1, 2 and 3 Digit Codes: 103

Scan Tool 103 (MIL 21):

Trouble Code Number
- Scan tool 103
- General scan tool P0135
- MIL 21

Fault Message
- Upstream HO2S Heater Failure

Background
- The PCM continues to monitor this system after the key is OFF.
- The PCM waits some periods to allow the heated oxygen sensor to cool.
- Once the PCM calculates that the heated oxygen sensor is cooled, it energizes the MFI relay (ASD relay) and tests for the rear bank upstream heated oxygen sensor operation.

Range of Check
- 5 seconds or more after turning the ignition switch to OFF.
- Battery positive voltage: 10 V or more
- The heated oxygen sensor output line voltage rises by 0.49 V or more within 144 seconds after turning the ignition switch to OFF.
- The initial rise of the output line voltage is less than 1.57 V.

Set Condition
- Heated oxygen sensor circuit does not show the appropriate decrease of voltage during the test.

Probable Cause
- Upstream heated oxygen sensor heater open
- Wiring harness and connectors failed