Vehicle: 2018 BMW X5, xDrive 40e, AWD (F15), L4-2.0L Turbo (N20), Hybrid
Mileage: 115,744
Problem: The auto start/stop system was inoperative. The customer stated that they must hold the start button for five seconds for the engine to start.
Case Details: The technician pulled diagnostic trouble code (DTC) 21A515 - Start system, toothed belt starter: Timeout, automatic engine start-stop function deactivated. Not having a lot of BMW experience, he called ALLDATA Tech-Assist.
The Tech-Assist consultant recommended starting the diagnosis by checking the auxiliary battery first. It is responsible for the vehicle’s start/stop function. The tech inspected the auxiliary battery and found it failed a load test; only recovering to 2.0 volts.
Confirmed Repair: He replaced the auxiliary battery and registered it with the Digital Motor Electronics (DME) module. After that, the engine start/stop function was restored. Easy Fix!
The ALLDATA Tech-Assist team fields cases like this every day. See how Tech-Assist can help your shop save time and money with on-call diagnostic support from ASE-certified Master Technicians. More Tech Tips
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