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Pete
Pete, Car Enthusiast
Category: UK Car
Satisfied Customers: 24658
Experience:  Over 17 years experience diagnosing and repairing automobiles.
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Marty, hope you are well. I am fixing my crashed Mercedes

Customer Question

Hi Marty, hope you are well. I am fixing my crashed Mercedes ML250 cdi w166. I have replaced a new battery underneath the seat. I have also replace a new power steering rack motor and I managed to get the engine started. However, when I tried to make a slight turn on the steering wheel, it went crazy and couldn't stop turning and shaking on its own. I also noticed the display showing auxiliary battery malfunction. What do I need to do? Can I get some advices from you please?
Submitted: 10 months ago.
Category: UK Car
Expert:  Pete replied 10 months ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

Have you had the fault codes checked at all to see what codes are set with this issue here?This needs done with either a dealers sds machine or a scan tool that will plug in and communicate with all computers in your vehicle.

Let me know so we can continue,thanks Pete.

Customer: replied 10 months ago.
There are many fault codes appearing on the scan tools. But they are unrelated to the problem as far as I am concern because I haven't fixed some of the front end parts. I also came across the fault code on instrument display and also the scan tool whereby it showed auxiliary battery malfunction, I checked the battery at the back of the car and found it was indeed dead. Therefore I am very keen to know what does the auxiliary battery actually controls and does it have anything to do with airmatic thingy or power steering rack motor? Thanks.
Expert:  Pete replied 10 months ago.

The auxiliary battery is for the electronic shifter motor on the side of the transmission/gear box.This is in place in case the main battery fails this way you still have power to shift the vehicle into neutral to have it towed or pushed.If this battery is dead it needs replaced.

There is an update for the software in the power steering control unit for issues with the steering operation that should be checked into and done if needed.This has to be checked and done by a dealer who has access to an SDS machine to do this here.The bulletin number for this is LI46.35-P-054644.

In some cases the auxiliary battery being dead can cause issues with all electronics communicating properly and may cause other issues here possibly with the steering so it would be a good idea to start with replacing the auxiliary battery and then clear out all and any fault codes and see if the steering starts to work from there properly.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

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