P0131

DIAGNOSTIC TROUBLE CODES P0131, P0132 and P0134
Oxygen sensor, input to control module low/high,
No continuity, absent, or shorting to ground/batt+.

Fault Symptom.
CHECK ENGINE lamp (MIL) on.

Condition
Voltage lower than 0.04 V for at least 25 seconds when engine temperature is above 70°C (158°F), or
Voltage higher than 1.1 V for at least one second when engine temperature is above 70°C (158°F), or
Voltage stationary between 0.40 and 0.55 V for at least one second when engine temperature is above 70°C (158°F).

NOTE: If the oxygen sensor is faulty, the control module utilizes a fixed signal voltage of 0.5 V.

Diagnostic Procedure.
To begin with, check that the 0-ring fitted to the resonator (silencer) where it connects to the throttle body is in good condition and that no air leakage occurs.
1. Connect the ISAT, start the engine and run it at idling speed until it reaches normal operating temperature.
Use the ISAT command "OXYGEN SENSOR" in the "OBTAIN READOUTS" menu to check the voltage of the oxygen sensor, which should normally 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 oxygen sensor connector and, with the engine running at idling speed, take a reading on pin 1 of the connector to check whether the preheater element receives current from fuse 17.
Also check whether pin 2 is properly grounded at grounding step 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 (12 W variant) or 1.8-2.5 ohms (18 W variant).
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 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 28 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 0.5 V on pin 28.
Check the lead between pin 28 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 P0171 and P0172). 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, continue at "Before Control Module Replacement" for further diagnostic instructions. Before Replacing A Control Module