Author Topic: Tachometer (RPM) not working and ESP OFF light on.  (Read 667 times)

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Tachometer (RPM) not working and ESP OFF light on.
« December 19, 2018, 04:28:37 »
Tachometer not working and ESP OFF light on.

This is a complaint that reoccurs online, but, as yet has not been conclusively resolved. Unfortunately, original posters seeking advice, rarely have the courtesy to advise their advisors of the failings or the success of proposed remedies.
 Drilling down into the inter-babble, I conclude that the probable cause is a failing crank shaft position sensor (CKP).

A crank sensor (CKP) is an electronic device used in both petrol and diesel engines to monitor the position or rotational speed (RPM) of the crankshaft. This information is used by engine management systems to control the fuel injection, the ignition timing and other engine parameters.

Usually the complaint involves: Occasional hard engine start, ESP OFF light is displayed then clears when car is started, Rev Counter remains on 0 RPM when driving, the car has slightly lower power or acceleration than expected.
MIL : The codes for CKP faults are P0335 to P0339 , but they are rarely present.

In a recent case, erroneous fault codes were displayed:
B1102 - Restraints
B2500 - Air bag
C1260 - Brake ABS/ESP
C1260 - Steering Angle Sensor Circuit-Signal
C1611 - Steering Electronic Power
C1623 - Steering Angle Sensor
In this case, mechanics incorrectly concluded that the steering sensor was at fault. They failed to include the tacho failure in their assumption.

Here, the intermittent Tacho failure is crucial.
None of the codes directly indicate loss of RPM signal. But, all the named functions, including restraints and air bags, require knowledge of the vehicle's speed (RPM) to operate correctly; therefore, they submit a fail code when the data is not consistent.
 
Conclusion:
 If the CKP fails there is a loss of RPM data flowing to the ECU/ECM. However, it appears that in many cases, the ECU will be able to function in a sub-optimal mode to control fuel injection and ignition system timing parameters. In other words, the car keeps running, albeit slower and probably unreliably! But, the crank sensor is the culprit.
 


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