P0146

CIRCUIT DESCRIPTION
The VCM supplies a voltage of approximately 0.45 volts (450 mV) between the HO2S High and the HO2S Low circuits.

If this voltage is measured using a 10 megohm digital voltmeter, the voltage may read as low as 0.32 volt. The Heated Oxygen Sensor (HO2S) varies the voltage within a range of about 1.0 volt (1000 mV) if the exhaust is rich to as low as 0.10 volt (10 mV) if the exhaust is lean.

The VCM monitors the Heated Oxygen Sensor (HO2S) activity for 100 seconds after a Closed Loop. During the monitor period, the VCM counts the number of times that the HO2S switches from rich to lean and from lean to rich and adds the amount of time it took to complete all switches. With this information, an average time for all switches can be determined. If the average time to switch is too slow, a DTC P0146 sets.

When HO2S temperature is below 360°C (600°F), the sensor will not produce any voltage. The sensor will also behave like an open circuit. This will result in an Open Loop operation.

The HO2S heater provides for a faster sensor warm-up which allows the sensor to become active in a shorter period of time and remain active during a long extended idle. The DTC P0146 determines if the HO2S is functioning properly by checking its response time. This DTC is a type B DTC.

CONDITIONS FOR SETTING THE DTC
The following conditions will set the DTC:

^ No TP sensor DTCs.
^ No Evaporative Emissions (EVAP) DTCs.
^ No IAT sensor DTCs.
^ No MAP sensor DTCs.
^ No ECT sensor DTCs.
^ No MAF sensor DTCs.
^ No intrusive test in progress.
^ No device controls active.
^ The system voltage measures at least 9.0 volts.
^ The engine run time is greater than 2 minutes.

HO2S Sensor Open Test Enable

^ The engine run time is greater than 2 minutes.
^ A Closed Loop exists.
^ The DTC P0146 (HO2S heater) is not set.
^ The HO2S voltage is greater than 0.351 volts but less than 0.473 volts.

ACTION TAKEN WHEN DTC SETS
The VCM turns on the Malfunction Indicator Lamp (MIL) after the second test failure.

CONDITIONS FOR CLEARING THE MIL/DTC
The VCM turns the MIL off after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

DIAGNOSTIC AIDS
Check the HO2S heater operation.

Never solder the HO2S wires. For proper wire and connector repairs, refer to Wiring Repairs.

TEST DESCRIPTION
The numbers below refer to the step numbers in the diagnostic table.

2. This step checks for other DTCs.
4. This step checks for physical damage to engine components and converter.