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
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.
Jan 07, 2010 |
1999 Chevrolet Astro