Transmission Problem

[01 Suburban LS]

Hi, Im new here, I just bought a 2001 Suburban LS, but my question is not about my Suburban, but a friends. She just bought a 1997 Suburban and its having some tranny problems. Specifically, while driving the Service Engine Soon light comes on, usually after driving quite a while, then it has really hard 1st to 2nd shifts, and slightly less hard 2nd to 3rd shifts. After turning the Suburban off and letting it sit a bit, the light stays on, but the hard shifts go away.

 

After connecting an OBDII diagnostic scanner it comes up with a DTC P1870.

 

Any ideas what needs fixing?

 

Thanks

 

Mike

[MoJo]

P1870

Transmission Component Slipping/ Transmission Mechanical Transfer Case 4x4 Switch Circuit Failure

[robsawatsky]

The computer is detecting slipping in the tranny so it is cranking up the shift pressure to max to eliminate as much slipping as possible so as to minimize further tranny damage and total failure.

 

It is possible there is a sensor problem and not a real tranny issue, but this could easily be some tranny repairs required. Make sure tranny fluid is properly filled and check for colour and smell. If it is dark and burnt looking/smelling, then a slipping tranny is almost for sure the problem.

[willfxp]

How do you fix a slipping tranny? Like a $200 fix or $1000 fix?

 

I noticed mine will sometimes shift harder, usually from 1 to 2.

 

Thanks,

[gmcsid]

P1870 is set when the slip speed is too high when the torque converter clutch is commanded on. This happens when driving on the freeway. When the P1870 sets TCC is inhibited and max line pressure is commanded causing harsh shifts. Anything in the transmission could be slipping, but the most common cause is wear in the valve body that causes the torque converter clutch circuit to leak. If the fluid looks good and you have not noticed any other problems you should look into replacing or repairing the valve body. A good transmission shop will be able to do it either way. It's around a $500-$700 fix.