2006 Caravan 345,000 miles.

Ran fine, then suddenly it wouldn't start. Noticed that the shift indicator showed it was in Reverse or any other gear, but never in Park or Neutral. I assume that means the ECU thinks it in a gear and won't allow it to start. I can jump the starter with the key on and it will crank just fine but it won't fire.

We threw a range switch at it and no love there. I have tested the harness from the range switch to the PCM and everything is good there. I even put the harness connector on the old switch and tested through the switch and the connectors to the PCM and all is good.

I have tested the ground for the range switch and that is good.

Where is the ground for the PCM?

What else am I missing? I have found a thread someplace where all of the blocks were lit around all of the indicator letters like we have now but I can't find it anymore...

 

I have the trans harness out and I hooked up the four wire connector that has the ground wires running through it. I then put my test light on the pins at the ECU connector (not the ECU) and the test light came on, verifying that I have a good ground.

What else?

 

Snagin' frazzin' friggle frack.

It works now. WTMFF? I had the harness off and back on and the battery disconnected for longer than I had earlier, so was it a bad connection or was it the switch and it had to reset with the battery cable off?

The big problem is that this hauls people in wheelchairs and breaking down is a bad thing.

Any suggestions on what else may have gone wrong?

 

So, now that it's running, I figured that I would put down what I learned and how I tested it all.

As I have been thinking about this tonight I realized that when the gear indicator moved through the drive gears, it showed where the range selector switch wasn't working. So how does the range selector switch signal what gear you have selected? I was stumped since there are only four wires signalling six different positions, until I really got the wood burning. The switch controls grounds for the PCM, and depending on what combination of grounds, the PCM sees what gear you have selected.

Pin 7 is grounded in N, D and L
Pin 8 is grounded in P, 3 and L
Pin 9 is grounded in P, R, N and L
Pin 10 is grounded in P and N

Put another way:
In P, pins 8, 9, and 10 are grounded
in R, pin 9
in N, pins 7, 9 and 10
in D, pin 7
in 3, pin 8
in L, pins 7, 8 and 9

Now that I have this typed out, I can see that pin 10 circuit must not have been working. Actually, this gives me more confidence that the switch was the problem and I just needed to reset everything.

The range switch was about $50 so it's not expensive, but you need to ball-up to swap it out since you have to drop the trans oil pan and valve body:

Start by disconnecting the shift linkage. It just pulls straight up. Then loosen the bolt on the shift lever where it attaches to the shaft going into the transmission.

Have a drain pan handy and drop the transmission oil pan and filter. Find the 10 MM-headed hex bolts; there are a bunch of them, I didn't count. When you get the last ones out you will get more oil running out so be ready. The valve body will now drop out. The shift shaft comes out with it so you have to wiggle things around a bit to get it to come down.

CAREFUL. This is where the pucker factor increases. There are two accumulator pistons with springs that are held up by the valve body and they WILL fall down when you lower the valve body. I wasn't ready for this so I had to spend some time figuring out what went where since one piston had two springs and one had one spring. What it came down to is that... you know how that grey metal dirt coats stuff in a transmission? I saw where the springs sat on the plate of the valve body and I saw the witness marks of the inner spring in one spot and not the other.

Anyway, you should now have the valve body in a clean work place. Just one torx-headed screw holds the switch in place. Remove it and the switch comes up. There is a seal on the shift shaft and in a perfect world, you would want to replace that seal after you put the new switch in place.

To install the valve body with the accumulator pistons and springs, I cleaned the parts and the bores with brake cleaner and blew them off so they would be dry. I then loded things up with Vaseline brand, pure petroleum jelly and put the accumulators and springs in the bores. I forgot what the torque is on the bolts. Sorry.

Other than that, assembly is the reverse of removal.

The grounds for the PCM run through the four pin connector near the PCM in front of the front, left wheel. It's the black wires, I didn't get the pin numbers. They connect to the battery ground. To test the circuit, I pulled the connector from the PCM and found pins 13 and 14 and - with the four pin connector connected, I used a test light. the clip was one the battery positive and I probed pins 13 and 14 with the pointy end. Since the test light lit up, that showed that the ground was good. I could have used a multimeter to test resistance, but with the test light, that puts a load on the ground circuit so if there is corrosion or something in the circuit, this will show it. A nice, bright light is a good thing - a dim light indicates high resistance.

I'm tired now and maybe I'll think of more information later.

 

I signed up here to say thanks for the run down. My wifes van is a 07 grand caravan sxt with this issue. Last night I went a head and did the trs with my fingers crossed but unfortunately no avail. Pretty sure the old one was dead as it start to show reverse while in park and starting occasionally to all blocks lit up in the shift indicator and no start. Now with new trs shows in reverse and no park or neutral again

Any other ideas? I've left the battery cables disconnected in hopes it will "relearn" or something but over night did nothing. Very frustrating

 

Deez, did you check all of the wiring for the TRS? The battery acid ends up dripping right on top of this area and can eat things up. You can pull most of the wiring harness out very easily. There are just four connectors on the transmission. The TRS that you know about, The output speed sensor just above it, the solenoid connector right next to the trans cooler lines that is held on with an 8MM or 5/16 headed screw then the Input speed sensor right below where the cooler lines go into the trans. Then you can pull that parts of the harness out towards the tire and work on it. The rest of the harness goes to the computer, and you have to pull the bumper to get to that.

I have had ours off three or four times in the past couple of weeks so it's still fresh in my mind and I can walk you through that, but only for a couple more days. I have a Sprinter Transmission to think about now and it's already starting to push out what I did.

 

Thank you sir. I'll be looking into the harness when I get home tonight. What a pita! I'll report back before you lose the info! Thanks again!

 

Thanks again TDI. It ended up being a wire broke on the trs harness. I appreciate the help!

 

I may need a trans harness now. The van did the exact same thing in the exact same parking spot as last time. According to the diagram, I should have been able to start it by jumping pins 8, 9 and 10 to ground, but no love. So either the wiring is bad or the new switch is bad.

 

Well, Sigh...

This van is troublesome these days. I have had the wiring harness off completely (Five minutes, without pulling the bumper, BTW) and opened it up and everything is perfect in there. I put it back together and everything is back to working just fine.

I am very sure that the problem isn't in the wiring and it has a new switch, but I'll have to check that again if it fails again.

The question I have is that if the wiring is good and the switch is good, that leaves the ECU. $650ish plus flashing at the dealer and $150ish from the bone yard, but what would I need to do if I get one from the bone yard? Can that be flashed somehow?