P0146

Circuit Description

The PCM provides a 0.45 volt reference to the oxygen sensor on CKT 1668. When the Oxygen Sensor reaches operating temperature it will generate a counter voltage that will vary based on the amount of oxygen in the exhaust. The post-converter heated oxygen sensor is located in the exhaust after the catalytic converter. A lean exhaust will generate a low voltage and cause the 0.45 reference to move lower. A rich exhaust will generate a high voltage and cause the 0.45 reference to move higher. If the oxygen sensor cannot respond under the test conditions and generate a voltage greater than 0.609 volt or less than 0.307 volt, it will set a DTC P0146. Possible causes of DTC P0146 are:

^ Open in CKT 1668 or 1669.
^ Short to voltage on CKT 1668 or 1669.
^ Oxygen sensor that malfunctions.
^ An ineffective oxygen sensor heater.
^ A poor HO2S ground.

Conditions for Running the DTC

^ DTCs P0117, P0118, P0122 and P0123 not set.
^ Coolant temperature 75°C (167°F) or greater.
^ Throttle between 2.2 and 81.6 degrees.
^ (Calculated) Throttle position switch open.
^ Engine speed between 800 and 3000 RPM.

Conditions for Setting the DTC

Oxygen sensor voltage stays between 0.307 volt and 0.609 volt for 250 out of 300 seconds, oxygen sensor voltage not toggling.

Action Taken When the DTC Sets

^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) after two consecutive drive trips that the diagnostic runs and fails.
^ The PCM will record operating conditions at the time the DTC sets. This information will be stored in the Freeze Frame and Failure Records.
^ A first failure of this DTC will store in Last Test Failed but not History.

Diagnostic Aids

Notice: Do not solder heated oxygen sensor wires. Soldering the wires will result in the loss of the air reference to the sensor.

A loose HO2S or one with a poor exhaust ground may cause this DTC to set. Before replacing an HO2S always check the resistance of the sensor ground. On a COLD engine, measure the resistance between the HO2S low circuit and the PCM ground at the PCM connector. If the resistance measures more than 500 ohms (typically less than 50 ohms), remove the sensor and check for corrosion at the HO2S sensor threads. Clean the HO2S sensor threads, apply a coating of anti-seize compound (5613695 or equivalent) and torque the HO2S sensor to the proper torque. Recheck HO2S ground resistance and replace any sensor with resistance above 500 ohms.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

2. Voltage on the scan tool should fluctuate above 0.6 volt and below 0.3 volt. If voltage remains above 0.6 volt, check the Post HO2S High circuit for a short to voltage. If voltage remains below 0.3 volt, check the Post HO2S High circuit for a short to ground.
3. Measuring voltage with a voltmeter will isolate a sensor problem from a PCM wiring problem.