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Diagnostic Trouble Code: 021
Diagnostic Trouble Code Name: Rear Defrost Request Switch Circuit
Vehicle Make: Chevrolet
Vehicle Model: Tosca (V250)
Diagnostic Code Entered By: ZerOne
Diagnostic Code Entered On: Wed Oct 06, 2010 11:00 pm
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Please Note: The DTC Information provided has been randomly generated.
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Diagnostic Trouble Code Description:
O2 Sensor Circuit High Volt
Possible Sensor Faults
ECM
Possible Related Diagnostic Trouble Codes
DTCP0138 or P0158
Circuit / System Description
Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The engine control module (ECM) supplies the HO2S with a reference, or bias, voltage of about 450?mV. When the engine is first started the ECM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000?mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream. If the ECM detects an HO2S voltage that stays above a specified value, DTC?P0138 sets for HO2S bank?1 sensor?2, or DTC?P0158 sets for HO2S bank?2 sensor?2.
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