Hi I am new to this site I am am more fimiliar with Jeeps then my 99 Jimmy.

I am sure alot of you on her are fimiliar the dreaded DTC P1870.

Have any of you dealt with this issue. Is it an easy fix. I seem to have found mixed information that all I need to do is replace the solenoid. I would greatly appreciate any help on this.

Important
DTC P1870 is a type B code. The conditions for setting the P1870 DTC must occur on TWO CONSECUTIVE TRIPS (ignition cycles, with a drive cycle) before setting a P1870 history code.
When the conditions for setting DTC P1870 are met (first trip), the PCM commands maximum line pressure and harsh 1-2 shifts are the result.
This may result in a harsh 1-2 shift with no history code if the conditions for setting the DTC required for the second trip are not met, on two consecutive trips (Ignition cycles, with a drive cycle).

When the conditions for setting the DTC are met, on the second consecutive trip, a DTC P1870 is stored as a history code.
When the P1870 code is stored, the PCM will turn on the Service Engine Soon (SES), Check Engine Light (CEL), or Malfunction Indicator Lamp (MIL).
Correction
Install a control valve body with the revised TCC regulator and isolator valves. These valves are used in all transmissions produced after January 15, 1999 (Julian Date 9015), and all of the service parts currently available through GMSPO contain revised TCC regulator and isolator valves.

Important
If all of the following conditions are true, it is not necessary to rebuild the transmission or to replace additional transmission components beyond the control valve body.

Transmission operation is normal before the transmission reaches operating temperature, or before DTC P1870 is set (no slips, flares, or missing gears).
The torque converter is not blue or overheated.
The transmission fluid is not burned or has no burned odor.
The transmission fluid pan contains no abnormal debris (clutch material, bronze, brass, or metal fragments

 

There are quite a few threads on this subject with very much the same information.

 

Thanks all. I have read the threads. Was really wondering if any one tackled this themselves instead of paying a garage. Doesnt appear as if anyone has.

 

A valve body replacement is actually quite easy. You can also use the Sonnax kits to refurb your vb.

 

I have the same DTC P1870 on my 95 Blazer, symptoms are similar - hard 1-2 shift and, when transmission gets hot, no 3-4 shift. Also there is a DTC P0715 - Transmission overheat. Do you think is it the same problem?

 

P0715 is input speed sensor error and p0734 is gear raio error in 4th..i would try replacing the input sensor first..located in front of trans above solenoid pack..closet one to the engine..screws into trans..about 40 bucks..disconnect battery while replacing

 

The 4L60E transmission does not have an input speed sensor. The input speed sensor wasn't instituted in GM's line of light duty 4spd RWD/4WD automatic transmissions until the release of the 4L70E in 2006.

P0715 doesn't come up as a valid code for your vehicle, ToshK. Are you sure that was the code that came up? P0712 - TFT circuit low and P0713 - TFT circuit high are both valid codes for the transmission fluid temperature sensor.