Engine/Transmission (1998.5 - 2002) transmission or PCM?

[J.Post]

I've had a small problem for about 4 mos. Sometimes when driving down the highway my transmission will shift out of OD. It only happens when I'm when I'm in a coast or slight throttle. It has never happened under any significant throttle. It generally happens on the same stectch of highway where there is a slight down hill grade and I lift of the throttle slightly. As soon as I get back in the throttle it shifts back into OD.

After the first time this happened I took it to the transmission shop. They kept it for a day and could not replicate the problem nor did they find anything wrong w/ the transmission. Didn't even charge me anything for looking at if for a day and keeping it overnight.

I'm wondering if there is a connection problem w/ the ECM or if I'm experiencing the "electrical noise" problem. The odd thing is that it usually happens on the same strectch of road as described above.

 

[nps]

From what you describe it sounds more like you are going out of converter lockup, not shifting out of OD. You would expect to see about 100RPM change due to TC unlock. 300RPMs or more because of a TC unlock and downshift. Why do you think it is downshifting?



It is normal to shift out of converter lockup with no throttle (and cruise control off) because the TC goes into fluid coupling and you don't have as much retarding factor from the engine (saves fuel).



Could be noise interference if it happens at obvious times, like under throttle, but you say this doesn't happen.

 

[J.Post]

It's definitly down shifting. About a drop of 500 rpm when it does it.

 

[J.Post]

Anybody else?

 

[fox]

It could very easily be a bad connection. Check the harness from the trans up to the PCM. Find the wire that goes low to engage OD and connect a test light -at the dash and drive it. Have you put a noise filter on the PCM? Like DTT does?

 

[J.Post]

No noise filter. It didn't start until after I had a new stereo installed and I also installed a Sirius sattelite receiver.

It also is becoming more frequent.

 

[massdiesel]

Noise filter

Put a noise filter on it by your description thats what it sounds like you need we see it here in the shop alot.

 

[J.Post]

Put a noise filter on it by your description thats what it sounds like you need we see it here in the shop alot.

Where do I get a noise filter and where does it go on?

 

[massdiesel]

call me at 508 660 7093

 

[tractorface]

Did you unhook the batteries to install your new equipment. Any time you unhook the batteries you need to reset the APPS. Do a search resetting the APPS will most likely cure your problem, at least for a while.

 

[OL RATLR]

From what you describe it sounds more like you are going out of converter lockup, not shifting out of OD. You would expect to see about 100RPM change due to TC unlock. 300RPMs or more because of a TC unlock and downshift. Why do you think it is downshifting?



It is normal to shift out of converter lockup with no throttle (and cruise control off) because the TC goes into fluid coupling and you don't have as much retarding factor from the engine (saves fuel).



Could be noise interference if it happens at obvious times, like under throttle, but you say this doesn't happen.

I totaly agree with nps on this one.