What drives speed message to MCS unit?
 

2003 ML350

The other day, the volume kept going up even though I was not going fast enough to drive that. I reached over and turned the volume down, and since then no issue.

Today I hooked up my X431 DGS and low and behold, I had a fault code on the MCS - speed sensor fault.

What drives that fault?

Cruise control works fine, speedo works fine, abs works fine.

Thanks in advance!

The MCS's speed signal comes from the Transmission Control Module just behind the shifter in the center console. The speed signal is used by the MCS's Navigation Module, if installed.

The MCS volume is controlled by a microphone located in the overhead console near the trip computer and not the speed signal.

The speed signal that controls the speedometer and cruse control comes from a different source.

Individual speed sensors on each wheel controls the ABS and 4ETS.

Mike

DTC B1734 speed sensor is what is shown on MCS via a X431 DGS scanner. Does this give a hint as to what could be bad?

Anybody know how to troubleshoot this one?