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P0151,P0152, P0154

Symptom: CHECK ENGINE lamp (MIL) on

P0151 , P0152 , P0154

Oxygen sensor for cyl. 2-4-6 (front), input to control module low/high, absent, no continuity or shorting to ground/batt+


Fault symptom

CHECK ENGINE lamp (MIL) on

Condition

If, for a period of at least 2.5 seconds, the voltage at temperatures above 70°C (158°F) is

lower than 0.09 V, higher than 1.1 V or constant between 0.35 and 0.55 V.

Note

In the event of a break in the circuit, the control module will assume a value corresponding to a sensor voltage of 0.45 V.


Diagnostic procedure


1. Connect the ISAT, start the engine and run it at idling speed until it reaches normal operating temperature.

Use the ISAT command "OXY SENSOR 2-4-6" in the "READ FUNCTIONS" menu to check the voltage of the oxygen sensor, which should vary between 0.1 and 0.9 V. Vary engine rpm to obtain faster voltage variations.

If there is no voltage or if it does not vary with changing engine rpm, the fault probably lies with the oxygen sensor or a break in the signal lead between the sensor and the control module.

2. Unplug the front oxygen sensor's connector and take a reading on pin 1 of the signal lead connector to check whether the preheater element receives current from fuse 38.



Also check whether pin 2 is properly grounded at grounding point G7P.

Rectify any faults that may be present in the wiring.

3. Take a reading across pins 1 and 2 of the oxygen sensor connector to check the resistance of the sensor's preheating element.


The correct resistance is 2.9-4.0 ohms. Note that the resistance will be higher the warmer the sensor is, since the sensor contains a PTC resistor. (At extremely high temperatures the resistance may rise to 10 ohms.)

If the resistance is not correct, change the front oxygen sensor.

4. With the ignition switched off, connect a BOB to the MOTRONIC control module and cable.


Start the engine and measure the sensor voltage by taking a reading across pins 47 and 10 of the control module.

The voltage should normally vary between 0.1 and 0.9 V. In the event of no continuity in the sensor or wiring, the control module will utilize a fixed voltage of about 450 mV on pin 47.

Check the lead between pin 47 of the control module and pin 4 of the oxygen sensor connector for shorting to ground/batt+.

Note

If the voltage from the oxygen sensor is constantly high or constantly low, it may be because the fuel-air mixture is too rich or too lean (diagnostic trouble codes P0174 and P0175).

Check this before changing the oxygen sensor.


5. If no fault can be detected after carrying out the above checking procedure, clear the trouble code and drive the car on the road to check whether the trouble code is generated afresh. If it is, turn to for further diagnostic instructions.