Problem with my 1998 Chevy Tahoe codes = p1870
Checked the code "trans slipping". Checked fluid, full, and clean (red). I believe the fluid psi solenoid is bad. Normally the vehicle runs fine. Then when put under a load or driven hard (highway), the light comes on and the trans shifts funny. When the trans acts up, the 1-2 shift is very harsh, and a burning
smell is present. Upon sitting parked for around 1 hour, the trans is fine until you apply torque to it again. I will be changing the filter tomorrow, but would like your opinion.

P1870-component slipping, can be caused by a problem in the valve   body, but with that many miles on it, it may just be time to overhaul because  of slipping components, The condition of the fluid-if burnt, means trans.   needs to come apart and look for a failure. Again, with that many miles,   probably just worn out. Try the filter and fluid change to see if it helps. The   hard shifts are most likely caused by the line pressure being raised to  compensate for a slipping component.
1998 Chevy Tahoe P1870 Transmission Slipping

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