Air Assisted Injector Control Circuit or Circuit Low
P0066 indicates the engine control module has detected a voltage or signal problem in the air-assisted fuel injector control circuit. This code triggers when the ECM measures an abnormally low signal in the injector control circuit, preventing proper fuel atomization and distribution to the cylinders.
What You Might Notice
- Hard starting, especially in cold conditions
- Engine misfiring or running rough
- White or blue smoke from exhaust
- Poor fuel economy
- Reduced engine performance under acceleration
Most Common Causes
- 1
Damaged or loose wiring harness
Broken, corroded, or disconnected wires in the fuel injector control circuit prevent proper voltage signal transmission to the ECM. This is the most common cause and should be inspected first.
- 2
Faulty fuel injector
An internal failure or wear in the air-assisted injector itself can cause it to draw incorrect current, triggering a low circuit voltage condition at the ECM.
- 3
Defective injector control driver in ECM
A failed transistor or control circuit inside the engine control module may be unable to properly drive or modulate the injector signal.
- 4
Vacuum leak at injector assembly
A leak in vacuum lines connected to the air-assisted injector can affect spray pattern and cause signal anomalies detected by the ECM.
How to Diagnose It
- 1
Check Damaged or loose wiring harness — Broken, corroded, or disconnected wires in the fuel injector control circuit prevent proper voltage signal transmission to the ECM. This is the most common cause and should be inspected first.
- 2
Check Faulty fuel injector — An internal failure or wear in the air-assisted injector itself can cause it to draw incorrect current, triggering a low circuit voltage condition at the ECM.
- 3
Check Defective injector control driver in ECM — A failed transistor or control circuit inside the engine control module may be unable to properly drive or modulate the injector signal.
- 4
Check Vacuum leak at injector assembly — A leak in vacuum lines connected to the air-assisted injector can affect spray pattern and cause signal anomalies detected by the ECM.
How to Fix It
- 1
Inspect and repair wiring harness
Visually inspect all wiring connections to the fuel injector and control circuit for corrosion, damage, or loose terminals. Repair or replace damaged wires and ensure all connections are secure.
- 2
Replace fuel injector
If wiring is confirmed good, remove and test the fuel injector for proper electrical resistance and spray pattern. Replace the injector assembly if it fails testing.
- 3
Check and seal vacuum lines
Inspect all vacuum hoses connected to the air-assisted injector system for cracks, splits, or loose connections. Replace any damaged hoses and ensure tight fitting connections.
- 4
Test or replace ECM
If all external components are verified good, the ECM driver circuit may be faulty. Have the module tested by a specialist or replace if diagnosis confirms internal failure.
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