P0154

DIAGNOSTIC TROUBLE CODES P0151, P0152, P0154
Oxygen sensor 2 (front) cylinders 2-4-6, control module input, open circuit or shorting to ground/batt+.

Fault Symptom.
The CHECK ENGINE lamp (MIL) is on.

Conditions.
In the case of a short circuit or open circuit, a diagnostic trouble code will be generated on conditions that the engine is hot (coolant temperature 170°C [>158°F] for at least three minutes) and running under partial load.
Mass air flow sensor OK.

Diagnostic Procedure.

IMPORTANT: Contact cleaner or grease must not be used on the oxygen sensor connector.

1. Connect the Scan Tool.
Start the engine and warm it up to normal operating temperature.
Select "READ FUNCTIONS".
Select "FRONT OXYGEN SENSOR".
Check the oxygen sensor's voltage, which should oscillate between about 0.1 V and 0.9 V.
Vary engine rpm to obtain faster voltage variations.

If the measured value is correct, continue with step 5.
If the measured value is incorrect, continue with step 2.





2. Check the electrical interface for the oxygen sensor's preheater circuit.
Unplug the oxygen sensor's 4-pin connector.
Carry out the following checks:

^ Voltage measurement in the connector.
Engine idling.
Connect the test lamp across:
- pin 1 and battery negative
- pin 2 and battery positive
The test lamp should light up.

If it does not, continue with step 3.
If the test lamp lights up, the voltage levels in the preheater circuit are correct.

^ Resistance measurement.
Check the resistance of the oxygen sensor's preheater element by taking a reading across pins 1 and 2 of the oxygen sensor connector.
- The resistance should be 2.9 - 4 ohms.

NOTE: The resistance is temperature-dependent and will be higher the hotter the sensor is.
The sensor incorporates a current limiting PTC resistor.
At extremely high temperatures the resistance could go up to 10 ohms.

If the resistance is not OK, fit a new front oxygen sensor.
If the resistance is OK, continue with step 4.





3. The electrical connection of the preheater circuit is faulty.
No power supply or no ground connection.

If the test lamp does not light up when connected across pin 2 and battery positive, check the lead between pin 2 and grounding step G7P for continuity.
If the test lamp does not light up when connected across pin 1 and battery negative, no power supply will be obtained.

Power is supplied via fuse 28 and the fuel pump relay.
Since the engine starts (see step 1), the electrical circuit, fuel pump relay, fuse 14 and the fuel pump are all OK.
Check fuse 28.

If fuse 28 is intact and power is still absent, check the circuit between fuse 14 and pin I of the oxygen sensor connector for continuity.





4. Check the control module's electrical interface.
Ignition switch in the ON position.
Take a voltage reading across pin 4 and a good ground.
- A reading of 0.45 V should be obtained.
Check the operation of the control module and its wiring as far as the oxygen sensor.

If a reading of about 0 V is obtained, check the wiring between pin 4 of the oxygen sensor and pin 47 of the control module for continuity or a short circuit.
If the voltage reading is neither 0.45 V nor 0 V, check the lead between grounding step G7L and pin 10 of the control module for continuity.
If the voltage reading is about 0.45 V, fit a new oxygen sensor.

5. Clear the diagnostic trouble code and drive the car to see whether the DTC is generated again.

If the diagnostic trouble code is generated again, continue at "Procedure Before ECM Replacement". Component Tests
If the trouble code is not generated again the remedial measure taken was correct, otherwise the fault is of intermittent type.