I recently was assigned to try to diagnose a '98 Ford F150 that would not shift into overdrive. The first 3 gears were fine, but when the upshift to 4th happened, the transmission went into a freewheeling mode, Mexican overdrive (very appropriate because it is in New Mexico),. A scanner in data mode shows that the 2 shift solenoids are not in the correct state for 4th, but the scanner shows that the tranny is in 4th gear. I am beginning to suspect the Powertrain Control Module, but I don’t have enough experience with automatics to be sure of myself. Can anyone help me diagnose this problem? What should I do next?
And there are no actual error codes present? There is a real trans tech who visits on occasion and he can give you specific guidance if he stops by. But in the meantime, its seems to me that this says the PCM intends for it to be in 4th - it is commanding it - but that the solenoids themselves or their power supplies are not doing their job. But at that point the PCM should “see” that it commanded 4th, but that the engine & transmission action don’t indicate 4th. That should set an error code. If there aren’t any codes, that would be weird.
Thanks for the input. I neglected to mention that when I did a Key On Engine Running test, an error code was set that indicated the engine didn’t slow down when the transmission went into 2nd gear. I think the error code was P0475 or thereabouts. In spite of that code there is no Check Engine light on the dashboard display.
I spoke to a transmission tech on Friday and got his opinion that the loss of overdrive was the first symptom of declining health for the transmission. He thinks it will eventually fail completely, but maybe not for a while. Even if the PCM is the culprit, he says it would cost about $1K to get another one just to check it out… Maybe not worth it for an old truck.
That’s what drives me nuts about many transmission techs - and other mechanics in general - when it comes to transmission troubles. The only thing you often get out of them is whether or not they think the transmission is failing, and they take any kind of issue to indicate that the whole transmission is failing.
Ok - fine. Well, there are normally several reasons that a transmission will or won’t do X (like go into its overdrive gear). It can be an electrical issue having to do, for instance, with solenoid function - solenoids themselves or wiring for them. It can be a pressure problem also either from solenoids or from internal leaks. Or it can be mechanical - e.g. the 4th clutches could just be gone.
In your case, you basically said the PCM is commanding 4th but the solenoids apparently aren’t getting the message. If our “real” trans tech comes by he can tell you smarter things than I, but I would get the trans up to temp and check the resistance on the relevant solenoids. I would also get a pinout for the transmission connector, pull the wiring harness to the trans, and inspect. Inspect the wires that supply those solenoids & check for corrosion or other issues with the connector pins.
I would not assume, however, that a couple of solenoids that aren’t in the correct state for engaging 4th mean that the entire trans is about to kick the bucket. If you said the PCM commands 4th and the solenoids are in the correct state, but 4th doesn’t engage then I’d tell you that the trans is probably done for & in need of a rebuild.
How many miles are on it? What has its service history been (fluid/filter)?
What are the solenoids showing in 3rd and when 4th is commanded?? I also need to know which transmission you have. Its either going to be a 4R100 or a 4R70W. The 98 F-150 comes with both. To tell the difference count the pan bolts, the 4R100 has 20 pan bolts and the 4R70W has 14. These are two different transmissions.
In response to transman618, the pan has 14 bolts and as I remember it the solenoids were showing the correct states when the transmission showed 3rd gear, but in 4th, they should have both been in the OFF state, but one was ON. I haven’t had a chance to put the scanner on the truck lately so I can’t verify this information. As things stand now, the truck is being used on a project that only requires low speed operation and I have requested the drivers to switch OFF overdrive. We’ll see how long it lasts in that mode.
Regarding the questions left by cigroller: I changed the transmission filter a couple of weeks ago when the truck had 110K miles on it. The fluid was a little dirty, but didn’t smell burnt. The donut shaped magnet was covered with a thick layer of fuzz, but no big chunks. As far as I know, that was the first filter change for this particular truck.
If you’re lucky transman will return to the thread.
My googling tells me that for 4th both shift solenoids are on rather than off:
(1-2) / (2-3)
1st: on / off
2nd: off / off
3rd: off / on
4th: on / on
When you have it again put it back on the scanner and just write down what you have in each gear & post the specifics. I could guess some more. Or if transman stops by he can tell you more intelligent things. There are also a couple of other characters around who know a thing or two about auto trans.
Also get a better description of “freewheeling mode.” Is it basically acting like its in neutral? Or is there heavy engine braking (as if it did a massive downshift).