W54.00-0040-01
General notes on plausibility check:
The coolant and fuel temperature sensors of the MR (PLD) have the same curve. Depending on the ambient or engine temperature the valid value can be between 300 Ω or 25 kΩ. The limit values (approx. 300 Ω at 80°C and approx. 10 kΩ at -10°C) of the boost pressure sensor are similar.
The monitoring circuit in the control module only recognizes a sensor defect if the sensor limit values are not reached or are exceeded (short-circuit or open-circuit).
If a sensor limit value is not reached or is exceeded the control module
regulates the engine with a substitute value optimized for all engine operating conditions,
stores a corresponding fault code in the memory
and
displays the fault in the display of the large instrument or instrument.
The substitute value is displayed as a valid actual value when the measured values are retrieved.
A defective sensor, e.g. which is in the valid range with a fixed resistance value between the lower and upper limit value, cannot be recognized by the control module as defective.
In this case a sensor defect does not trigger either the use of an optimized substitute value or the display of a fault code in the control module.
Unusual operating conditions such as
lack of performance
increased fuel consumption
increased black smoke
white smoke when starting,
or
problems with starting the engine
can indicate a sensor defect not recognized by the control module.
When unusual engine operating conditions occur without a fault code being displayed, a plausibility check of the corresponding sensors should always precede troubleshooting on the mechanical components of the engine.
The plausibility check should preferably be carried out on a cold engine. A check on a hot engine which has been switched off is also possible and in cases of doubt can improve fault detection in connection with the check on a cold engine.
The displayed temperature values of the temperature sensors should be roughly the same when the engine is cold and hot.
The permissible deviation of the temperature values is:
5°C on a cold engine
and
20°C on a hot engine.
Plausibility check:
1 Press the "SYSTEM" button with ignition switched on until the system code designation of the control module required appears on the display.
2 Call up the measured values (MW) of temperature sensors on the display by pressing the "INFO" button.
3 Compare displayed measured values with each other.
Sample display on a cold engine:
Measured value 13 MR/PLD MW 13
Engine coolant temperature sensor + 23
Measured value 14 MR/PLD MW 14
Fuel temperature sensor + 42
Measured value 16 MR/PLD MW 16
Engine oil temperature sensor + 24
Measured value 17 MR/PLD MW 17
Charge air temperature sensor + 21
In the sample display the measured value 14 (MW 14) of the fuel temperature sensor deviates considerably from the comparable measured values of the other sensors. The temperature value deviation indicates a sensor defect or a fault in the sensor circuit.