Chev auto trans slow taking off

SOURCE: voltage intermittent, engine missing at all speeds, affect auto trans. shifting, kills hot or cold

The charging system, pedal, and sensors have been checked. The trans. problem and missing problems were the original problems and when my mechanic finally sent me to Chev. none of the problems " choose to show themselves." I should know on Mon. if my mechanic has solved the problems with the greater number of symptoms. Keep me in your files. More later-  Bill

SOURCE: 1995 tahoe auto trans

Sounds like you may have smoked high gear clutches. Check your fluid and see if the color is darker than normal and smells burnt...

SOURCE: 1997 chey pu auto trans 1st and 2nd shift good

Do you get a check-engine light, or does the transmission O/D light flash? Many times, this is due to a speed sensor on the transmission. When the sensor goes, the transmission has to do default shift timing and it will shift very late. Usually, this will set a code in the onboard computer.

SOURCE: 1993 4l60e - Shifts hard on the 1-2 shift, works fine otherwise.

Did you change the transmission filter and gasket as well as the transmission oil before running your truck.

Harvey N Tawatao

• 3854 Answers
• Posted on Jan 07, 2010

SOURCE: reset code trailer towing may set code gm 4l60E

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.