P0138

Diagnostic Chart:

Schematic:

The rear Heated Oxygen Sensors (HO2S) are used to determine the oxygen storage capability of the pup converter. Rear O2 diagnostics will run after the sensor has been active for more than 80 seconds, and the catalyst temperature is greater than 600°C (1112°F). If the ECM detects an excessively high signal voltage, this DTC will set.

DTC PARAMETERS
This DTC will set when:
^ The sensor signal voltage greater than 1.08 volts for longer than 5.1 seconds
^ Engine is running
^ Catalytic temperature less than 700°C (1292°F)
^ Battery voltage greater than 11.03 volts

DTC P0138 is a (type B) DTC

DIAGNOSTIC AIDS
To locate an intermittent problem use Scan tool to monitor HO2S Bank 1 Sensor 2 voltage with engine idling at normal operating temperature.

Wiggling wires while monitoring HO2S Bank 1 Sensor 2 voltage may locate area where a short to voltage exists.

If a HO2S Bank 1 Sensor 1 DTC is also set, diagnose it first. A failed HO2S Bank 1 Sensor 1 may create a lean engine running condition which set the HO2S Bank 1 Sensor 2 DTC.

Review failure record information to check if vehicle was running lean in power enrichment (TP angle greater than 75%, HO2S Bank 1 Sensor 1 less than 0.8) when the DTC was set. If so, check for a possible rich condition.