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P0726

Symptom: CHECK GEARBOX lamp is on.

P0726

Engine speed, incorrect




Fault symptoms

CHECK GEARBOX lamp is on.

Conditions




Engine speed greater than:

engine
B2581

B2341

B2041

rpm
7500

7200

7200



for longer than 10 sec.


Check the wiring

Intermittent faults may arise due to temporary short circuits or open circuits. Jiggle the wiring harness in several places and in varying directions to reveal any problems in the wiring harness or connectors. Observe the multimeter, Tech 2 or test lamp during the check.


Diagnostic procedure

1 Check the output signal from the engine management system



- Unplug the control module connector.

- Connect a test lamp to the connector between:

pin 18 and pin 29.

- Connect a diagnostic tool.

- Turn the ignition key to the ON position.

- Select “CURRENT ENGINE MANAGEMENT SYSTEM”.

- Activate “ENGINE RPM”.


The lamp should flash.

Is the function OK?

YES

Continue with step 3.


NO

Continue with step 2.


2 Check the speed input lead



- Check the lead between the TCM pin 29 and

motronic 5.2 control module, pin 80

Motronic 4.1 control module, pin 47

Trionic control module, pin 58

with respect to short/open circuits.


Is the lead OK?

yes

Continue fault diagnosis in the Service Manual for the relevant engine management system.


no

Rectify any faults. Continue with step 3.


3 Final check


- Clear the diagnostic trouble code

- Perform a driving cycle:

Drive the car at varying loads and engine speeds for 5 min.

- Evaluate the driving cycle:

Make sure the trouble code has not recurred.


Has the trouble code recurred?

YES

Continue with “Before changing a control module” in Service Manual 4:2 Automatic Transmission OBD II, M1996-.


NO

The steps taken to rectify the fault were correct.