Budweisman

I have a 1999 GMC Safari, trans was working fine until yesterday after driving for a while then all of a sudden tranny started to shift hard on second shift, like hitting a speed bump, it did it like about 7 to 8 times while I was driving. Had to stop and chedk the fluid, seems to be ok, I took off and it went away, after a while it shifted hard again on second gear. Today I went to goodyear and have them service my tranny and went to autozone to scan my DTC code, it says P1870, Manufacturer controlled transmission, any idea what this controlled transmission, anyway was able to reset it but any help is greatly appreciated, thanks

maxwedge

P1870 is a result of perceived slippage in the trans, when this happens the operating pressures are boosted by the pcm to try and compensate for the condition, there a several possibilities here, foremost is the tcc valve and bore in the valve body worn and causing the tcc to slip, this must have a comprehensive scan by a trans tech to determine the root cause.

Budweisman

Thanks for your quick reply, I think my next step is to take it to AAMCO for a free check up, not sure what a free check up includes, hopefully they might be able to trace the root cause.

MT-2500

I would be very cautious on a AAMCO free check.
You wiould be better off paying a good repair shop to check it out.
MT

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Remember proper testing gives us the answer to many problems.
MT

Budweisman

Hhmmm, that's probably why the guy was trying to drive me right away, anyway the tranny is still working fine, but I still want to have a reliable shop check it out just to be on the safe side, thanks.