Lorin Thwaits

Recently needed to work on a friend's 12 year old minivan that for some reason still runs.  It's ugly, gets crappy mileage, and has 180,000 miles on it, but still went from point A to point B.  That is until last week when putting it in Reverse to back out of the driveway, it started lunging and making grinding sounds!  With it in Park or Neutral, no issue.  But immediately upon putting it in Drive or Reverse, it either killed the engine entirely due to extra load, or a little motion started, coupled with a terribly annoying grinding sound:

After it was warmed up the engine had a better chance of staying running while in gear, and when driving it would rattle and lunge something fierce.

So I jumped right in and started troubleshooting.  It doesn't have a limited slip differential, so I jacked up one side the thing and put it in gear so I could listen closer while it doing its worst.  I was thinking that the horrible grinding sound may be the torque converter since it did this in both first and reverse.  (I figured how could both of those gears go bad at the same exact time?  It must be something else that's common to both.)  While scouring the Internet I found some resources talking about what the four clutches control in the transmission:

In case you're wondering what the difference is between overdrive and overdrive with lockup, at about 50mph the transmission releases a hydraulically-controlled lockup clutch.  A speed sensor knows when to trigger that.

The transmission actually uses its very own computer, mounted in my minivan against the firewall on the passenger side.  At first glance it looks like the engine's brain, but it's actually the transmission's.

It looks like from the chart that second gear requires the 2/4 and UD clutches to be selected, but if you don't have any clutch solenoids engaged then it actually naturally leaves everything to be as if it's in second.  So this forces the four-speed transmission into its “limp“ mode.  Engaging no solenoids can be accomplished by simply pulling the plug to the solenoid pack connector, shown highlighted in this picture:

It has one 8mm bolt holding it in, and it's pretty simple to reach with a 12“ extension.

Once I pulled this, although of course the van had no top end whatsoever, it was at least driveable again.  No more grinding!  It wasn't the torque converter after all.  And both forward and reverse work, incidentally due to the reverse running off a fluid-based clutch, not an electronically controlled one.  Acceleration was not nearly as bad as I feared, and top speed was around 60mph at 4000 RPM.  Fuel consumption at this speed on the guage claimed 15mpg.  Usable, but not great on the freeway.  It has gone 50 miles so far in this mode.

So now I'm of the opinion that the problem is either with the OD clutch itself or with a sensor that fools the transmission controller (TCM) into thinking it should be engaged when really it shouldn't be.

Moral of the story: if you have one of those wretched trouble-prone A604 transmissions found in all the Plymouth, Dodge, and Chrysler vehicles listed below, and you start having transmission trouble, you can put it in its limp mode yourself to at least avoid towing charges, and maybe use it until you can buy another ride!

Other Mopar transmissions such as those found in the Intrepid are very similar and would probably also work the same with this technique.

(You can read about the very simple resolution for this issue in this future post.)