P0136,P0137, P0138, P0139,P0140

/ 900 / 1997 / 2. Engine / Motronic 4.1 OBD II / Fault diagnosis, diagnostic trouble codes / P0136,P0137, P0138, P0139,P0140

Symptom: CHECK ENGINE lamp (MIL) on. Any other diagnostic trouble codes, such as misfiring and adaptation.

P0136 , P0137 , P0138 , P0139 , P0140

Rear heated oxygen sensor (oxygen sensor 2)

Fault symptoms

CHECK ENGINE lamp (MIL) on. Any other diagnostic trouble codes, such as misfiring and adaptation.

Conditions

Sensor preheating active more than 200 seconds after starting

and

P0136 Sensor 2 voltage = 0 V for 200 seconds.

P0137 Shorting to ground for more than 0.12 seconds,

P0138 Shorting to battery positive (B+) for more than 0.12 seconds.

P0139 Sensor 1 voltage oscillates at too low a frequency.

P0140 No voltage from the sensor, open circuit for more than 100 seconds.

Diagnostic help

The performance of the oxygen sensor can be ascertained with an ISAT scan tool.

Select "READ FUNCTIONS".

Select "OXYGEN SENSOR".

Read "OXYGEN SENSOR 2"

At full load the ISAT scan tool should show a reading that is > 0.7 V. At fuel shut-off the ISAT scan tool should show a reading of about 0 V.

Note

•

If the reference ground or sensor voltage of any of the oxygen sensors is shorted to battery negative (B-), diagnostic trouble codes P0131 and P0137 could be generated simultaneously.

•

If the reference ground or sensor voltage of any of the oxygen sensors is shorted to battery positive (B+), diagnostic trouble codes P0131 and P0138 could be generated simultaneously.

•

If battery positive voltage (B+) is applied to any reference ground, the control module could be damaged.

If the preheating element of an oxygen sensor develops a fault the performance of the sensor will deteriorate, particularly at idling speed. A diagnostic trouble code indicating a defective sensor could then be generated. If a diagnostic trouble code for oxygen sensor preheating is generated, it should be attended to first. Following this, the performance of the oxygen sensor should be checked.

Check the wiring

Intermittent faults may occur as a result of temporary short circuits and breaks in the wiring. Jiggle the wiring at several points and in different directions to ascertain whether the wiring harness, including any connectors, is causing the trouble. Observe the multimeter, ISAT scan tool or test lamp while doing this.

Diagnostic procedure

1. Check other Motronic 4.1 diagnostic trouble codes

Use an ISAT scan tool to obtain readouts of all diagnostic trouble codes.

Any other diagnostic trouble codes?

yes

Continue fault diagnosis for the relevant diagnostic trouble code.

Continue with point 2.

2. Check the oxygen sensor's control module input

Unplug the oxygen sensor's 4-pin connector.

Connect the ISAT Scan Tool.

Turn the ignition switch to the ON position.

Select "READ FUNCTIONS".

Select "OXYGEN SENSOR".

Read "OXYGEN SENSOR 2"

The ISAT scan tool should show a reading of about 0.45 V.

Connect a jumper lead between pins 3 and 4 in the oxygen sensor's connector.

The ISAT scan tool should show a reading of 0 V.

Are all readings OK?

yes

Change the oxygen sensor. Continue with point 4.

Check the relevant lead and repair or replace it if necessary. Continue with point 3.

3. Check the wiring

Check for continuity between:

If the ISAT scan tool shows the two diagnostic trouble codes P0137 and P0131, the front heated oxygen sensor's ground connection should also be checked.

Check for continuity between:

Is the wiring OK?

yes

Continue with point 4.

Repair or replace the wiring. Continue with point 4.

4. Final check

Clear the diagnostic trouble code.

Implementation of driving cycle:

Evaluation of driving cycle:

Does the ISAT scan tool read "NOT READY"?

yes

Repeat the driving cycle.

Check whether the diagnostic trouble code has recurred.

Has the diagnostic trouble code recurred?

yes

Continue as described in .

The steps taken to rectify the fault were correct.