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P0135

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

P0135

Heating, front heated oxygen sensor

Symptom of fault

The CHECK ENGINE lamp (MIL) is on.

Conditions




• Heating circuit active

• Heating circuit current below 500 mA or above 2300 mA for 5 seconds.


Diagnostic help

The oxygen sensor's heating circuit current can be ascertained using an ISAT scan tool.


- Select "READ FUNCTIONS".



- Select "PREHEAT OXY SENSOR FRONT"


With the engine hot, the ISAT scan tool should show a heating current of 700- 1000 mA. Heating of the oxygen sensors can be activated by means of the ISAT scan tool.


- Select "ACTIVATE".



- Select "OXY SENSOR FRONT".


If diagnostic trouble codes P0135 and P0141 are present, the cause of the fault is:

• because fuse 38 has blown

• in the lead between pin 8 of H33-4 and pin 87 of the pump relay

Checking the wiring. Intermittent faults may occur as a result of occasional short circuits and breaks in the wiring. Jiggle the leads and in-line connectors at several places and in different directions to reveal faults in the wiring harness. Observe the multimeter, ISAT scan tool or test lamp while carrying out this check.

Diagnostic procedure

1. Check additional diagnostic trouble codes in the Trionic system




- Obtain readouts of all diagnostic trouble codes using the ISAT scan tool.


Are P0135 and P0141 present?

yes

Continue with point 2.


no

Continue with point 3.


2. Check the oxygen sensors' heating circuit resistance


The engine should have been switched off for at least 5 minutes.


- Check fuse 38 and change it if necessary



- Unplug the 4-pin connectors of both oxygen sensors.



- Check the resistance of both sensors:

across pins 1-2 __________ar;_______ _ 1.8-4.0 ohms


Are the resistance readings OK?

yes

Repair or replace the leads between pin 1 of the connectors of both oxygen sensors and fuse 28. Then continue with point 4.


no

Change the relevant oxygen sensor and proceed to point 4.


3. Check the heating circuit ground connection and power supply



- Unplug the oxygen sensor's 4-pin connector.



- Start the engine and run it at idling speed.



- Connect the test lamp to:

• pin 1 and battery negative (B-)

• B+ and pin 2


Does the test lamp light up in both cases?

yes

Change the sensor and continue with point 4.


no

Rectify the lead in question and proceed to point 4.


4. Final check



- Clear the diagnostic trouble code.



- Implementation of driving cycle: Drive the car at varying engine rpm and loads for 5 minutes.



- Evaluation of driving cycle: Check whether the diagnostic trouble code has recurred.


Has the diagnostic trouble code recurred?

yes

Proceed to .


no

The remedial measure taken was correct.