1, 2 and 3 Digit Codes: 129

Scan Tool 129 (MIL 21):

Trouble Code Number
- Scan tool 129
- General scan tool P0140
- MIL 21

Fault Message
- Downstream O2S Stays at Center

Background
- Sensor output voltage is checked.
- If voltage stays at center instead of switching, an open circuit is likely.

Range of Check
- 2 or more minutes after starting engine
- Engine coolant temperature: More than 80°C (176°F).

Set Condition
- Neither rich nor lean condition is detected from the rear bank downstream heated oxygen sensor input. (Voltage is 0.5 volts for 1.5 minutes)

Probable Cause
- Downstream heated oxygen sensor failed
- Wiring harness and connectors failed
- PCM failed