Checking the electronic control unit ECM (general check)
1. Inspect the multi-pin connector of the electronic control unit for signs of corrosion and damage.
2. Make sure that the connector terminal pins are properly installed and make good contact with the multi-pin connector of the electronic control unit.
Voltage values for the connections of the electronic control unit (ECM)
Note. Pin #19 of the ECM is normally the ECM ground for the Bosch Motronic MP3.2 ECM. For this reason, if possible, pin #19 should be used to connect a voltmeter or oscilloscope. If pin #19 is not available, other ground pins can be used.
Contact pin No. 18 of the electronic control unit
Note 1. Pin #18 of the ECU is directly connected to the terminal (+) battery, so voltage is available when the ignition is off.
Note 2: When measuring voltage at a multi-pin connector, remember that the terminals are in reverse order. The multi-pin connector remains connected to the component, and the insulation of the multi-pin connector of the electronic control unit should be bent. The positive probe of the voltmeter is attached to the corresponding contact pin.
Electronic control unit connected
1. Connect the positive voltmeter lead to pin #18 of the ECU. The voltmeter should indicate the rated voltage of the battery (see note 2).
Electronic control unit disconnected
2. Attach the negative voltmeter lead to ground on the electronic control box.
3. Attach the positive voltmeter lead to pin #18 on the ECU. The voltmeter should indicate the rated voltage of the battery (nbv).
Pin number 27 of the electronic control unit (all cars except 306)
Note. Pin #27 of the ECU is connected to the ignition switch and voltage should be available when the ignition is on. On some models, the voltage from the relay passes through the immobilizer. If voltage is not being supplied to pin #27, then check the immobilizer circuit.
Electronic control unit connected
1. Ignition on.
2. Connect the positive voltmeter lead to pin #27 of the ECM. The voltmeter should indicate the rated voltage of the battery (see note 2).
Electronic control unit disconnected
3. Ignition on.
4. Attach the negative voltmeter lead to ground on the electronic control box.
5. Attach the positive voltmeter lead to pin #27 on the ECM. The voltmeter should indicate the rated voltage of the battery (nbv).
Pin number 37 of the electronic control unit
Note. ECU pin #37 is connected to the main relay output terminal and voltage should be available when the ignition is on.
Electronic control unit connected
1. Ignition on.
2. Connect the positive voltmeter lead to pin #37 of the ECM. The voltmeter should indicate the rated voltage of the battery (see note 2).
Electronic control unit disconnected
3. Ignition on.
4. Attach the negative voltmeter lead to ground on the electronic control box.
5. Connect the positive voltmeter lead to pin #37 of the ECM. The voltmeter should indicate the nominal voltage of the battery.
Pin number 36 of the electronic control unit (relay main control circuit)
Relay and ECU connected
1. Ignition off.
2. Connect the positive probe of the voltmeter to pin No. 36, the instrument should show the rated voltage of the battery (see note 2).
3. If there is no voltage, check the relay and relay wiring.
4. Ignition on. The voltage should drop to almost zero.
5. If not, disconnect the ECU multi-pin connector and connect a temporary jumper wire from pin #36 to ground.
6. Relay working: Check the voltage supply to the electronic control unit and its grounding. If the wiring is good, then the electronic control unit may be faulty (ECM).
7. Relay not working: Check relay and relay wiring.
Contact pin No. 3 of the electronic control unit (fuel pump relay control circuit)
Relay and ECU connected
1. Before starting this test, check the operation of pin No. 36 of the electronic control unit (previous check).
2. Ignition on.
3. Connect the positive probe of the voltmeter to pin #3, the meter should show the nominal voltage of the battery (see note 2).
4. If there is no voltage, check the relay and relay wiring.
5. Turn the crankshaft or start the engine, the voltage should drop to almost zero.
6. If not, disconnect the ECU multi-pin connector and connect a temporary jumper wire from pin #3 to ground.
7. Relay working: Check the voltage supply to the electronic control unit and its grounding. If the wiring is good, then the electronic control unit may be faulty (ECM).
8. Relay not working: Check relay and relay wiring.
Ground pins No. 19, No. 14, No. 24 and No. 47 of the electronic control unit.
Multi-pin connector of the electronic control unit is connected
1. Ignition on.
2. Attach the negative voltmeter lead to ground on the motor.
3. Attach the positive probe of the voltmeter to the ground terminal, the voltmeter should indicate 0.25 volts (maximum).
Multi-pin connector of the electronic control unit is disconnected
1. Ignition on or off.
2. Attach the negative lead of the voltmeter to the ground terminal.
3. Attach a positive test lead to pin #18 of the ECU, the voltmeter should indicate the nominal voltage of the battery if grounding is within specification.
Shielded wire signal
To reduce radio frequency interference (RFI) on some sensors (those. CAS, KS and OS) shielded wire is installed. A shielded wire is connected to the electronic control box to keep interference to a minimum.