P0154

Circuit Description

The PCM supplies a bias voltage of about 450 mV between the HO2S signal and low circuits. When measured with a 10 megohm digital voltmeter, this may display as low as 320 mV. The oxygen sensor varies the voltage within a range of about 1000 mV when the exhaust is rich, down through about 10 mV when exhaust is lean. The PCM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary. If the Bank 2 HO2S 1 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0154 will be set, indicating an open sensor signal or sensor low circuit.

Conditions for Running the DTC

^ No Misfire, CKP, Fuel Injector, MAF, TP, EVAP, IAT, MAP, Fuel Trim, EGR or ECT DTCs are set.
^ System voltage is greater than 9 volts.
^ The engine must be running for at least 4 minutes.

Conditions for Setting the DTC

Bank 2 HO2S 1 signal voltage remains between 400 mV and 500 mV for longer than 2.5 minutes.

Action Taken When the DTC Sets

^ The PCM will illuminate the MIL during the second consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.

Conditions for Clearing the MIL/DTC

^ The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.
^ The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using the Scan Tool.

Diagnostic Aids

Check for the following conditions:

^ Poor connection at the PCM - Inspect 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 - Inspect the wiring harness for damage.
^ Faulty HO2S heater or heater circuit - With the ignition ON the HO2S voltage displayed on a scan tool should gradually drop to below 300 mV or rise to above 600 mV. If not, disconnect the HO2S and connect a test lamp between the HO2S ignition feed and heater ground circuits. If the test light does not light, repair the open ignition feed or sensor ground circuit as necessary. Refer to Wiring Repairs in Diagrams. If the test light lights and the HO2S signal and low circuits are OK, replace the HO2S.
^ Intermittent test - With the ignition ON, monitor the HO2S signal voltage while moving the wiring harness and related connectors. If the fault is induced, the HO2S signal voltage will change. This may help isolate the location of the malfunction.

Test Description

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

3. If the DTC P0154 test passes while the Fail Records conditions are being duplicated, an intermittent condition is indicated. Reviewing the Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.
12. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.