P0154

CIRCUIT DESCRIPTION
The VCM supplies a voltage of about 0.45 volt between the HO2S High and the HO2S Low circuits. (If measured with a 10 megohm digital voltmeter, this may read as low as 0.3 volt.) The Heated Oxygen Sensor (HO2S Bank 2, Sensor 1) varies the voltage within a range of about 1.0 volt if the exhaust is rich, down through about 0.1 volt if the exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below 360°C (600°F).

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 P0154 determines if the HO2S or the HO2S circuit has developed an open. The DTCs P0154 is a type A 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 DTCs.
^ No ECT sensor DTCs.
^ No MAF DTCs.
^ No EGR DTCs.
^ No intrusive test in progress.
^ No device controls active.
^ System Voltage is at least 9 volts The engine run time is at least 2 minutes.

Open Test Enable

^ The engine run time is at least 2 minutes.
^ DTC P0151 is not active.
^ A Closed Loop.
^ The HO2S (Bank 2, Sensor 1) voltage is greater than 299 mV but less than 598 mV.

ACTION TAKEN WHEN DTC SETS
With a current DTC set, 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
A poor connection, rubbed through wire insulation, or a wire broken inside the insulation may cause an intermittent.

Check for the following:

^ A poor connection or a damaged harness Inspect the harness connectors for the following conditions:

- Backed out terminals
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Poor terminal to wire connection
- Damaged harness.

^ A faulty HO2S (Bank 2, Sensor 1) heater or heater circuit.

1. With the ignition ON and the engine off, the HO2S (Bank 2, Sensor 1) voltage displayed on a scan tool should gradually drop to below 0.300 volt, indicating that the heater is working properly.
2. If not, disconnect the HO2S (Bank 2, Sensor 1) and connect a test lamp between the terminals C and D.

^ If the test light does not light, repair the open in the affected circuit.
^ If the test light lights, replace the HO2S (Bank 2, Sensor 1).

^ An intermittent test: With a scan tool, monitor HO2S (Bank 2, Sensor 1) signal voltage while moving the related connectors and wiring harness, with a warm engine running at part throttle in a Closed Loop. If the failure is induced, the HO2S (Bank 2, Sensor 1) signal voltage reading will change from its normal fluctuating voltage (above 600 mV and below 300 mV) to a fixed value around 450 mV. This may help to isolate the location of the malfunction.

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

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

2. If the conditions for setting DTC P0154 exist, the system will not go into a Closed Loop.
3. This step will determine if the sensor or the wiring is the cause of DTC P0154.