MID 128, SID 57 Output, fuel pump (MPROP), fault

MID 128: Engine control unit Fault code

FMI 3:The voltage exceeds the normal value or is short circuited to higher voltage. FMI 9: Abnormal updating rate.

FMI Fault code explanation

3, 9 Faulty component / Faulty circuit

Fault indication

Warning is displayed in the tachometer/display. A red lamp flashes in the alarm display + audible warning.

Symptom

● Engine is difficult to start. ● Engine power is cut. ● If the MPROP supply cable is connected to battery voltage, the MPROP valve closes and the engine stops.

Connector (36 pin)

Circuit description

A magnetically controlled proportional valve (MPROP) controls the fuel pressure (rail pressure) to ensure that the correct fuel pressure is retained despite varying engine speed and loading. Signal from engine control unit (EDC7) is a PWM signal (pulse width modulated signal). When the current through the valve is changed, this affects the fuel flow, which results in changed fuel pressure. The rail pressure sensor senses the pressure and converts the pressure signal to a voltage which is registered by the engine control unit. The more the current to the valve solenoid rises, the less is the fuelpressure (rail pressure) obtained.

Fault tracing

FMI 3: Checking the circuit

Possible reason

If the MPROP supply cable is connected to 5 Volt, the MPROP valve opens somewhat, the fuel pressure is built up and lies somewhat above the nominal value.

Suitable action

Check cables and connections to the fuel pump (MPROP valve).

FMI 9: Checking the circuit

Possible reason

● Open circuit in MPROP battery negative cable. ● Open circuit in MPROP supply cable. ● Short circuit MPROP supply cable to battery negative. ● MPROP supply cable is short circuited to battery voltage. The MPROP valve closes and the engine stops.

Suitable action

Check cables and connections to the fuel pump (MPROP valve).

Measurements

Special tools: 9812519, 885675

1

NOTE! Cut the current with the main switch.

2

Remove the connector from the MPROP valve. Connect adapter cable 885675 to cable harness connector to engine control unit (EDC7).

3

Use multimeter 9812519 to do resistance measurement against the engine control unit. Note. Measurement is done to eliminate short circuiting or breaks in the cable to the engine control unit.

Measurement points Nominal value

1 – 2 R ≈ 60–86 kΩ 1 – Battery negative* R ≈ 60–86 kΩ 2 – Battery negative* R ≈ 0 Ω

*Note. Battery negative (–) on alternator or starter motor.

Checking the solenoid in the MPROP valve

Special tools: 9812519, 885675

1

NOTE! Cut the current with the main switch.

2

Remove the connector from the MPROP valve. Connect adapter cable 885675 to the valve.*

*NOTE! Do not not connect the other end of the adapter cable to the engine cable harness, since this can cause a measurement error.

3

Use multimeter 9812519 to check the resistance in the MPROP valve. Note. Measurement is done to eliminate short circuiting or breaks in the MPROP valve.

Measurement points Nominal value

1 – 2 R ≈ 2 – 3 Ω (at 20°C/68°F)

Checking the MPROP signal

Special tools: 9812519, 885675

1

NOTE! Turn the starter key to position 0.

2

Remove the connector from the MPROP valve. Connect adapter cable 885675 between the MPROP valve and the cable harness connector against the engine control unit (EDC7).

3

Connect multimeter 9812519 to measure the alternating current between the connections 1 and 2. Note. The MPROP signal is a PWM signal. An oscilloscope is needed for correct analysis of the signal.

4

NOTE! Turn the starter key to position I (driving position).

5

The multimeter should show that a voltage arrives at the MPROP valve.

Note. Measurement is done to eliminate short circuiting or breaks in the cable to the engine control unit. If there is an open or short circuit, the multimeter shows 0 Volt.