I have been asked this question a couple of times now, “the car is Drive-By-Wire how do we get a TPS signal and why is it that you are using Pin 31 of the MS45 DME rather then Pin 32?”.

Well all DBW systems use 2 potentiometers for safety, this is so we have no mistakes in calculations and the throttle opens too much for too long (remember the Toyota issue?).

The EDK (electronic throttle Valve) has 2 voltage signals, 5-0V and 0-5V. Pin 32 is 5-0V while Pin 31 is 0-5V and more common as most TPS ranges are from 0-5V. So we want to use either Pin 19 (MS43) or Pin 31 (MS45) for the TPS signal to use for TPS load if you are going to stay N.A. Set the Unichip so it scales from a min. of .5 volts and a max. of 4.5 Volts in the TPS Map set up.

tpsmapsetup

Here it how it works based on the WDS:

The corresponding position of the throttle valve is calculated in the engine control unit from the position of the accelerator pedal and other variables. The throttle valve is opened and closed electrically by the engine control unit.

Function

Two potentiometers register the current position of the throttle valve. The engine management controls the position by means of the electric drive until the current valve opening corresponds to the set position. Two potentiometers are used for safety reasons. The characteristic curves of the two potentiometers are contra-rotating. The engine control unit powers both potentiometers with an exact voltage of 5 V. This voltage source is also used to supply sensor 1 of the pedal position sensor or accelerator pedal module.

Throttle-valve potentiometer characteristics

  • Sensor angle
  • Output voltage
  • Signal path of throttle-valve potentiometer 1
  • Signal path of throttle-valve potentiometer 2

Monitoring the signal voltages

The engine control unit permanently monitors the two voltages of the potentiometers. The monitoring function checks whether the two signal voltages are within the permissible range and are plausible in relation to one another. It also monitors whether there is a short circuit. The engine control unit can determine which of the two signal voltages is faultless based on the air mass signal.

If the engine control unit detects that the signal voltage of a potentiometer is defective, the maximum possible valve opening is limited to 20 degrees.

If the signal voltages of both potentiometers are detected as implausible, the activation of the throttle valve is switched off. Under these circumstances, it is no longer possible to determine the current position of the throttle valve and, consequently, the return spring closes the throttle valve.

Monitoring the throttle valve position

The engine control unit continuously checks whether the actual position corresponds to the set position of the throttle valve. thus making it possible to determine when a valve is sticking. In the case of fault, for safety reasons, the maximum possible engine speed is limited to 1300 rpm.

A stiff throttle valve that therefore moves only slowly is switched off and closed by the return spring. In this case, the maximum possible engine speed is limited to 1300 rpm by cutting out the fuel injection.

Pin outs between the Throttle and DME.

Abbreviations used in this circuit from BMW:

MDK – Motorized Throttle Valve/System

MDK1 – Activate motor Throttle position actuator

MDK2 – Activate motor Throttle position actuator

EDK – Electronic Throttle Valve

DKG – Throttle Position Potentiometer

DKG1 – Throttle position signal 1 (Pot 1) Electrical gas actuator

DKG2 – Throttle position signal 2 (Pot 2) Electrical gas actuator

DKP – Throttle Angle, throttle plate position