'99 4L80E OD problem

[KT]

Hi all, first I want to say that I have searched the forum for this and I have learned a lot about 4L80E problems, but none of them seem to be the same.

The vehicle is a '99 suburban 2500 6.5TD, 4L80E, 4.10s, 285/70R17, 152K.

All has been good until last weekend while pulling a heavy trailer (7500lbs) for the first time. Fist half of the trip all went well climbed hills left tranny in OD and it shifted down when needed, once or twice. On the return trip all was going well pulling up the hill in OD, the tranny shifted down towards the top, engine temp was up to about 210, and the tranny stayed there. All the other gears worked fine but no OD or TC lock up.

The hill climb is not huge, about 3000' over about 5 to 10 miles.

Got home unloaded and restart engine and all is fine again. I have to tow the exact load on the exact route at least three more times this year and I want to get in front of this problem before I burn anything up.

The tranny has been serviced on regular intervals, by the previous owner, (good looking fluid, not burned) but I don't know when the last one was, so that was where I was going to start.

Any synthetic ATF reccomendations?

I have seen a lot of issues with TPS, soleniods, and ignition replacements, but those all seemed to be with a 2nd gear limp mode.

Does anyone have the computer upgrade from HeathDiesel? I was considering the computer / Turbo controller combo pack. I believe the upgrade had a reprogramed tranny segment.

Anyone with load related OD and lock up problems / fixes

Thanks
Kirk

PS the tire swap only produced a 9% drop in RPM (60MPH is now at 1800 RPM. w/ 245/75R16 60MPH was 2050RPM).

[JohnC]

First thing to do is check the DTC's It almost certainly stored one from your last instance. Second, if it happens again, pull over somewhere convenient, shutdown and restart. It may well "go away".

[DA BIG ONE]

There is a manifold pressure switch (plastic housing) in there that monitors pressure, when they start to go bad you get strange shift glitches that go away then come back.

A good tranny shop will have the proper equipment to check unit, stay away form the stealer cause of high $$$$.

[bluuzman]

Hi all,

I'm also working on kind of similar problem. Every now and then (now more frequently) the TCC lockup and cruise stop working. Got code 28 and after a quick check it seemed that there was a problem in the main connector at the rear end of the transmission. It was clearly loose.

After disconnecting and fully plugging the connector back the code disappeared and transmission started working perfectly with smooth TCC lockup and cruise all right. This has happened a few times.

However, the problem is still there and I'm going to visit the shop again for scanning the DTC's and doing some debugging while having the scanner connected to PCM to find out if moving the connectors or cables make any difference. This is very difficult without the scanner.

It well may be the pressure switch but I have a strong feeling that it's some of the connectors or harnesses causing this.

Is there any typical connector that can be exposed to moisture and be subject to corrosion that might be involved here? It may sound odd but the problem first occurred this spring when I drove over some wet spots on the road. During the cold but dry winter weather there was no trouble at all.

-ari