General
The control unit electronics run a self-test commencing as soon as terminal 15 is activated; thereafter, system monitoring is continuous. Errors are stored in the non-volatile error memory.
The operating parameters and the fault memory contents are read by the tester via the diagnosis interface. Furthermore, in this way, it is possible to check the activation of actuators.
Special functions such as matching are available under the “service functions” menu.
The following points are discussed in greater detail in this chapter:
– Diagnosis of injectors – DDE 4.0 M57
– Diagnosis of rail pressure control valve – DDE 4.0 M57
– Diagnosis of rail pressure sensor – DDE 4.0 M57
– Diagnosis of pre-supply pressure sensor – DDE 4.0 M57
– Diagnosis of Hall sensor for camshaft – DDE 4.0 M57
– Monitoring of pre-supply pressure – DDE 4.0 M57
– Monitoring of rail pressure – DDE 4.0 M57
– Service functions – DDE 4.0 M57
– Checking and adjusting injectors
– Measuring engine smoothness
Injector diagnosis (DDE 4.0 M57)
The injectors are under the pressure of the fuel in the rail at all times. It is only when the injectors are electrically actuated by the DDE control unit that they open to inject fuel into the combustion chambers.
Fault monitoring
The electrical lines leading to the fuel injectors and the coils in the injectors are monitored for shorts and breaks. Monitoring also includes the current in the control unit. If a defect occurs an error is registered in memory for the injector in question, in accordance with the following list:
– 0200: cylinder No. 1 injector
– 0201: cylinder No. 2 injector
– 0202: cylinder No. 3 injector
– 0203: cylinder No. 4 injector
– 0204: cylinder No. 5 injector
– 0205: cylinder No. 6 injector
The voltage transient in the injector output stages is monitored in the electronic control unit; if a defect occurs a fault is registered in memory as follows:
– 1E45: capacitor voltage 1 for cylinders 1, 2, 3
– 1E50: capacitor voltage 2 for cylinders 4, 5, 6
Caution: If an injector fault occurs with the fault type “current on high side too high” or “current on low side too high”, although the fault is assigned to a fuel injector, the cause of the fault may be due to the combined lines (U_MV1 and U_MV2 for one bank) in any of the leads of the three cylinders of the bank concerned.
Reactions to faults
If a fuel injector fault occurs with the fault type “current on high side too high” or “current on low side too high”, the engine shuts down, with fault type “load drop” (line break) the engine continues to operate if no more than one injector is affected.
A fault in the output stages results in engine shutdown.
Rail pressure control valve diagnosis (DDE 4.0 M57)
The rail pressure control valve is an electrically actuated solenoid valve mounted on the high pressure pump. The DDE actuates the rail pressure control valve with a computed sampling ratio in order to ensure that the pressure of the fuel in the rail settles to the setpoint calculated by the DDE. Depending on the activation, the rail pressure control valve allows more or less fuel to flow from the high pressure side into the depressurized return valve thus controlling the required pressure on the high pressure side.
Fault monitoring
The electric wires to the rail pressure control valve are monitored for short-circuit and open-circuit, as is the valve’s coil. If a fault occurs at these points, fault code 1195 “rail pressure control valve” is stored.
Reactions to faults
If the rail pressure control valve is faulty it is activated with the minimum pulse-duty factor and the injection quantity is limited.
Rail pressure sensor diagnosis (DDE 4.0 M57)
The rail pressure sensor registers the fuel pressure in the rail; it acts as measured-value transducer, generating the signal for injection-rate metering and rail-pressure control.
The rail pressure sensor is mounted at the rear end of the rail.
The DDE control unit supplies the sensor’s ground (M_KDF) and a 5 V supply voltage (U_KDF).
The sensor registers the pressure and sends the corresponding voltage signal (A_KDF) to the DDE control unit.
Fault monitoring
The electrical lines to the rail pressure sensor as well as the supply voltage in the control unit are monitored for shorts and breaks. If a fault occurs, fault code 0190 “rail pressure sensor” is stored.
Reactions to faults
If a fault occurs at the rail pressure sensor, a substitute value is output and the injection volume limited.
Diagnosis of pre supply sensor (DDE 4.0 M57)
The pre-supply pressure sensor registers the absolute pressure (sum of pre-supply pressure and atmospheric pressure) in the fuel delivery line after the fuel filter; its purpose is to monitor the fuel supply.
The pre-supply pressure sensor is integrated into the fuel filter housing. The DDE control unit supplies the ground (M_KND) and a 5 V supply voltage (U_KND) for the sensor; the sensor returns a voltage signal (EA_KND) to the DDE control unit.
Fault monitoring
The electrical lines to the prepressure sensor as well as the supply voltage in the control unit are monitored for shorts and breaks. If a fault occurs, fault code 1255 “pre supply sensor” is stored.
Reactions to faults
If the pre-supply pressure sensor is faulty a dummy value is output by the DDE.
Diagnosis of camshaft Hall-effect sensor (DDE 4.0 M57)
The Hall sensor for the camshaft is mounted at the front end of the cylinder head. The camshaft has a rectangular protrusion at the front; this protrusion passes the Hall sensor as the camshaft rotates. The DDE control unit evaluates the resulting voltage signal (one square-wave signal per camshaft revolution). This signal is used for synchronisation
With the aid of the camshaft signal, when the engine is started, the DDE control unit recognises whether there is an injection or gas change TDC and can thus activate the correct injector for fuel injection.
It is not possible to start the engine without synchronisation!
Fault monitoring
Fault code 1E25 “rpm sensor monitoring” is stored if a faulty signal is recognised. A faulty camshaft signal can be due to two types of fault:
– Camshaft signal frequency too high
– Failure of camshaft signal
Caution: There are two other modes for this fault code and both are indicative of a faulty crankshaft signal:
– Failure of crankshaft signal
– Crankshaft signal dynamically implausible
Reactions to faults
Failure while engine is running: No effect, except that boost pressure control is deactivated and once switched off, the engine will refuse to restart if the fault persists.
Monitoring pre supply pressure (DDE 4.0 M57)
During the engine start phase, the pre-supply pressure is monitored by the pre-supply pressure sensor integrated in the fuel filter housing; while the engine is running this pressure is monitored by a nominal/actual-value comparison (see flowchart below).
Note: The engine remains operational if the in-tank pump fails, but not if the in-line pump fails.
Fault monitoring
If the DDE determines an impermissible deviation in the pre-supply pressure from the setpoint, fault code 1260
“pre-supply pressure monitoring” is stored.
Note: Alongside the pre-supply pressure, the pressure in the fuel return line is of vital importance as regards correct
fuel injection. The pressure in the fuel return line must not exceed 1.5 bar (absolute), as otherwise the supply/return
pressure differential across the high pressure pump as required for correct priming of the fuel rail is imbalanced. The DDE does not register the pressure in the fuel return line.
Reactions to faults
Depending on the extent of the deviation, the injection quantity is reduced or the engine is shut down or engine start is disabled.
Rail pressure monitoring (DDE 4.0 M57)
The actual value for rail pressure monitoring is supplied by the rail pressure sensor; the setpoint is calculated by the DDE as a function of the operating status.
Fault monitoring
Requirements for monitoring:
– Engine speed > 550 rpm
– Rail pressure control in operation
– No fault registered for the rail pressure sensor
The following rail pressure control variables are monitored by the DDE:
– Rail pressure inside minimum and maximum limits
– Manipulated variable at rail pressure control valve inside minimum and maximum limits
– Plausibility of rail pressure and manipulated variable
If the DDE determines an impermissible deviation, fault code 1190 “rail pressure plausibility” is stored.
Reactions to faults
Fault 1190 results in engine shutdown.
Possible causes of the fault:
– Fuel tank empty
– Faults in pre-supply system
– Internal or external leaks in the high pressure system
– Efficiency of the high pressure pump inadequate
– Injector leak-off rate excessive
– Control quantity for injectors too high
– Rail pressure control valve sticking
Service functions (DDE 4.0 M57)
The service functions provided for DDE 4.0 by diagnosis are as follows:
– Comparison/adjustment of idle speed
– Comparison/adjustment of exhaust-gas recirculation
– Comparison/adjustment of limitation quantity
– Comparison/adjustment of starting fuel delivery
– Comparison/adjustment the injectors
– Comparison/adjustment of DDE-EWSIII
– Measuring engine smoothness
The new functions not implemented for DDE 3.0 are calibration of injectors and measurement of engine smoothness.
Matching fuel injectors
By way of compensating for tolerances in the fuel injection system, a characteristic map with engine-specific compensation values is programmed into the electronic control unit at the end of the assembly line. If one or more injectors are replaced (and only then), the calibration values must be set to 0 as part of the matching procedure. Calibration can be used only for this purpose, in other words for setting these values to 0.
Comparing/adjusting of injectors: implementation
Calibration can be included in the test plan by means of:
– Service functions
– Digital Diesel Electronics
– Calibrating the injectors
Once calibration is started, the procedure for setting the compensation values to 0 is as follows:
1. select 1 “reset calibration values to 0”
2. “end with programming”.