overdrive

[TwoToneX]

I am having a problem with my overdrive. Basically, it's not there. There's absolutely no difference in running my truck in either drive or overdrive, which is causing my rpm's to run too high. What would cause this and how might I go about fixing it?

 

[Opera House]

There are a couple components in the overdrive section that can have mechanical failure. If you have any sense of adventure, you can pull the transmission and work on just the OD section. If you can change brakes, this isn't any harder and would be about $100. Planetary gear can break welds ($50) or the OD drum can shear. This is such an easy fix if you have the logistics to do it. You can likely drive quite a while with this failure and wait for warm weather.

 

[MrShorty]

I would have to trust what Opera House says about the internals. From the descriptions he's written up before, it doesn't sound that difficult.
However, before I started pulling the transmission out and apart, I'd do some quick electrical tests and make sure the fault isn't in the EEC-IV control of the 3-4 shift. Is there battery voltage at the supply wire to the 3-4 shift solenoid at the transmission? Using the output state test, can the PCM actuate the solenoid?

 

[TwoToneX]

Thanks guys. I recently had some engine codes pop up and when I checked them through the self test with an ohmeter, there were three of them that popped up, one to do with the barometric pressure sensor and one to do with the 3-4 shift solenoid and one other I can't remember. When I took it to the shop, they cleaned up the MAF and replaced the barometric pressure sensor (MAP sensor) which seemed to take care of the codes so I thought it was fixed. Apparently this one is still around but I couldn't ever find it in my manuals, so where would I find it?

 

[MrShorty]

The 3-4 shift solenoid code (which number?) isn't very sensitive to faults in the system. Normally, only two cases that will set that code: A) If the 3/4 shift solenoid circuit is grounded upstream of the PCM, or B) If the circuit is broken upstream of the PCM. Faults in these circuits don't normally trigger a check engine light. Normally, they only show up in the KOEO hard fault test.
Basically what you need to do is get a wiring diagram that shows the 3/4 shift circuit and go over it carefully until you find the break/short/bad component. Note that the solenoid is inside the transmission mounted to the valve body. Don't discount the solenoid, it's possible it is shorted/open.

 

[TwoToneX]

We've been working on trying to get this fixed, I hope one or both of you guys subscribed to the thread. Anyways, I've been trying to track down a diagram with the 3/4 shift circuit, but can't seem to find one anywhere, even looked in the other threads on the site about the same thing. There are a couple in my Haynes manual, but they don't seem to be helping much. Is the PCM under the kick panel on the passenger side controlling it and we just need to find the pinout there? Otherwise, where should I be looking? Thanks in advance.

 

[Crankcase]

I lost overdive after a service once....Turned out somebody forgot to plug in a harness on the side of the tranny Maybe yours loosened off.

 

[TwoToneX]

That'd be sweet...Not that someone left it off, but it that's all it took to fix it. Sounds like something that would happen to me too, go through all this trouble and it ends up being a harness unplugged, hehe, I'll have to check them out tomorrow...

 

[MrShorty]

Sorry the ones in Hayne's don't work. For this particular circuit, I find the diagram in Chiltons is adequate. www.autozone.com has these diagrams in their repair guides. The PCM should be under the passenger kick panel, and part of getting the diagram is to find which pin controls the 3-4 solenoid. The other part of having the diagram is just to visualize the circuit so you can see how it's supposed to work.

 

[TwoToneX]

Hey Crankcase, is this what the wire harness looked like?

I think I might have taken care of this problem

 

[Crankcase]

HA! It WAS the plug? EF saves yet another tranny bill!