P0066

What it means

P0066 is the generic code for a low signal in the air assisted injector control circuit. The engine control unit monitors the driver circuit for the air assist injector (or air assist control valve) and sets the code when the voltage or current is lower than expected for the commanded state. Air assisted injection is uncommon, so the layout and the circuit it monitors depend on the vehicle and engine.

Symptoms

• Engine warning light on
• Rough idle or unstable idle, especially when cold
• Hesitation or poor throttle response
• Hard starting or extended cranking
• Poor fuel economy
• Possible misfire or increased exhaust smoke

Possible causes

• Wiring fault in the air assist injector or valve control circuit, such as a short to earth or chafed insulationlikely
• Corroded, loose or damaged connector at the injector, valve or control unitlikely
• Faulty air assist injector or air assist control valve with an internal short or low coil resistancelikely
• Low or unstable supply voltage or poor earth to the circuit, from a weak battery or bad earth connectionpossible
• Blocked or leaking air assist passage or supply causing the monitored circuit to read incorrectlyrare
• Faulty driver stage inside the engine control unitrare

How to diagnose

1. Read all stored and pending codes and note the freeze frame data, including engine temperature, load and battery voltage, and check for other injector or misfire codes.
2. Look up the wiring diagram and component layout for the specific model and engine, as air assist systems differ between applications.
3. Inspect the wiring and connectors for the air assist injector or valve for chafing, heat damage, water ingress, corrosion and pushed-back pins.
4. Check battery condition and charging voltage, and inspect the main earth connections.
5. Measure the resistance of the injector or valve coil and compare it with the manufacturer's specification.
6. With the ignition on, check the supply voltage at the connector, then test the control wire for a short to earth and for continuity back to the control unit.
7. Command the injector or valve using the scan tool's active test, if available, and check that it operates and the signal switches correctly.
8. Only if the wiring and component test good, check the control unit driver and for any applicable software updates from the manufacturer.

How to fix

• Repair or replace damaged wiring, correcting any short to earth or open circuit.
• Clean, repair or replace corroded or damaged connectors and terminals.
• Replace the faulty air assist injector or control valve with a correct part for the engine.
• Restore correct battery condition and repair poor earth connections.
• Clear any blocked air passages, then clear the code and road test to confirm it does not return.
• Repair or replace the engine control unit only after all other causes have been ruled out, following the manufacturer's procedure.

Can I keep driving?

Nearby codes

• P0065GenericAir Assisted Injector Control Range/Performance
• P0067GenericAir Assisted Injector Control Circuit High