Downshifting issue

[grt]

my 2000 Grand Prix Gt has issues, when i let off the gas on the highway and the tranny downshifts the rps jump up for a second and then again each time it downshifts. Any idea if this is a trans issue or a fuel issue?

[rickisrad]

sounds like a trans issue to me. check the fluid level and condition.

[grt]

trans fluid is good and clean

[grt]

i just plugged in the code tester and get a P1860 code, does this have to do with the downshifting issue? Help?

[BNaylor]

A P1860 transaxle DTC means there is an issue with the torque converter clutch pulse width modulation solenoid.(TCC-PWM). Its located inside the tranny side cover (driver's side). Also, when that solenoid acts up it will inhibit TCC operation like lock and unlock which explains the erratic rpms during downshifting.

[grt]

is this something that can be replaced by me, or does the tranny need to come out? Is it an expensive part?

[BNaylor]

You can try DIY but technically the work is difficult and tedious. The transaxle can stay mounted but alot of stuff has to come off on the driver's side suspension/drivetrain to get the side cover off.

The other thing to try is remove the 25 way electrical connector located on the driver's side front of the tranny. Look for corrosion and clean with electrical contact cleaner. Let dry and then reconnect. All the commands from the PCM module to the solenoids and power are at this connector.

See thread below for exact location of solenoids and PCS.

http://www.automotiveforums.com/vbul...d.php?t=760735

[Tech II]

Also look for possible damage to the transmission harness.....could have a rub though condition where the harness rubs up against a stud bolt or sharp object....

[grt]

i cleaned all the connectors and checked the wiring all of which looks fine, but its still doing it. Just wondering how serious this issue is and will it get worse or cause more damage if i was to leave it for awhile?

[BNaylor]

It depends. Any issue such as this could cause more damage or it may not. In many instances of P1860 in automatic mode the car will start in second gear and 4th gear overdrive may be inhibited so check that. With the TCC acting up and no 4th your fuel economy will get bad so there are other issues to consider. Just so you know the fix for most P1860 problems is TCC-PWM solenoid replacement.

[grt]

4th gear is still working, the TCC is locking and all other gears are working normal, its only when i let off the gas after being in 4th that the rpms jump while downshifting, as long as it don't get worse I guess i can live with it for now, money is tight!