Wont shift ie when running 40 mph tach is 3000/ When you let off though it coasts down as normal. Check engine light has never been on. Took it to auto zone they hooked up code reader and it wouldnt power...
NOTE:The transmission is on the same fuse as the MAF, O2 sensors and at
least one other sensor - if an O2 shorts out, it will blow the fuse and
the trans will go into limp-home mode. Be sure the trans has power and
the fuse is not blown before doing anything else.
Also note that many problems that show up as transmission issues are
actually PCM or electrical, and may be external to the transmission.
Try a different PCM, and check for chafing where the cables come out of
Secondly, 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 0.500" boost valve (easy fix in pan).
What is "limp-home mode" ? This is a fault mode in which the
transmission either loses electrical power or the PCM deactivates all
of the electronics. The transmission will default to max line pressure.
The driver will have Reverse and 3rd, with manual 2nd available by
putting the gearshift in 2 or 1 (doesn't matter). 1st, 4th, and TCC
lockup will not be available. It will not hurt the car to drive it like
this for short periods, but use manual 2nd to get the car moving, and
be aware that the trans will generate more heat than normal while
operating in limp-home mode due to increased torque converter slippage
during 2nd gear starts and no lockup in 3rd gear.
Trans shifts into gear harshly, car feels sluggish off the line,
No 1st, 4th or TCC lockup available, Manual 2nd, 3rd and Reverse are
only available gears, CEL is on: Transmission is either in limp-home
mode or has lost electrical power. If there are lots of error codes in
the PCM, check the fuse that powers the transmission, and if
it pops again, look for a short in that circuit like an O2 sensor
harness touching exhaust. Otherwise, check PCM codes for a particular
fault in the transmission causing the PCM to put it in limp-home mode.
Car goes into gear but feels very sluggish like the brakes are dragging,
but it will roll easily (starts out in 4th gear), you manually shift to
2 to get it moving, once it's moving you put it back in OD and the car
shifts 3rd to 4th on its own and locks the converter at the appropriate
time: ShiftB solenoid failed: Easy fix in the pan. Or a wiring problem
from PCM to trans.. or PCM.
Start with the simple things and check the fuse and Wire leads at the ECM's Transmission control module and the transmission it self. Look for any damages to the wire harness and leads. Try disconnecting the wire harness form the clip on the transmission and cleaning it with brake parts cleaner and reconnect and pull the Fuse to the ECM with the ignition on the on position "engine not running" for 10 sec and place back in and start the engine and go for a test drive and see if that reset the transmission. Good luck and keep me posted, we'll get your transmission running 100% again soon.
Jan 14, 2010 |
2001 GMC Sierra 2500HD