2003 Chevy TrailBlazer EXT 6-cyl. speedometer

I've gone to ski trip at around 7,000 ft, once before
Christmas and 2nd time after Christmas. During
2nd trip, my '03 Trailblazer speedometer went
beserk, like when I knew I wasn't over 30 mph,
it was reading 65 or something. When stopped,
speedometer would be stuck at 55 or close,
then 65 or so, etc. During these trips, I switched
between 2WD and 4WD few times, and have
used lower gear (2 or 3 instead of D) while cruising
long downhills.

A couple of days later, speed pointer would
backtrack 5 mph or so every time I turn off
engine, and eventually now it's back to zero
when engine off. It's like nothing ever happened.

It can't be high altitude. I would like to know
what may have been problem. Whatever was
the problem, it can happen again, I would think.
Any pointers? TIA.

There is a problem in the speedo heaed itself, not uncommon on this truck.
"grunt262" > wrote in message
oups.com...
>
> I've gone to ski trip at around 7,000 ft, once before
> Christmas and 2nd time after Christmas. During
> 2nd trip, my '03 Trailblazer speedometer went
> beserk, like when I knew I wasn't over 30 mph,
> it was reading 65 or something. When stopped,
> speedometer would be stuck at 55 or close,
> then 65 or so, etc. During these trips, I switched
> between 2WD and 4WD few times, and have
> used lower gear (2 or 3 instead of D) while cruising
> long downhills.
>
> A couple of days later, speed pointer would
> backtrack 5 mph or so every time I turn off
> engine, and eventually now it's back to zero
> when engine off. It's like nothing ever happened.
>
> It can't be high altitude. I would like to know
> what may have been problem. Whatever was
> the problem, it can happen again, I would think.
> Any pointers? TIA.
>
>



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