MID 128, PID 97 Water switch, fuel filter

MID 128: Engine control unit Fault code

FMI 0:The value is valid but exceeds the normal working range. FMI 9: Abnormal updating rate.

FMI Fault code explanation

0 Water in fuel 9 Faulty sensor / Faulty sensor circuit

Fault indication

Warning is displayed in the tachometer/display. FMI 0:Indication for “water in fuel” flashes in the alarm display. FMI 9:An orange lamp flashes in the alarm display.

Symptom

Engine stops when there is a short circuit in the monitor power supply cables.

Connector (36 pin)

Circuit description

The monitor consists of a measurement probe containing two measurement points, galvanically isolated by a layer of insulation. The measurement probe is in contact with the fuel. When there is no water in the fuel, the resistance between the measurement points is very high. If there is any water in the fuel, the resistance falls. At a threshold resistance (water has been detected), the monitor (pin 1) will give an output signal which is proportional to the monitor supply voltage. Pin 16 on the engine control unit (EDC7) provides pin 2 on the monitor with battery voltage. Pin 3 on the monitor is connected to battery negative via pin 3 on the engine control unit.

Fault tracing

FMI 0: Water in fuel

Possible reason

● Water in the fuel filter. ● Short circuited monitor signal cable to battery voltage or 5Volt voltage. ● Fault in sensor. ● Intermittent contact in the power supply or negative cable to the sensor. The fault code is shown as being inactive.

Suitable action 1

Empty the water tap under the fuel filter or secondary fuel filter.

2

Empty the fuel tank sludge trap.

3

If there is an inactive fault code: Check the monitor power supply and negative cables.

4

Check the monitor.

FMI 9: Checking the monitor

Conditions for fault code

Abnormal updating rate.

Possible reason

● Open circuit in monitor signal cable (engine control unit (EDC7) sets a fault code when the ignition is turned on, not if a fault occurs during operation). ● Open circuit in monitor negative cable (engine control unit sets a fault code when the ignition is turned on, not if a fault occurs during operation). ● Open circuit in monitor power supply cable (engine control unit sets a fault code when the ignition is turned on, not if a fault occurs during operation). ● Open circuit, all cables failed (engine control unit sets a fault code when the ignition is turned on, not if a fault occurs during operation). ● Short circuited monitor signal cable to battery negative. ● Short circuited monitor power supply cable to battery negative. ● Faulty monitor.

Suitable action 1

Check the cables and the connectors between the monitor and the engine control unit (EDC7).

2

Check the monitor.

Measurements

Special tools: 9812519

Negative cable

1

NOTE! Cut the current with the main switch.

2

Remove the connector from the monitor.

3

Use multimeter 9812519 to do resistance measurement against the engine control unit (EDC7).

Supply cable

1

Remove the connector from the monitor.

2

Turn the main switches on. Turn the starter key to position I (driving position).

3

Use multimeter 9812519 for voltage measurement.

Measurement points Nominal value

2 – 3 U ≈ Battery voltage

Measurement points Nominal value

3 – Battery negative* R ≈ 0 Ω

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

Checking the water monitor, fuel filter

Special tools: 885675, 9812519

1

Undo the connector and remove the water sensor from the secondary fuel filter.

2

Connect the monitor to adapter cable 885675.

3

Connect a +12 V alt. +24 V power supply to measurement connection 2 on the adapter cable. Connect measurement connection 3 to the power supply battery negative terminal.

4

Use multimeter 9812519 to measure the voltage between measurement connection 1 and measurement connection 3 on the adapter cable.

5

The multimeter should indicate 0 Volt when the monitor is not in contact with water.

6

Lower the monitor into a vessel containing water. The multimeter should indicate 12 alt. 24 Volt.