuit voltage is lower than the expected range, it stores the P0066 code and illuminates the Check Engine Light.
Common Symptoms
- Check Engine Light ON
- Rough idle
- Reduced engine performance
- Increased fuel consumption
- Higher exhaust emissions
Common Causes
- Faulty air-assisted injector control solenoid
- Short to ground in the control circuit
- Open or damaged wiring
- Loose or corroded electrical connector
- Rarely, a faulty ECM
Basic Diagnosis
Inspect the wiring harness and connectors for damage or corrosion. Verify the power supply and ground, check for a short to ground in the control circuit, and use a scan tool to command the system on and off. Repair wiring faults or replace the control solenoid if necessary.
Diagnostic Note: The Air Assisted Injector system is not installed on every vehicle. Component location, circuit design, and diagnostic procedures vary by manufacturer. Always consult the factory service manual and wiring diagram before testing.