Fault code P0066 is called “Air Assisted Injector Control Circuit or Circuit Low” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.
Technical description and explained code P0066
To improve combustion, especially when the engine is cold, some automakers have introduced an air-assisted fuel injection system. The system draws air from the intake port in front of the throttle. It is then routed to the fuel injectors through hoses, tubing, or intake manifold passages.
Fuel is injected in the usual manner using electrical pulses from the engine control module (ECM) into a small chamber. There, a vacuum from the intake manifold draws air into the chamber.
The air is swirled along with the fuel, resulting in better atomization. The fuel-air mixture then enters the cylinder, where it is fully atomized for combustion.
The ECM increases the air supply when the engine is cold and running at idle or low speed with low load. At higher temperatures and when the throttle is open, the air support system does not work.
The ECM module uses air-fuel ratio (AFR) sensor feedback to control the air supply.
If the control module detects that the fuel injector system with an additional air channel has a low signal level in the circuit. It is letting too much air into the system or, conversely, not enough. Then fault code P0066 will be set, and the MIL warning light on the instrument panel will illuminate.
This code is usually set when a sensor or other component is not operating within the range that the powertrain control module (PCM) expects to see.
Symptoms of vehicle malfunctions
The main signal that an error P0066 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- The “Check Engine” control lamp on the control panel will illuminate (the code will be stored as a fault).
- Fuel or idle adjustment codes may also be present.
- Poor cold engine starting.
- Jerking/missing ignition at idle during warm-up cycle.
- Poor acceleration while engine is cold.
- Increased fuel consumption.
In most cases, the error P0066 affects cold start of the engine, after warming up there are usually no symptoms. Therefore, the degree of severity can be considered moderate.
Factors that can cause this error code
The error code P0066 can mean that one or more of the following problems have occurred:
- Fuel injector with auxiliary air channel is defective.
- The air nozzle control solenoid valve is defective.
- Vacuum leak inside the injector or in the hoses.
- Vacuum hoses are clogged.
- Damage to electrical wires, contacts, or connectors.
- Blown fuse or relay.
- Sometimes the cause is a faulty PCM module.
How to fix or reset OBD-2 code P0066
Some suggested steps for troubleshooting and fix the error code P0066:
- Connect the OBD-II scanner to the vehicle’s diagnostic connector and read all stored data and error codes.
- Clear any other errors that may be present before continuing to diagnose code P0066.
- Disconnect the vacuum hoses from the air nozzle control solenoid valve and blow them out with compressed air to make sure the hoses are not clogged.
- The hoses should also be checked for leaks.
- Check the air nozzle control solenoid valve.
- Test for voltage and ground signals on the solenoid valve.
- Visually inspect electrical wires and connectors.
- If necessary, repair or replace any wires that are shorted, broken, damaged, or corroded.
Diagnose and repair of problems
Before resolving error P0066, it is necessary to read the Technical Service Bulletins (TSB). An updated ECM firmware may be available to resolve the problem.
If the control valve has been replaced, the ECM may need to be re-trained on the new valve.
Check the control valve
Check that the control valve is properly connected. Check the connector for corrosion or water intrusion, and repair if necessary.
Disconnect the air hoses from the control valve and turn on the valve using an active diagnostic tool test or by applying battery voltage. Make sure air is flowing when the valve is activated. Make sure no air passes when the valve is off, clean or replace if necessary.
Checking the vacuum
Make sure the rubber hoses and tubing are in good condition, without cracks or kinks. Make sure metal tubing is not bent or jammed, repair if necessary.
Blow low pressure air into the system and check for air coming out of the intake or exhaust port. If air is escaping elsewhere, locate and replace the faulty tube or hose.
Some air may escape from the fuel injectors, but this is not common.
Sensor check
Because the PCM controller monitors the auxiliary air pressure with AFR sensors. If the sensor malfunctions, it may generate an erroneous code related to the auxiliary air channel injector.
If you are able to perform an active fuel correction check, you can check how fast the AFR sensor responds.
On which vehicles does this problem occur most frequently
Fault code P0066 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
- Audi
- Chevrolet
- Dodge
- Ford
- Honda
- Jaguar
- Kia (Sorento)
- Mercedes-Benz
- Peugeot (307)
- Subaru (Impreza, Legacy)
- Toyota
- Volkswagen
Fault code P0066 can sometimes be found with other errors. The most common are the following: P0065, P0067.
