Transmission downshifting at freeway speeds....

KD6ICZ · **Posted:** Mon Jan 13, 2014 11:21 pm

My 545RFE has acquired a new hobby. It momentarily (like less than a second) downshifts to 3rd when coasting in the 45 MPH range. It really jerks the vehicle.

The only thing I've done in the past few weeks is added 2 quarts of ATF. I did that because when the Suncoast TC was installed a year ago we only put 12 quarts in since by the best we could tell it looked full at the cold level. All reference guides say a complete fill is 14.1.

I noticed over time it was taking longer and longer to engage into gear in the morning when cold. So I figured it had lost a bit more fluid over the past 12 months since after the TC install it does leak from around the front seal a little.

Could adding the fluid cause the trans to make erratic shifts when coasting like that?

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geordi · **Posted:** Tue Jan 14, 2014 12:20 am

Full transmission change (when the torque converter is fully drained) can be as much as 19 quarts. What does your dipstick say?

Downshifting at highway speeds (45 isn't really highway speed now - that seems more like a bad 4-5 shift instead) is usually caused by the transmission computer rebooting - due to a scantool or other device plugged into the OBD port. This computer system doesn't play well with others. If you have a Bullydog, Scangauge, or something else... Remove it. You can't leave it connected all the time

The slow-engagement-when-first-starting-off has NOTHING to do with the fluid level. This is the very well known "Transmission drainback problem" and you should search on solutions for that. The only permanent solution I know of is an external check valve, installed on one of the lines. There is a thread about that somewhere in this section.

The transmission drains back to the pan while parked, and needs to re-fill the converter before you drive off. It will not fill effectively in park, but it WILL fill quickly in neutral. Put the shifter in Neutral and wait about 20 seconds, then drive away normally. It should be fine at that point.
As far as checking the fluid level, the fluid needs to be hot, and you need to check with the engine running and idling in park. If the level is not showing OR is massively over the 'full' mark... Then you need to make the appropriate change.

FYI: Even with just a filter-and-fluid change on the transmission, I needed to put in about 8-9 quarts before the transmission felt like it was performing properly to me. YMMV.

dkenny · **Posted:** Tue Jan 14, 2014 1:05 am

geordi,
I think you mean idling in neutral when hot..in park the pump doesn't work..
refer to you earlier statement about starting out cold..

so check the level in N not park..

if you have too much fluild in the tranny it can also cause strange symptons..the oil is areated..

-dkenny

geordi · **Posted:** Tue Jan 14, 2014 1:17 am

I could be wrong (as I don't have the dipstick or Jeep around to check) but I thought that it did want the fluid checked hot idling in park - I seem to remember the stick saying that.

If you park after running, but leave it idling, the torque converter is still spinning and fluid IS still moving around - just not at the speed that it does in neutral. There shouldn't be enough of a drainback at that point (especially if you just get right out and pull the stick) to make any difference. WHat you don't want to do is shut it off, because then the fluid certainly WILL stop moving and falling back to the pan from at least the valve body.

Foamy fluid certainly isn't good for the transmission anyway, too much can be just as bad as not enough fluid.

KD6ICZ · **Posted:** Tue Jan 14, 2014 2:16 am

geordi wrote:

Downshifting at highway speeds (45 isn't really highway speed now - that seems more like a bad 4-5 shift instead) is usually caused by the transmission computer rebooting - due to a scantool or other device plugged into the OBD port. This computer system doesn't play well with others. If you have a Bullydog, Scangauge, or something else... Remove it. You can't leave it connected all the time.

I think you nailed it! I work for Verizon Wireless in the Network department and occasionally they ask us to test new unreleased devices. I'm testing a newly released device (that's why I can talk about it) made my Delphi. It stays plugged in all the time and monitors the vehicle for malfunctions. This all did start after plugging that thing in. I will unplug it immediately and report it's not Chrysler capatible. I'm guessing this would be the case with any Chrysler vehicle.

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KD6ICZ · **Posted:** Tue Jan 14, 2014 2:29 am

As far a the N vs. P. It does say check in Park on the dipstick but my local dealer said check it in Neutral. All Chrysler transmissions have been Neutral since the beginning of time. So I'm thinking Chrysler got a great deal on surplus dipsticks from the Oldsmobile factory...

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geordi · **Posted:** Tue Jan 14, 2014 2:51 am

Before you go condemning a new device... It isn't ALL Chrysler products that behave in this manner. Just the CRD.

Most Chrysler vehicles have command modules that are all talking the same language, and all behave with each other. Whether that is the ISO protocols, or CANbus (all the new stuff) or generic OBD that they are all supposed to also speak... Doesn't matter - they all know the language and who the controller is.

For the CRD, however... The Body computer and the transmission both are speaking Chrysler (and want to be controller), the ECU is speaking Chrysler and Bosch protocols... The ABS might be Canbus... I am generalizing here, and Keith from Green Diesel Engineering can offer you a much more accurate list. Suffice it to say, the CRD has a very unique hodge-podge of computers that barely play nicely with each other on a regular basis.

Add in another control module that wants to join in the "conversation" on the cables... And all manner of mayhem is created. What happens is the timing circuits in the TCM get annoyed after a while, and the TCM just randomly reboots. It might take 3 miles, it might take 30. But it WILL happen, as you have experienced. Yes, this isn't a good thing.

But thankfully for your new device, it is only on the CRD that this happens. Just tell BigPhone that their new toy functions, but is not reliable for 2005/2006 Jeeps with a diesel engine.

KD6ICZ · **Posted:** Tue Jan 14, 2014 3:09 am

Got it! One thing I did discover with this device is how far off my odometer is. So far I've calculated my fuel mileage is about 10% than I thought.

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KD6ICZ · **Posted:** Tue Jan 14, 2014 3:21 am

As far as the fluid level it seems to have made a noticeable improvement to the quality of the shifts after adding the 2 quarts. Except of course when this random reboot would occur. But all other times the shifting is much more polished. I wish I had a way knowing if it's enough or too much.

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geordi · **Posted:** Tue Jan 14, 2014 3:30 am

You probably have the right amount in it now. The dipstick isn't terribly accurate (cheap off-the-shelf parts) and hits the bottom of the pan. Is it really so hard to imagine that they got the range in the wrong spot too?

Go with how it feels - that was how I did it, and it worked great.

Diver1430 · **Posted:** Sun Feb 09, 2014 10:31 pm

I had crd #2 downshift at 55 plus about twice a week. Pretty abrupt Of course it was six months after the extended warrenty But the xmission shop checked the unit and found some metal and he did some rebuild. But he brought in a computer guy who said it was the TCM
I bought a used TCM and the computer guy installed and I ve not had the problem since.

KD6ICZ · **Posted:** Mon Feb 10, 2014 12:20 am

Mine hasn't hiccuped one time since I removed the Delphi device. I've driven it almost 2000 miles since I removed it.

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bugnout · **Posted:** Mon Feb 10, 2014 3:37 pm

I had that same issue with the Scangauge. Random downshifts due to the TCM loosing sync with the ECM. Never had it happen unless the Scangauge was connected. I never leave the Scangauge connected for long while I'm driving.

Transmission downshifting at freeway speeds....

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