Wet1

My auto trans has decided to not shift into OD. It started out intermittently and now wont go into OD at all (although the light on the button comes on). I don't drive the truck much, but when I do it sure sucks driving the thing at 3000 rpm on the hwy (at about 5 mpg)!

A buddy mentioned it's probably a lose connection at the trans or a bad solenoid. I wiggled all the connections at the trans that I could find, but that didn't seem to help.

Anyone have any insight as to what's likely wrong? The solenoid suggestion sounds possible, but I have no idea what it looks like or where it's located...


Thanks in advance for any help you might be able to offer.

John Faughn

All diagnostics should start with the basics , fluid level , is the fluid still red-not burned ?
The light means it is off , at least on truck , push the button .
Then it is controlled buy the computer , under the right conditions , speed above about 45 MPH , temp sensor [ in trans line ] telling the computer that the fluid is above 40*F , then the throttle has to be not pulling / no load , the brake sw. turns the cruse off & unlocks the , lockup , mine had this issue when I bought it .
Having a wiring diagram so that you can see if the switch is getting the signal from the computer with all the other specs set , as above .

cdennyb

OK, here's my story... my 03, (don't know if this would apply to your older model or not...) did exactly the same thing. On occassion, it'd shift... sometimes not. One morning I'd start up and it'd work great, next morning not.
I changed the TPS and it seemed to help, i thought. 3 days no problems, then right back at it... one day yes, one day no.
Now... the solution...

The PCM, located on the passenger side of the firewall had three big connectors going into it. One went to the ECM of the engine, the other went to various sensors, etc. and the final one, to the transmission, etc.
I took contact cleaner and sprayed the plugs and connectors several times over the course of a few days and to my pleasant surprise I haven't had a single issue since then. Those plugs are very susceptable to corrosion on a microscopic level i guess and that fixed the contact isses. If I ever have any issues with things working one day and not the next... contact cleaner and work the dicken out of those connectors first. everything else is just dollars and sense.


hope this helps..

db

JonnysDodge

Mine had the same problem as well, the sensor at the front of the truck, my mind sucks I can't remember the name of it, anyway it was bad, and the gap was set wrong. I had it replaced and had the gap set right, and it fixed the problem. If I remember the name I will post it. Sorry again for the name.

oldblues

hi
sugest you clean or replace your T P S

Wet1

Some good info here, thanks guys. I did check the TPS last year when I first had this problem, it seemed okay. I guess I should check the conections at the computer next.

Wet1

Fluid is okay. OD doesn't work with switch on or off.

How do you test the temp sensor in the trans line? Is there a certain voltage I should be seeing?

John Faughn

The temp sensor just makes a connection when it reaches a preset temp [ 40 *F ] .
So using a multi meter to look for open / close at above & below temp , if no change , then bad , what I did was to take a 1,000 ohm resistor and connect the 2 leads going to sensor , so the connection is always there , but this is part of what is used to protect the trans [ do not let it shift into high gear or OD , till temp is reached ] .
As with all the suggestions , use testing to find problem , so save money & only replace what is bad .

Wet1

Can I just place a jumper wire across the two leads (I assume there are only two) going into the sensor?

I tested the TPS last year and it seemed okay. I'd like to bypass this temp sensor and make sure that isn't the problem, and I'd also like to check the connections at the computer as well. After that, I'm pretty much in the dark.

BTW, where exactly is the computer and are the connections easily accessible? Edit: Passanger side of the firewall as stated above...

John Faughn

You missed the part where I said , put a 1,000 ohm resistor between the 2 wires , unless you want to kill your computer .

Wet1

Nope, I didn't miss it. I just didn't understand why you used the resistor... now I know.

I'll check these things this weekend.