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Parasitic current draw measuring, B207

Symptom: - Car will not start. - Starter motor will not crank engine. - Low or no voltage from battery.

Parasitic current draw measuring, B207

Fault symptom

- Car will not start.

- Starter motor will not crank engine.

- Low or no voltage from battery.

Conditions

Low voltage can generate and store DTCs in the relevant system.

Diagnostic help

Check the charging system. See Alternator 120A, B207 , see test value.

Check the battery. See Battery, 60Ah or Battery, 70Ah or Battery, 85Ah . See also Battery Analyser/Battery Tester .

Make sure the parasitic current draw is measured on a fully charged battery.

Connect a multimeter with current clamp to the battery. Turn the ignition key to ON position. Then, turn the ignition key to OFF position. Remove the key from the ignition switch and lock the car. Wait for 25 minutes and then read off the current consumption, which should be less than 40 mA.

The diagram below shows that the control module components (1) are communicating actively on the bus. After about 20 minutes (2), the activity will subside and thereby also the current consumption. After 25 minutes (3), the current consumption should be lower than 40 mA.

The control module will wake up (4) at regular intervals to take measurements and perform checks.

Important

Measurements and checks carried out by the control module are subtracted from the measured parasitic current draw.