harald_richter5

Viano auxiliary battery woes

My Mercedes Viano diesel from is showing an auxiliary battery error. It has 197083 km on the clock. The speedometer displays an error, and there's a stored error code related to auxiliary power. Cranking is weak, and I'm seeing general car electronics issues. I suspect it's not charging. Has anyone else seen this on their car?

4 comment(s)

Sounds familiar. I had similar grief with my old BMW, a different car I know. Voltage drop was the culprit. Check your power management system isn't throttling the charge to the auxiliary battery. The IBS, Intelligent Battery Sensor, might be playing up. Have you measured the battery voltage when the engine is running?

IBS, huh? Where exactly is that located, and what voltage readings should I be seeing across the auxiliary battery with the engine running? I just want to rule out a simple bad connection before digging deeper.

On the BMW, the IBS was connected to the negative terminal of the main battery. On your Viano, it will likely be similar. As for voltage, you should see at least 13.5V, ideally closer to 14.4V, when the engine is running. If it's significantly lower, or fluctuating wildly, it points to a charging issue. If it is not the IBS I would advise taking it to a shop.

I appreciate the input. You were spot on. It ended up being a faulty auxiliary battery and associated charging circuit issue. The shop diagnosed it, replaced the battery, and sorted the charging issue. Total cost: 290€. The car electronics are behaving again.

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