Downstream HO2S Stays at Center

Code Number
Scan tool 129
General scan tool P0140
MIL 21

Description
Downstream HO2S Stays at Center

Probable Cause
- Heated oxygen sensor (rear) failed
- Sensor signal circuit open
- PCM failed

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

Range of Check
- 2 minutes after starting engine
- Engine coolant temperature: More than 8O° C (176° F)

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





Diagnosis