21 Upstream O2S Stays at Center- (P 0134)

21 UPSTREAM O2S STAYS AT CENTER- (P 0134)





When the key is turned to the RUN position, the O2 sensor's output wire is biased inside the Powertrain Control Module (PCM) with a voltage of 0.45 volts. The PCM monitors the O2 sensor for a change in the biased voltage. As oxygen in the exhaust supply changes, the O2 sensor's output voltage changes. A voltage less than 0.45 volt indicates excessive oxygen in the exhaust. A voltage greater than 0.47 volt indicates insufficient oxygen in the exhaust. The PCM uses the information from the O2 sensor to assist in adjusting the air/fuel ratio to a stoichiometric ratio.

ENABLING CONDITIONS
- Engine must have been running for at least two minutes
- Engine temperature must be greater than 77°F

The Malfunction Indicator Lamp (MIL) illuminates and a Diagnostic Trouble Code (DTC) is stored if, after the enabling conditions have been met, the voltage from the O2 sensor does not move from the bias voltage of 0.45 volt.

This malfunction could possibly be caused by problems with any of the following:

- O2 sensor
- O2 sensor wiring or related connections (open-circuited)
- PCM