Vehicles equipped whit a 4 speed automatic transmission may develop a harsh 1-2 shift and/or illumination of the Check Engine Light with code P1870 stored. This can be caused by wear of the bore for the TCC isolator and regulator valves in the valve body. This condition does not commonly occur until the transmission reaches normal operating temperature. If the valve body is worn, replacement will be necessary to correct this concern.
Check Engine Light With Code P1870 on Chevrolet Astro
Average mileage: 152,577 (113,000–216,145)
Drive Trains affected: AWD, RWD
15 people reported this problem
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My van is doing the same thing. It has a Check Engine Light that is always on with a P1870 code stored. The computer seems to reset after every drive cycle (turn the engine off and let it sit for a few minutes), but the transmission enters the so-called "lockup" whenever I spend a significant period of time (more than like 10 minutes) at high speed (above 50mph). After that threshold is reached, the transmission performs very poorly until the engine is shut off. If you stop at a red light, the engine sounds like it's struggling to maintain a normal idle because the transmission is trying not to disengage. Furthermore, when I pulled the transmission dip stick the other day, it looks like it's burning up. The fluid is far from clean and there are deposits all along the dip stick. I have already replaced the valve body, fluid, and filter and the check engine light came right back on when I got on the freeway. Is there another simple fix before going down the complete rebuild road?
Same problem with mine
Hard 1-2 shift when hot. Initially on check engine. Now has the p1870 code.