MAN Truck Edc Troubleshooting Manual

MAN Truck Edc Troubleshooting Manual
MAN Truck Edc Troubleshooting

These instructions are intended to help you properly carry out repairs on the electronically controlled diesel injection system described in this document. In writing these instructions, we have assumed that you have the necessary knowledge of control systems for working on and with the electronic diesel control.

The idle speed control operates in the same way as the intermediate engine speed control. The idle speed is exactly maintained by means of the idle speed governor as long as the engine output is sufficient for this. The regulated idle speed can be varied within certain limits. Starting-fuel delivery is output when either a lower start recognition speed is exceeded. The starting fuel volume and cold idle speed are limited as a function of the coolant temperature to avoid impermissible smoke emission and unnecessary revving of the engine after starting.

Electromagnetic fuel-delivery regulator Description:
The fuel-delivery regulator operates in conjunction with the P-pump. The most important component of the fuel-delivery regulator is a linear solenoid whose armature acts directly on the control rod thus determining the injection volume by means of the control position. When no power is applied, the control rod is held in the stop position by means of a spring.

Resistor bank
On commercial vehicles, certain items of data are fed to the EDC which are not required for railway operation. An example of such data is a signal from the tachograph (speedometer, tachograph) which is used for controlling or limiting the driving speed (see Page 36). Some unused EDC connections must be closed by resistors since the EDC constantly conducts a signal range check, as described on Page 21.

Electrohydraulic shut-off device EHAB
The EHAB (electrohydraulic shut-off device) is a safety-relevant component. The EHAB shuts off the fuel supply to the injection pump in the event of certain faults occurring in the EDC system. The EHAB is connected into the fuel supply system between the delivery pump and pump suction chamber. The EHAB reverses the delivery direction of the delivery pump so that the pressure in the suction chamber is reduced rapidly thus interrupting the filling procedure.

Power is always applied to the EHAB during operation. The power circuit is interrupted by the EDC control unit in order to activate the EHAB (e.g. for emergency engine shut-down). For this reason, the ignition must be turned on when bleeding the fuel system by means of the presupply pump.

The EDC system continuously checks itself by means of a signal-range check. It does this by running a signal-range check. During this check, all signals are scanned for presence and plausibility within a certain time frame (determined by the software). The control unit itself is also constantly checked the whole time the program is running. The first check is always carried out when the ignition is turned on. Any faults occurring during operation are stored for the purpose of subsequent diagnosis. A maximum of 5 faults can be stored simultaneously in the fault memory. The faults are stored in the order in which they occurred. If more than 5 faults occur, the least significant fault is deleted.

Fault storage includes

  1. allocation of fault priority,
  2. identification of the type of fault,
  3. recording of fault frequency.

Sporadic faults are recorded by a frequency counter the first time they occur. This means that a certain frequency number is set which is decremented by one during every start procedure. If the fault no longer occurs, it is deleted when the counter reaches zero. To report the fault, the diagnostic lamp either comes on permanently or remains off, depending on the significance of the fault. If several faults are stored, the steady light has priority over OFF. Only faults currently present are indicated. Faults which are stored but which are not currently present are not indicated.