Table of contents: Contact pin #18 of the electronic…🠇 Electronic control unit contact pin…🠇 Electronic control unit contact pin…🠇 Electronic control unit contact pin…🠇 Electronic control unit contact pin…🠇 Ground contact pins #19, #14, #24…🠇
Checking the ECM electronic control unit (general check)
1. Inspect the ECU multi-pin connector for signs of corrosion or damage.
2. Make sure the connector terminal pins are properly installed and have good contact with the ECU multi-pin connector.
Voltage values at electronic control unit (ECM) connections
Note. Contact pin No. 19 of the electronic control unit is usually the ground of the electronic control unit for the Bosch Motronic MP3 electronic engine control system.2. 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 #18 of the electronic control unit
Note 1: The ECU pin #18 is directly connected to the battery (+) terminal, 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 ECU multi-pin connector should be folded back. The positive probe of the voltmeter is attached to the corresponding contact pin.
The electronic control unit is connected
1. Connect the positive probe of the voltmeter to the contact pin No. 18 of the electronic control unit. The voltmeter should indicate the nominal voltage of the battery (see note 2).
The electronic control unit is disconnected
2. Attach the negative probe of the voltmeter to the ground on the ECU.
3. Attach the positive lead of the voltmeter to pin #18 on the ECU. The voltmeter should indicate the nominal battery voltage (nbv).
Electronic control unit contact pin No. 27 (all cars except 306)
Note: Pin #27 of the ECU is connected to the ignition switch and voltage must be available when the ignition is on. On some models, the voltage from the relay goes through the immobilizer. If voltage is not supplied to pin #27, check the immobilizer circuit.
The electronic control unit is connected
1. The ignition is on.
2. Connect the positive probe of the voltmeter to the contact pin No. 27 of the electronic control unit. The voltmeter should indicate the nominal voltage of the battery (see note 2).
The electronic control unit is disconnected
3. The ignition is on.
4. Attach the negative probe of the voltmeter to the ground on the ECU.
5. Attach the positive lead of the voltmeter to pin #27 on the ECU. The voltmeter should indicate the nominal battery voltage (nbv).
Electronic control unit contact pin No. 37
Note: ECU pin #37 is connected to the main relay output terminal and voltage must be available when the ignition is on.
The electronic control unit is connected
1. The ignition is on.
2. Connect the positive probe of the voltmeter to the contact pin No. 37 of the electronic control unit. The voltmeter should indicate the nominal voltage of the battery (see note 2).
The electronic control unit is disconnected
3. The ignition is on.
4. Attach the negative probe of the voltmeter to the ground on the ECU.
5. Connect the positive probe of the voltmeter to the contact pin #37 of the electronic control unit. The voltmeter should indicate the nominal voltage of the battery.
Electronic control unit contact pin No. 36 (main control circuit of the relay)
The relay and electronic control unit are connected
1. Ignition is off.
2. Connect the positive probe of the voltmeter to contact pin #36, the device should show the nominal voltage of the battery (see note 2).
3. If there is no voltage, check the relay and relay wiring.
4. The ignition is 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. The relay is working: Check the voltage supply to the electronic control unit and its grounding. If the wiring is OK, then the Electronic Control Module (ECM) may be faulty.
7. Relay does not work: Check the relay and relay wiring.
Electronic control unit contact pin No. 3 (fuel pump relay control circuit)
The relay and electronic control unit are connected
1. Before starting this test, check the functionality of contact pin No. 36 of the electronic control unit (previous check).
2. The ignition is on.
3. Connect the positive probe of the voltmeter to contact pin No. 3, the device 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. The relay is working: Check the voltage supply to the electronic control unit and its grounding. If the wiring is OK, then the Electronic Control Module (ECM) may be faulty.
8. Relay does not work: Check the relay and relay wiring.
Ground contact pins #19, #14, #24 and #47 of the electronic control unit.
The electronic control unit multi-pin connector is connected
1. The ignition is on.
2. Attach the negative probe of the voltmeter to the ground on the engine.
3. Attach the positive probe of the voltmeter to the ground terminal, the voltmeter should indicate 0.25 volts (maximum).
The electronic control unit multi-pin connector is disconnected
1. Ignition is on or off.
2. Attach the negative probe of the voltmeter to the ground terminal.
3. Attach the positive probe to the No. 18 terminal of the ECU, the voltmeter should indicate the nominal voltage of the battery if the grounding meets the specifications.
Shielded wire signal
To reduce radio frequency interference (RFI) on some sensors (i.e. CAS, KS and OS) a shielded wire is installed. A shielded wire is connected to the electronic control unit to reduce interference to a minimum.