1996 Tahoe trans trouble code 1870?

limited info generic answer ----check fluid level and condition ---look and examine the shifter cable connector known to rust out ---have scanned for any pending or active trouble codes ---is it 4x4 if is check that not neutraled at transfer case --

1870 is a transmission error code which indicates excessive wear in the valve body and is usually accompanied by unusual shifting. This is a problem requiring a shop fix unless you are familiar enough with transmissions to attempt the repair yourself. You can go to transmissioncenter.net and you will find the part which will fix this error code from recurring. Unfortunately, you may have to have the transmission rebuilt. I am not affiliated w/PATC, but they are the best source for parts, builds and advice there is for GM 4L60E transmissions.

Diagnostic trouble code P1870 (Transmission Component Slippage) is a General Motors-specific code whose set parameters are determined by transmission type and engine size. The PCM monitors and compares engine speed to vehicle speed after the converter clutch has been commanded ON in either high gear or Overdrive. Should the expected rpm ratio exceed predetermined parameters, DTC 1870 sets. And upon doing so, the PCM elevates the transmission main line pressure and stops converter clutch apply.

Once the vehicle has made it to a cruise state, the PCM then begins to monitor the vehicle's cruise ratio. If at some point the transmission begins to slip, P1870 sets and line pressure is elevated in an attempt to stop any further slippage and prevent further damage. This would explain why DTC 1870 Ls often accompanied by a complaint of a hard 1-2 up shift.

When this code sets, it could have any number of causes, ranging from the sump running low of fluid to a malfunctioning torque converter. Take a GM 4L60-E transmission, for example. When it's in Overdrive, the forward clutch and the 3-4 clutches are applied, as well as the 2-4 band. Now add the converter clutch. This is what the PCM monitors at cruise. If the ratio breaks away, the cause could be any of three components, the hydraulics that operate them or the electronics that control them. Fortunately, experience has shown that in most cases, the cause can be traced to some form of converter clutch failure as a result of valve body concerns. With GMs 4L80-E transmission, this code has usually been the result of a cracked converter clutch piston.

Put a line pressure gauge ($55 shipped on Ebay, or visit a local trans shop) on the pressure test port and go for a drive to verify proper line pressure. Base pressure at idle in P,N,OD should be around 70psi and around 140psi in R. Max line pressure should be at least 190psi at WOT in 1st or 2nd, 225psi is optimum. If base pressure is low, trans or pump is worn out. If max pressure is low, check EPC solenoid. If reverse is slow to engage, and line pressure does not come up to at least 130psi in reverse, replace the boost valve with a Transgo 0.049" - 0.500" boost valve (easy fix in pan), and replace the servo with an upgrade servo from a Corvette 4L60E. This will give you a more firm shift and address the DTC 1870 which is common to a weaken Boost valve or faulty EPC valve.

There have been issues with worn engine/ transmission mounts allowing the tranmission to come into contact with the cradle causing wear or breakage of the case. Replace trans if not a cover that is cracked and ensure engine and trans mounts are in good condition.

input shaft in gearbox has failed

P0140 Oxygen Sensor Circuit No Activity Detected (Bank 1 Sensor 2) P1192 Post-catalyst Fuel Trim System Bank 1

Replace the O2 sensor after the catalytic Converter and check to make sure the wire harness and clips are not damaged. Also check the O2 sensor fuse in the fuse panel to make sure there not blown. 
As for the p0700 code is a generic code and the ECM needs to re-calibrated for the performance upgrade in your transmission. It's common to happen when there are changes like the transmission fluid pressure has been altered which would give it a better and firmer shift, but the transmission reads the higher line pressure as a problem. If you take it to a good transmission shop with a tech2 scanner, the tech2 can change the transmission ECM parameters and that way it will recognize the higher transmission line as a norm. 
Have done a few upgrades on the 4L60E with a common swap of the servo's with a corvette servo's ($45.00) to firm up the shift and raise the transmission line pressure to keep the slipping to a minimal and also bring down the shift points at WOT on the 1st-2nd shift to get going a bit faster (used Tech2 scanner). 
Good luck and keep me posted, be glad to help.

The key distinction of the Later 4L60-E (1997-2006) from the Early 4L60-E (1992-1997) or 4L60 (1990-1992) or 700R4 (1982-1989) is the six-bolt "hex" rear output or tail housing / adapter pattern. The previous versions featured a four-bolt square bolt pattern at the adapter or tail housing. This is where that made the small change and the 96/97 year was a change over year so you may have the newer housing or the older housing, but if your replacing the transfer case with the transmission your good to go, the electronics are the same. Just the body housing is different. Good luck and hope this helps. And why wold you want to convert the transmission, there are lots of easy simple up grades with out dropping the transmission or valve body. 

It is a 4L60E , electronic trans. The same trans fits 93 through 99 old body style Tahoe, Suburban, and Pick up's. Good Luck

Sounds like a speedo gear in the transmission ... I think the tahoe one had a speedo cable the speed sensor is located in the speedo ... will cause all those to fail if speedo is not working as did in my Astrovan

The transfer case has a motor mounted on the exterior of the transfer case,and they do go bad.There is also a transfer case controller (computer) that is part of the Body Control Module (BCM) and i have seen where a malfunctioning "door" open or closed sensor would cause the transfer case controller to inhibit,or,not allow 4WD engagement.Long story short is,scan the vehicle computers for trouble codes,including the BCM,and repair any codes present.If codes are repaired and still no 4WD,test the electric motor that is mounted on the transfer case.When all external controls are operational and tested as operational,the last conclusion would be an internal transfer case malfunction,but as a last resort.This is why it is important to verify and/or repair all external controls,inputs,and commands.The particular transfer case in your Ford has an aluminum case half that is prone to wear,and i shim out the excessive end play as part of the rebuild,so overhauling it in your garage does require more than meets the eye.Good luck.