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98 STS P0154 CODE

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O2 sensor bank 2, sensor 1. So this is the O2 sensor mounted on the front side exhaust manifold.

The PCM provides a 0.45 volt reference to the oxygen sensor on CKT 412. 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 front heated oxygen sensor is located in the manifold before 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 P0154. Possible causes of DTC P0154 are:

Open in CKT 412 or 413.

Short to voltage on CKT 412 or 413.

Oxygen sensor that malfunctions.

An ineffective oxygen sensor heater.

A poor HO2S ground.

Conditions for Running the DTC

DTCs P0117, P0118, P0121, P0122 and P0123 not set.

Coolant temperature 72.5°C (163°F) or greater.

Throttle between 1 and 81.6 degrees.

(Calculated) Throttle position switch open.

Engine speed 800 RPM or greater.

Conditions for Setting the DTC

Oxygen sensor voltage stays between 0.302 volt and 0.600 volt for 50 out of 64 seconds (oxygen sensor voltage not toggling).

Action Taken When the DTC Sets

PCM enables Evaporative Emission (EVAP) control solenoid if DTC P0131, P0132, or P0134 is also set.

Closed Loop and long term fuel trim operation disabled if DTC P0131, P0132, or P0134 is also set.

PCM uses rear oxygen sensor feedback for Closed Loop and long term fuel trim operation if DTCs P0131, P0132 and P0134 are not set.

The PCM will illuminate the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.

Conditions for Clearing the MIL/DTC

The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.

A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.

A History DTC will clear after forty consecutive warm-up cycles with no failures of any emission related diagnostic test.

Use a scan tool to clear DTCs.

Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation.

Diagnostic Aids

Use the scan tool snapshot and graph function to aid in diagnosing sensor performance failures. Refer to scan tool users guide for further information.


Do not solder heated oxygen sensor wires. Soldering the wires will result in the loss of the air reference to the sensor. Refer to Engine Electrical for proper wire and connection repair techniques.

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.

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