DTC P0066 – Air-Assisted Injector Control Circuit Low.

P0066 – Air Assisted Injector Control Circuit Low

Meaning:

The ECM has detected low voltage in the air-assist injector control circuit.

This system is used mainly in cold start to improve atomization by supplying air to the injector.

Common Causes

Electrical

Open circuit in air-assist injector wire (control/ground)

High resistance in connector or terminals (corrosion, loose pins)

Short to ground in harness

Faulty air-assist injector solenoid

Blown fuse / failed relay (if system uses one)

ECM driver fault (less common)

Mechanical

Stuck or clogged air-assist injector

Carbon buildup in injector air passage

Symptoms

Hard cold starting

Rough idle during cold start

Increased emissions

Poor fuel economy

MIL ON

Step-by-Step Diagnosis (For a Workshop)

1. Visual Inspection

Check wiring from ECM → air-assist injector.

Look for:

Damaged insulation

Pinched harness

Oil contamination on connector

Loose / bent pins

2. Check Connector Voltage

Key ON, engine OFF:

One wire should have battery voltage (12V) or 5–12V reference (depends on vehicle).

The other wire is ECM-controlled ground/driver.

If no voltage →

Check fuse

Check relay

Trace for open circuit

3. Check Control Circuit (ECM side)

Use a test light:

Connect test light to battery positive

Probe the ECM control wire while cranking or during cold start.

It should blink (pulsing ground).

If no pulsing ground →

Open circuit between ECM and injector

ECM driver fault (only after wiring confirmed)

4. Injector Resistance Test

Disconnect injector → measure resistance:

Typical range: 8–18 Ω (varies by vehicle).

If:

Open circuit → Replace injector

Too high resistance → Replace injector

Shorted (<1 Ω) → Replace injector

5. Check Air Passage / Mechanical Function

Remove air-assist injector if accessible

Clean carbon deposits

Verify air supply is not blocked

6. Clear Code & Perform Cold Start Test

After repair, monitor live data:

Air-assist injector duty cycle

ECM control voltage

Short/long fuel trims during cold start

Most Common Fixes

🌟 Repair damaged wiring

🌟 Clean connector pins

🌟 Replace faulty air-assist injector solenoid

🌟 Clean carbon-blocked air injector passages

🌟 Fix blown fuse or relay

🌟 Repair open/short to ground in harness

Welcome To Madurai Car Service💐🙏🏻.