Q: transmission problems? on 2002 Chevrolet Express 3500

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the brake light on the dash came on, speedo dropped down to zero then came back, but was not accurate, security light on dash came on. would not shut down when I turned the key off.A noise sort of like a loose heat shield coming from under the vehicle. (transmission?)
(1) Answer
(3) Comments
the instrument panel may be failing. it can be checked by a shop with a scan tool. the first thing would be the connections at the back but being as you have multiple failures, i am leaning towards the instrument panel it self.

That does'nt explain the noise under the van. Maybe a faulty ignition switch?
the noise under the van could be a lot of things. the most common one is the cat converter shield vibrating.
as far as the ignition switch goes, it very well could be but must be confirmed with a diag from a shop familiar with these diags.

Thanks Roy, I took it to the shop so hopefully I will find out soon. I was told it coild be a crankcse sensor as well.