SureTrack Real Fix: Take a Seat

Here’s another case of a customer complaining that their car won’t start, but it’s actually because the battery is below the required voltage. In this case the battery wasn’t faulty so it’s either not being charged properly or something is draining it. Follow this Real Fix to see how a parasitic draw was tracked down and repaired on this Mercedes-Benz C300.

Vehicle
2008 Mercedes-Benz C300 4Matic 3.0L

Title
Engine Does Not Start, Replaced Seat Adjuster Switch

Complaint
The customer states the engine will not start.

Cause
Confirmed the customer’s complaint and found the engine did not start. Performed a visual inspection of the battery and battery terminal, but found no obvious faults. Used a multi-meter to measure the voltage across the battery terminals and found the measured voltage was below the specified range. Connected a battery charger to the battery and charged the battery. Used a battery conductance tester to test the battery and found the battery was able to conduct the specified amount of current, which verified there were no faults with the battery. Connected an inductive ammeter around the negative battery cable to measure the parasitic draw on the battery and found the measured excessive parasitic draw was no longer present when the seat adjuster fuse was removed. Disconnected the seat adjuster switch connector, visually inspected the connector and terminals and found no obvious signs of damage. Used the multi-meter to check for continuity across the seat adjuster switch and found the switch had continuity when none of the seat adjuster switch buttons were depressed. The results of these tests verified the seat adjuster switch was faulty.

Correction
Replaced the seat adjuster switch and verified the vehicle operated properly. The customer’s concern did not return.