Code 66

AIR INJECTION CONTROL CIRCUIT - DTC 66

The ECM looks for an incorrect internal circuit voltage that indicates the state of the air injection relay coil switching circuit. This internal voltage cannot be measured.

The ECM switches on the air injection pump by grounding the air injection relay coil circuit (85 pin). Air injection is enabled after engine start up and remains on until the coolant temperature reaches 95°F (34°C). On 1993 MY ON vehicles, air injection is enabled after each engine start for a mapped period. Air injection is disabled above 2500 rpm engine speed.

The ECM will flag DTC 66 if the air injection control circuit is open or short circuit.

Conditions Required For DTC 66 Flagging
Ignition - Ignition ON.
ECM internal circuit - Indicates that the air injection control circuit is open or short circuit.
Response time - 100 milliseconds.

Limp Home Default
None

Possible Faults
- Low battery voltage.
- Poor ECM power feed or ground connections.
- Short circuit or open circuit wiring from the ECM to the air injection relay.
- Short circuit or open circuit in ignition switched power supply to the air injection relay pin 86.
- Defective relay.

Diagnostic Notes
1. If the air injection pump is inoperative but DTC 66 is not flagged, investigate the air injection pump switched power supply (relay), air injection clutch circuit and the air injection pump mechanical condition.
2. If an air injection control circuit fault is present when the ignition is switched ON, both DTC 66 and 22 will be flagged.

Circuit Diagram

Control Circuit:

Control Circuit:

Flow Chart - DTC 66

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Flow Chart - DTC 66: