hello, my wife has a 97 monte ls with about 175K on it, i changed the tranny fluid/filter at 100K. over the past year the check engine light has come on and the code has always been P1870 which is some sort of tranny slippage code. my wife only drives the car about 5 miles to work and back and just running around town, she doesn't get a check engine light until she drives the car more than 30 miles in a stretch, i clear the code when she comes home and nothing happens for however long until she drives that far again. she says she has not noticed any abnormal shifting or anything when this happens. i dont understand why it would do this, why doesnt it do it all the time? especially in stop and go traffic?

 

DTC P1870 Transmission Component Slipping


The GM transmission in your vehicle has a history of the Torque Converter Clutch (TCC) relay or apply valve sticking when hot causing a harsh shift condition. A company called Sonnax makes a replacement valve and kit to fix this condition. The kit has an oversized valve, spring and sleeve as well as a reamer to increase the bore diameter to match the new oversized valve.

First have the transmission pan dropped and examine the filter, fluid and valve body for metal shavings. Excessive amounts of metal and clutch material and burnt fluid indicate excessive transmission wear and it will have to be overhauled or replaced. Next, examine the valve body and valves for scoring on bore surfaces and valves loose in their bores. The above mentioned kit may fix a bore, but the entire valve body should be replaced if scoring and loose valves are found in several valves. Have the transmission fluid power flushed, not just drained, and reassemble.

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