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View Full Version : Trans slipping with no DTC code?


Extinct
February 23rd, 2011, 04:10 PM
Hey guys, working on my new to you 99 'Hoe. I'm hoping we have some transmission experts that can help me out a little.

My question is this, the transmission seems to slip like crazy in third and fourth gear, but I don't have any DTC codes when I check it with a scanner. That does not seem right to me? Shouldn't it throw a DTC 1870 slipping code?
joecar
February 23rd, 2011, 04:13 PM
Hi Extinct,

It may throw a code, but not necessarily.

Do you have any log files...?
Extinct
February 23rd, 2011, 04:24 PM
No log files yet, but I was thinking of taking it out and logging. I've not worked on one of these L31's before, do they have a separate TCM or are all the PID's available once you connect to the PCM? I assume I would want to mostly log transmission values and engine rpm?
ScarabEpic22
February 23rd, 2011, 06:59 PM
Its going to have the Vortec 98-00 PCM aka Vortec Black Box PCM. So engine and trans params in the same controller.

My 02 TrailBlazer slipped like crazy and finally threw a code, but it was doing it for weeks before it finally did.
Extinct
February 24th, 2011, 12:01 AM
Its going to have the Vortec 98-00 PCM aka Vortec Black Box PCM. So engine and trans params in the same controller.

My 02 TrailBlazer slipped like crazy and finally threw a code, but it was doing it for weeks before it finally did.

So what turned out to be the problem, was it a worn clutch?
slow67
February 24th, 2011, 05:09 AM
If the trans doesn't have an ISS sensor, it will only detect a slip if the converter is locked up (and it takes 2 key cycles at that).
ScarabEpic22
February 24th, 2011, 09:31 AM
So what turned out to be the problem, was it a worn clutch?

I messed up a shift kit and OD servo install. Lost 4th gear, then TCC lockup, then 3rd gear. Took it to a trans shop and the builder went through the valve body and installed a new kit properly. Never had the trans rebuilt, still running the factory clutches from 02 with 120,6xx mi on it. The 4.2L I6 doesnt make enough power to really abuse the 4L60Es too bad.
Extinct
February 26th, 2011, 03:14 PM
Went out an got some data on it, although I don't think it will show a lot. I can post the logs here.

Interesting occurance during the test drive though. Trans slips badly in 3rd and 4th, but if I "wing" the throttle a little, it seems to grab better as the throttle slams shut, just for a second. Almost like the 3-4 piston/clutch apply is enhanced during that time period, like more pressure is being applied.

Could it be a 3-4 accumulator problem?
slow67
February 28th, 2011, 04:26 AM
Went out an got some data on it, although I don't think it will show a lot. I can post the logs here.

Interesting occurance during the test drive though. Trans slips badly in 3rd and 4th, but if I "wing" the throttle a little, it seems to grab better as the throttle slams shut, just for a second. Almost like the 3-4 piston/clutch apply is enhanced during that time period, like more pressure is being applied.

Could it be a 3-4 accumulator problem?

Probably slipping 3-4 clutches. 95% of the time, this is first to go in a 4L60. I'd bet the increased pressure is helping them hold on the 2-3 shift (and they stay on for the 3-4). Its only a matter of a short time before they completely let go.