Checking Supply Voltage/Ground Terminal, Engine Control Module (ECM)

Checking the voltage / ground terminal

Checking the power supply and ground terminals

Power supply engine control module (ECM)
The engine control module (ECM) is powered via four power inputs on the control module.
When the ignition is on, all four power inputs are powered and the engine control module (ECM) is in active mode.
1. Power input 1, terminal #B54 (#C54) is supplied with power via a fuse 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) will disappear
2. Power input 2, terminal #B30 (#C30) is supplied with power via a fuse from the start control module (SCU), ignition position II (KL15, "wake up"). This power input is used to activate the engine control module (ECM). When power input 2 is powered, the system relay will be activated and power inputs 3 and 4 will be powered. The engine control module (ECM) will not be activated if there is an open-circuit
3. Power input 3, terminal #B4 (#C4) is supplied with power via a fuse from the system relay. The system relay is activated by the engine control module (ECM). This power input governs the supply of power to the engine control module (ECM)
4. Power input 4, terminal #B6 (#C6) is supplied with power via a fuse from the system relay. The system relay is activated by the engine control module (ECM). This power input governs the supply of power to the engine control module (ECM).

Checking the power supply
Check the power supply cable from the battery to engine control module (ECM) terminal #B54 (#C54). Check for an open-circuit. Check for loose connections. Check for contact resistance. Check for oxidation. Check the fuse. The voltage must be approximately battery voltage.
Check the power supply cable from the start control module (SCU) to engine control module (ECM) terminal #B30 (#C30). Check for an open-circuit. Check for loose connections. Check for contact resistance. Check for oxidation. Check the fuse. The voltage must be approximately battery voltage when the ignition is on.
Check the power supply from the system relay to engine control module (ECM) terminals #B4 (#C4) and #B6 (#C6). Check for an open-circuit. Check for loose connections. Check for contact resistance. Check for oxidation. Check the fuse. The voltage must be approximately battery voltage when the ignition is on.

Ground terminal engine control module (ECM)
The engine control module (ECM) has three ground inputs. All ground inputs from the control module are connected via three separate ground leads to the same ground terminal in the car body. See the relevant wiring diagram for further information about ground terminals.
1. Ground input terminal 1, #B1 (#C1), is power ground and is connected to the ground terminal in the car body
2. Ground input terminal 2, #B2 (#C2), is power ground and is connected to the ground terminal in the car body
3. Ground input terminal 3, #B3 (#C3), is power ground and is connected to the ground terminal in the car body.

Checking the ground terminal
Check the ground lead between engine control module (ECM) ground terminals #B1 (#C1), #B2 (#C2) and #B3 (#C3). 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 engine control module (ECM) and the ground terminal must not be greater than 0.5 V.
Remedy as necessary.

Other information
- Connecting the breakout box Connecting The Breakout Box, Engine Control Module (ECM)
- Signal specification Signal Specification
- 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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