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P0066 is a diagnostic trouble code (DTC) for "Air Assisted Injector Control Circuit or Circuit Low". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
Air Assisted Injector Control Circuit or Circuit Low
This code indicates that the powertrain control module (PCM) is detecting a voltage from the air assisted injector control circuit that is below specifications. When this low voltage is detected, the idle air/fuel mixture may not be within specifications and will therefore set off a Check Engine Light.
This code can be caused by the air assisted injector control wiring or connectors having a short or being damaged in some way. If the air assisted injector control valve is unplugged or has a bad connection, that can also cause this code. There is also an injector control relay that may have gone bad that could cause this code as well.
Symptoms of this code would include the Check Engine Light being illuminated, slight stumble or hesitation from the engine when the throttle is released, or the engine may die completely in very extreme cases.
The air assisted injector system works to better atomize the fuel during deceleration of the vehicle. If the voltage to the air assisted injector system is too weak to open and close the air assisted injector control valve, the air/fuel mixture may be too rich temporarily during deceleration. This is what would cause the stumble and hesitation. The Check Engine Light comes on due to the fact that this system is connected to the powertrain control module.
When diagnosing this issue, a mechanic might start with inspecting the air assisted injector system parts such as the air assisted injector valve, wiring, and vacuum hoses that are associated with this system for any faults such as shorted wiring, torn or frayed vacuum hoses, faulty injector valve, or bad electrical connections. This diagnosis would include using a digital multimeter to check voltage at specific points in the circuit to ensure they are within specification as well as a good visual inspection of all parts. Any faults that are found would be noted and repaired at the customer’s earliest convenience.
Common diagnostic mistakes that could be made during the repair of this issue could include replacing the fuel injectors or the air assisted injector valve without testing their functionality. Replacing any parts without first verifying that the are faulty would be a diagnostic mistake and is also very common.
This code would not be considered very serious due to the fact that it only affects the engine under certain conditions. It would be advised to resolve the issue as soon as possible, since driving the engine under abnormal conditions for a long period of time can cause internal engine damage. The best description for the seriousness of this code would be a minor problem that can get much worse if it is ignored for a long period of time.
Repairs that can fix the P0066 code would include:
If any of the system wiring is damaged, the most inexpensive way to resolve the issue would be to wrap electrical tape around the damaged portion of the wire as opposed to replacing the entire air assisted injector circuit wiring harness. Also, even if the vacuum lines are not the cause of this code to be set in the powertrain control module, it is a good idea to go ahead and replace them in the process of servicing this system as a preventative maintenance service.
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