OBD-II trouble code
P0066: Air Assisted Injector Control Circuit or Circuit Low
SAE J2012 APR2002 names this air assisted injector control circuit or circuit low. The title covers more than one electrical result. Identify the hardware on this engine before you buy a valve. Low still needs a short-to-ground test and a short-to-power test.
Quick facts
- System
- Powertrain
- Category
- Fuel Injectors
- Severity
- Low severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $125 – $183 (check engine light diagnosis, labor only; air-assist injector valve replacement not priced)
- DIY difficulty
- Intermediate DIY
Browse every code in P0001–P0099, or start from the full code library.
What does P0066 mean?
SAE J2012 APR2002 names P0066 Air Assisted Injector Control Circuit or Circuit Low. P0065 is range/performance and P0067 is circuit high. The SAE row itself uses both "circuit" and "circuit low." That is the title. It is not a finding that every manufacturer reports the fault differently, and it is not permission to treat the code as whatever the scan tool's generic text says when this engine has no air-assist parts.
Open the service information. Some engines use one on/off solenoid. Some modulate a valve. Some have no separate valve because the passages are in a casting. The test and the part follow that drawing. A generic catalogue is a poor guide in this corner because the hardware is uncommon.
If the diagram shows no air-assist hardware, stop. Re-read the code with equipment that displays the manufacturer's description before you search for a system the engine does not have. This page does not have an example of a manufacturer reusing P0066 for an unrelated component.
Where a solenoid is fitted, circuit or circuit low can be an open the monitor did not classify, a short to ground, or a connection that has gone high-resistance. With the valve unplugged and the module disconnected, check the control wire for a short to ground and, with the ignition on and both ends open, for voltage that would mean a short to power. Measure the winding against the resistance this procedure prints. No ohm figure is stated here.
Command the valve with a scan tool. Do not apply battery voltage to the connector unless the procedure names the terminals. The engine can be driven. Cold-running quality is the complaint this system can cause. There is no emissions percentage on this page.
Common causes
- No air-assist hardware on this engine, and the generic title was followed anyway
- A short to ground in the control wire, with the valve and the module disconnected
- An open in the control circuit
- A corroded or loose connector at the valve this diagram shows
- A winding outside the resistance this procedure prints
- The wrong valve, with a different winding or pinout
- The module driver, concluded after the wiring and the winding pass
Symptoms
- Check engine light with P0066
- P0065 stored as well, which is the performance test
- No air-assist parts visible, which means stop and confirm the code
- A cold idle complaint, if this engine uses the system for cold running
- No complaint once the engine is warm
Diagnostic steps
- 1.Find the hardware in the service information: on/off solenoid, modulated valve, or passages in a casting. Do not order a valve the diagram does not show.
- 2.If the engine has none of that hardware, re-read the code with a tool that shows the manufacturer's description.
- 3.Locate the connector from the diagram, not from a catalogue illustration.
- 4.Inspect the connector for heat damage, spread terminals, and corrosion before you unplug it for the last time.
- 5.Ignition off. Measure winding resistance against the printed spec. No number is given here.
- 6.Valve disconnected and module disconnected: control wire to ground for a short to ground. Ignition on, both ends open: voltage on the control wire for a short to power.
- 7.Confirm the supply and the ground the diagram names. Check the ground under load, not with a continuity beep alone.
- 8.Command the valve with a scan tool and watch the circuit. Do not power the solenoid from the battery unless the procedure names the pins.
- 9.Wiggle the harness with the circuit monitored and the vehicle stationary.
- 10.After repair, run the cold-start enable this chart prints.
Repair cost
$125 – $183 (check engine light diagnosis, labor only; air-assist injector valve replacement not priced)
P0066: No RepairPal parts-and-labor price for an air-assist valve was found. The printed pair is RepairPal check-engine-light diagnosis only, updated 3 September 2026, $125–$183, labor only. A valve, a hose, passage cleaning, and an injector are outside it and need a quote for this engine. RepairPal's $317–$409 fuel-pressure-regulator job is a rail or line regulator after depressurizing. It is not this valve and is not included in the pair. RepairPal's air-injection control valve average, $613–$767, is the secondary-air valve between the air pump and the exhaust. That is not an air-assisted injector valve, so it is not used here. YourMechanic lists a P0065 check-engine diagnostic at $154.99, with $50 credited toward the repair. That is diagnosis, not the valve. RepairPal's air-injection control solenoid average, $144–$175 on 3 September 2026, is mounted at the air pump or on the valve between the pump and the exhaust manifold. That is secondary air, not an air-assisted injector valve, so it is not used here. No parts-plus-labor total for the air-assisted injector valve was found.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with air-assisted injection system service preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.