So today I went and got my 98 4.0 4x4 auto smogged(California ☹️) and it passed with flying colors! I was smiling almost the whole way home! Until I hit traffic on the highway and had to come to a stop. When I tried to accelerate, I was hearing some grinding and it seemed like it would not go into first. It would then shift up and I could get going very slowly. It also started to sound like it was grinding when it is changing gears. And then a few moments later I got the check engine light. I was able to nurse it home, but when taking off it always felt like it couldn’t go into first, grinding into other gears, and at high speeds it sounded like the u joints were going bad and vibrating (just changed all of them a few months ago because of Highway vibrations. Drove very smooth afterwards until today ) I am going to drain the fluid tomorrow and check for metal shavings, but I fear I will need a new trans…

the only reason I think I may not is that I can put it in 1-2 and it will catch, then shift into 3rd and drive. It still felt like it was grinding a bit but it was better. Do you think it’s as simple as Shift solenoid? Or will I need a new trans?

The fluid in it was only a few months old dex/merc III. The only code I got was the generic P0700.

 

It sounds like failing #1 solenoid to me, since putting the shifter in (1-2) gets it into 1st gear. Grinding and shaking doesn't sound like the trans as there are no gears that "engage" when shifting like manual transmission. It's just clutches engaging. The AW4 is a pretty robust transmission and mechanical failures are rare.

 

Wouldn’t there be more codes that show up if it’s the solenoid? I find it odd that it only gave me the generic P0700 code

 

Because transmission codes are vague on these. I did a manual swap and got p0700 and a couple others. I put resistors in to simulate the solenoids and I still got a p0700. I put the range sensor back on and it went away. I took the range sensor off one day and it never came back.

I'm curious to what this grinding noise is. Maybe it's the solenoid losing continuity and it's making a buzzing sound? Sorta like a starter on a weak battery? I'd definitely go hand over hand with the wiring from the big connector by the dipstick down to the transmission.

 

Only gears i can think of in the trans are the planetaries. But i dont know enough about them to diagnose it. If its not the trans, then the transfer case may be partially stuck between modes for whatever reason, if you have 4wd. Again, i dont know.

 

So I replaced the solenoids and there was no change.. thinking it may be an internal problem. The grinding ended up being something else.

So my problem is that it seems like it is missing second gear (originally thought it was first) And the only code I’m getting is P0700. Any other suggestions?

 

How's the fluid look? Have you ever dropped your pan?

There are a few sensors that can affect shifting issues. If the transmission is completely skipping a gear, it might be a sticking valve in the valve body, or it could be an issue with the TPS (usually causes shifting too late or too early), an input, or output speed sensor issue.