What Does P0066 Mean?
The ECM has detected a low voltage or low current condition in the air-assisted injector control circuit. This could be an open circuit, a short to ground, or a failed control solenoid that is preventing the air-assist system from activating. Without air assistance, fuel atomization will be degraded, particularly during cold starts. The driver may notice rough idle, misfires on cold start, and increased emissions.
Common Causes
35%
Failed air-assist control solenoid (open circuit internally)
28%
Open or broken wire in the air-assist control circuit
20%
Corroded or disconnected connector at the air-assist solenoid
10%
Blown fuse in the air-assist control supply circuit
7%
ECM internal driver circuit open/failure
Diagnostic Steps
1
Check the fuse for the air-assist injector control circuit. Replace if blown and investigate for a short before re-energizing the circuit.
2
Disconnect the air-assist control solenoid and measure coil resistance. Compare to spec (typically 10-40 ohms). An open circuit (infinite resistance) means the solenoid is failed.
3
Verify battery voltage is present at the solenoid supply wire with key on engine off. No voltage indicates an open in the power supply path.
4
Inspect the solenoid connector for corrosion, backed-out pins, or physical damage. The solenoid is typically mounted in the engine bay where it is exposed to heat and moisture.
5
If voltage and solenoid are good, check the control (ground) wire from the solenoid connector back to the ECM. Measure resistance — should be under 1 ohm. An open here means the ECM can't complete the circuit.
Estimated Repair Cost
$150 - $600
Parts + labor, varies by vehicle and location
The ECM has detected a low voltage or low current condition in the air-assisted injector control circuit. This could be an open circuit, a short to ground, or a failed control solenoid that is preventing the air-assist system from activating. Without air assistance, fuel atomization will be degraded...
The most common cause of P0066 (Air Assisted Injector Control Circuit or Circuit Low) is: Failed air-assist control solenoid (open circuit internally)
Typical repair costs for P0066 range from $150 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive but cold-start quality will be poor. Fuel atomization will rely solely on injector pressure without air assistance. Higher emissions during warmup and possible rough idle. No immediate safety concern. Repair within 2-3 weeks.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0066 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel System
Difficulty
Type
Generic (SAE)
Recommended Tools
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