1221/1222 - Oxygen Sensor

Engine Management:

1. If a code 1221 or 1222 is present, cancel the DME fault code memory after noting all other existing codes.
2. Start the engine and warm it up to normal operating temperature. Drive the vehicle varying the load conditions. If the "Check Engine" light does not illuminate the problem is intermittent. If the "Check Engine" light does illuminate and a fault code 1221 or 1222 is present continue with step 3.

3. With the ignition switch in the OFF position, disconnect the oxygen sensor in-line connector C140.
4. Turn the ignition switch to the run position and make the following voltage measurements at connector C140 (male side).

^ Black wire (terminal 2) and ground = approx. 0.65 volts.
^ Black (terminal 2) and brown wire (terminal 1) = approx. 0.45 volts.

5. Turn the ignition switch OFF and measure between:

^ Black wire (terminal 2), and brown wire (terminal 1) = 0 volts.
^ If all voltages are correct, continue with step 6.
^ If any voltages are incorrect, check wires to terminals 70 and 71 of the DME control unit (harness disconnected), for an open or short to ground. If the wires are OK, the DME control unit may be defective.

6. Check the following items for operation and repair or replace as necessary. If no problems are found continue with step 7.


RUNNING RICH
- Engine oil diluted with fuel
- Operation of the purge valve
- Operation of the charcoal canister
- Operation of the DME main relay
- Operation of the fuel pump relay
- Stuck open injectors
- Operation of the of the fuel pressure regulator

RUNNING LEAN
- Air leak at crankcase vent hose
- Air leak at the idle control valve hoses
- Air leak at the rubber boot between the air flow meter and throttle housing
- Air leak at injector rubber sealing rings
- Clogged injectors
- Insufficient fuel pressure
- Bad fuel (water in fuel)

7. With the ignition switch OFF, install a new oxygen senor.
8. Reconnect harness connectors, start the engine, and warm it up to normal operating temperature. Drive the vehicle varying the load conditions. If the "Check Engine" light does not illuminate, retain the new oxygen sensor. If the "Check Engine" light does illuminate and a fault code 1221 or 1222 is present the DME control unit is defective.