P0726
Symptom: CHECK GEARBOX lamp is on.
Engine speed, incorrect
Fault symptoms
CHECK GEARBOX lamp is on.
Conditions
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Engine speed greater than:
engine
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B2581
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B2341
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B2041
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rpm
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7500
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7200
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7200
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for longer than 10 sec.
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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
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Unplug the control module connector.
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Connect a test lamp to the connector between:
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Connect a diagnostic tool.
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Turn the ignition key to the ON position.
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Select “CURRENT ENGINE MANAGEMENT SYSTEM”.
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The lamp should flash.
Is the function OK?
Continue with step 3.
Continue with step 2.
2 Check the speed input lead
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Check the lead between the TCM pin 29 and
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motronic 5.2 control module, pin 80
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Motronic 4.1 control module, pin 47
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Trionic control module, pin 58
with respect to short/open circuits.
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Is the lead OK?
Continue fault diagnosis in the Service Manual for the relevant engine management system.
Rectify any faults. Continue with step 3.
3 Final check
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Clear the diagnostic trouble code
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Perform a driving cycle:
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Drive the car at varying loads and engine speeds for 5 min.
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Evaluate the driving cycle:
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Make sure the trouble code has not recurred.
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Has the trouble code recurred?
Continue with “Before changing a control module” in Service Manual 4:2 Automatic Transmission OBD II, M1996-.
The steps taken to rectify the fault were correct.
