Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DC/DC converter
Due to the considerably more frequent occurrence of starting operations, the electrical load that occurs often leads to voltage dips in the vehicle electrical system. To stabilize the supply voltage for certain voltage-sensitive electrical components and protect them, a DC/DC converter is used together with the automatic engine start-stop. The DC/DC converter supplies the terminal 30 relay with constant voltage, also during the starting operation.
The graphic below shows the DC/DC converter using the example of E90.
| Item | Explanation |
|---|---|
| 1 | Trim panel, electronics box |
| 2 | DC/DC converter |
| 3 | 10-pin plug connection |
The DC/DC converter needs the following signals:
- Terminal 50
- Terminal 15
- Terminal 30 (possibly model-specific variants).
The DC/DC converter transmits the following encoded information for the diagnosis (pulse-width modulated signal):
- DC/DC converter OK
- DC/DC converter faulty
- DC/DC converter overheated.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.