Component Tests and General Diagnostics

Checking the voltage / ground terminal

Power supply engine control module (ECM)
The engine control module (ECM) is powered via five power inputs on the control module.
With the ignition on, power is supplied to all voltage inputs and the engine control module (ECM) is in active mode.
1. Power input 1, terminal #B54 (#C54) is constantly supplied with power from the battery. This power input is used to power the memory in the Engine control module (ECM). In the event of an open-circuit, the engine control module (ECM) will be reset and adaptation values and diagnostic trouble codes (DTCs) and other information in the memory will disappear.
2. Power input 2, terminal #B27 (#C27) is temporarily supplied with power from the central electronic module (CEM) when the key is inserted in the ignition switch. This power input is used to prepare the engine for start-up, e.g. temporarily activates the system relay and the fuel pump. The engine control module (ECM) will not be activated if there is an open-circuit.
3. Power input 3, terminal #B30 (#C30) is supplied with power from the ignition switch via the central electronic module (CEM) with the ignition on. This power input is used to activate the system relay. The engine control module (ECM) will not be activated if there is an open-circuit.
4. Power input 4, terminal #B4 (#C4) is supplied with power from the system relay. The system relay is activated by the Engine control module (ECM) with the ignition on. This power input governs the supply of power to the Engine control module (ECM). The engine control module (ECM) will not be activated if there is an open-circuit.
5. Power input 5, terminal #B6 (#C6) is supplied with power from the system relay. The system relay is activated by the Engine control module (ECM) with the ignition on. This power input governs the supply of power to the throttle unit. In the event of an open-circuit, the engine control module (ECM) will be activated but the throttle unit will not be activated.

Checking the power supply
Check the power supply cable from the battery to the Engine control module (ECM) terminal #B54 (#C54). Check for an open-circuit. Check for loose connections. Check for contact resistance. Check for oxidation. The voltage must be approximately battery voltage.
Check the power supply cable from the Central electronic module (CEM) to the Engine control module (ECM) terminal #B30 (#C30). Check for an open-circuit. Check for loose connections. Check for contact resistance. Check for oxidation. The voltage must be battery voltage when the key is in the ignition switch.
Check the power supply from the system relay to the Engine control module (ECM) terminal #B30 (#C30), #B4 (#C4) and #B6 (#C6). Check for an open-circuit. Check for loose connections. Check for contact resistance. Check for oxidation. The voltage must be approximately battery voltage when the ignition is on.

Ground terminal engine control module (ECM)
The Engine control module (ECM) has four ground inputs that are all internally connected in the control module. See the relevant wiring diagram for further information about the ground terminal.
1. Ground input 1, #B1 (#C1) is power ground and is connected to the ground terminal in the body.
2. Ground input 2, #B2 (#C2) is power ground and is connected to the ground terminal in the body. See the relevant wiring diagram for further information about the ground terminal.
3. Ground input 3, #B3 (#C3) is power ground and is connected to the ground terminal in the body.
4. Ground input 4, #B5 (#C5) is power ground and is connected to the ground terminal in the body.

Checking the ground terminal
Check the ground cable between the Engine control module (ECM) terminal #B1 (#C1), #B2 (#C2), #B3 (#C3), #B5 (#C5) and the ground terminal. Check for an open-circuit. Check for loose connections. Check for contact resistance. Check for oxidation. With the ignition on, the drop in voltage between the ground connection for the control module and the ground terminal must not be greater than 0.5 V.
Remedy as necessary.

Other information
- Connecting the breakout box, B8444S Connecting The Breakout Box, Engine Control Module (ECM)
- Signal specification, B8444S Signal Specification, Engine Control Module (ECM)
- See the relevant wiring diagram for information about circuit and ground terminals in the bodywork
- Checking wiring and terminals Checking Wiring and Terminals

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