Trans question 42RE vs. 46RE - 99 Dak

3475 Views 15 Replies 6 Participants Last post by donram360, Apr 4, 2021

B757Captain

Discussion Starter · Feb 23, 2021

Hi guys,

Just finishing up my 3.9 to 5.9 swap in my 99 Dakota. All good, easiest swap I've probably ever done except for one little problem. I'm having absolute hell trying to find a 46RE to replace the 42RE that was behind the 3.9. The current trans was/is working fine and I figure I can keep on using it while I continue looking for a replacement. Here's the problem:

I now have no overdrive or TCC lockup. Had it before and I made no changes to the wiring harness other than add for the extra injectors. I had the donor computer reflashed by B&G and according to Dave the PCM will not support the 42RE - he set it up for the 46RE.

To add to my pain I don't have a FSM handy for the 99 - I do have one for a 98 Ram and I have seen some differences in the wiring, though not in the pinouts. So here's my question for any of the transmission experts out there:

The OD and TCC lockup for the 42RE are controlled by the PCM (I've isolated them through to the 8-pin connector on the trans). Is the 46RE OD and TCC controlled differently? Can I re-pin the PCM connector to get the right signals to the 42RE 8-pin connector? Or am I missing something?

Thanks!

1 - 16 of 16 Posts

dandress1133

· #2 · Mar 1, 2021

B757Captain said:
Hi guys,

Just finishing up my 3.9 to 5.9 swap in my 99 Dakota. All good, easiest swap I've probably ever done except for one little problem. I'm having absolute hell trying to find a 46RE to replace the 42RE that was behind the 3.9. The current trans was/is working fine and I figure I can keep on using it while I continue looking for a replacement. Here's the problem:

I now have no overdrive or TCC lockup. Had it before and I made no changes to the wiring harness other than add for the extra injectors. I had the donor computer reflashed by B&G and according to Dave the PCM will not support the 42RE - he set it up for the 46RE.

To add to my pain I don't have a FSM handy for the 99 - I do have one for a 98 Ram and I have seen some differences in the wiring, though not in the pinouts. So here's my question for any of the transmission experts out there:

The OD and TCC lockup for the 42RE are controlled by the PCM (I've isolated them through to the 8-pin connector on the trans). Is the 46RE OD and TCC controlled differently? Can I re-pin the PCM connector to get the right signals to the 42RE 8-pin connector? Or am I missing something?

Thanks!

That whole thing sounded weird.

Sent from my SM-J260A using Tapatalk

B757Captain

Discussion Starter · #3 · Mar 3, 2021

Weird as in I didn't make any sense?

Or the problem makes no sense?

RXT

· #4 · Mar 3, 2021

I'm not a transmission guru, but I have a 47RE that now has a manual valve body. To get OD and LU, I wired a pair of switches for both. I suspect you can do the same with the 42RE to get you by until you can locate a 46RE. Just make sure you don't forget to turn off LU before you come to a stop, otherwise you could stall the engine.

Ed

B757Captain

Discussion Starter · #5 · Mar 3, 2021

I'm trying to stay away from the manual actuation via switches partly because when the problem is finally identified it will probably turn out to be something simple, but also occasionally the wife will be driving the Dakota so guess what she will say about having to remember the drill about manual OD/TCC switches!

B757Captain

Discussion Starter · #6 · Mar 3, 2021

Ok, I did some digging and found some more info - trans experts, PLEASE chime in at any time!

According to various parts websites like Rock Auto, etc., all the electronics (that connect through the case to the wiring harness) such as the solenoid controller (governor pressure, OD, TCC and trans temp), the neutral safety switch and the output speed sensor are the same part numbers for the 42RE, 44RE and 46RE. So I'm thinking that the PCM has no idea what trans it is hooked to. Is this correct?

So if I kept the 42RE and didn't change the wiring harness, why don't I have OD and TCC lockup anymore? I also checked a valid wiring diagram, no pinout differences for any of the trans controls so the harness should be good and the PCM and trans should be talking to each other. My next step I think is gong to be jacking up the rear and simulating driving conditions while checking voltages on the OD and TCC pins to see if the PCM is signaling correctly. Any other ideas?

nwrensch

· #7 · Mar 4, 2021

B757Captain said:
Ok, I did some digging and found some more info - trans experts, PLEASE chime in at any time!

According to various parts websites like Rock Auto, etc., all the electronics (that connect through the case to the wiring harness) such as the solenoid controller (governor pressure, OD, TCC and trans temp), the neutral safety switch and the output speed sensor are the same part numbers for the 42RE, 44RE and 46RE. So I'm thinking that the PCM has no idea what trans it is hooked to. Is this correct?

So if I kept the 42RE and didn't change the wiring harness, why don't I have OD and TCC lockup anymore? I also checked a valid wiring diagram, no pinout differences for any of the trans controls so the harness should be good and the PCM and trans should be talking to each other. My next step I think is gong to be jacking up the rear and simulating driving conditions while checking voltages on the OD and TCC pins to see if the PCM is signaling correctly. Any other ideas?

Hi
You will find this answer kinds weird, but check your alternator. The PCM sends a signal to the alternator to energize the stator, from there the power for there goes to the transmission relay to activate that. I ran into this in my 2000 Durango with a 46re. What happened with mine is the power went to the alternator but the brush that sent the power to the relay was shorted out in the brush holder, changed the brush holder and brushes all is good now for the last 2 years. Take a voltmeter and with the truck running back probe to check and see if you have power at both wires on the two prong plug on the alternator. I had one hell of a time finding that one, Because the alternator was still charging, because the the holder was acting as the ground, instead of the relay being the ground.
Have fun

dandress1133

· #8 · Mar 5, 2021

B757Captain said:
Ok, I did some digging and found some more info - trans experts, PLEASE chime in at any time!

According to various parts websites like Rock Auto, etc., all the electronics (that connect through the case to the wiring harness) such as the solenoid controller (governor pressure, OD, TCC and trans temp), the neutral safety switch and the output speed sensor are the same part numbers for the 42RE, 44RE and 46RE. So I'm thinking that the PCM has no idea what trans it is hooked to. Is this correct?

So if I kept the 42RE and didn't change the wiring harness, why don't I have OD and TCC lockup anymore? I also checked a valid wiring diagram, no pinout differences for any of the trans controls so the harness should be good and the PCM and trans should be talking to each other. My next step I think is gong to be jacking up the rear and simulating driving conditions while checking voltages on the OD and TCC pins to see if the PCM is signaling correctly. Any other ideas?

You need the right pressure solenoid or transducer depending on year like put the 42re sensor and switch in the 46re. The transmission does not talk to the ecm only sends ok or not ok signals you can use a jumper wire instead of relay to trick out of limp.

Sent from my SM-J260A using Tapatalk

dandress1133

· #9 · Mar 5, 2021

dandress1133 said:
You need the right pressure solenoid or transducer depending on year like put the 42re sensor and switch in the 46re. The transmission does not talk to the ecm only sends ok or not ok signals you can use a jumper wire instead of relay to trick out of limp.

Sent from my SM-J260A using Tapatalk

Your gonna ruin that 42 behind a 5.9 need a 46
TV cable all wires plugged in ???? The down stream 02 sensor will make transmission act funny taking of in 2nd not shifting to od cant believe no code you probably dont have the right ecm and I know you didn't program that stock 99

Sent from my SM-J260A using Tapatalk

nwrensch

· #10 · Mar 5, 2021

B757Captain said:
Ok, I did some digging and found some more info - trans experts, PLEASE chime in at any time!

According to various parts websites like Rock Auto, etc., all the electronics (that connect through the case to the wiring harness) such as the solenoid controller (governor pressure, OD, TCC and trans temp), the neutral safety switch and the output speed sensor are the same part numbers for the 42RE, 44RE and 46RE. So I'm thinking that the PCM has no idea what trans it is hooked to. Is this correct?

So if I kept the 42RE and didn't change the wiring harness, why don't I have OD and TCC lockup anymore? I also checked a valid wiring diagram, no pinout differences for any of the trans controls so the harness should be good and the PCM and trans should be talking to each other. My next step I think is gong to be jacking up the rear and simulating driving conditions while checking voltages on the OD and TCC pins to see if the PCM is signaling correctly. Any other ideas?

And I was also sure of the 42re, 44re, and 46re electronics bring the same. I was a transmission tech for many years but got out of it about 20 yrs ago. Did you check the alternator power in and out yet? Check for power to the transmission relay. Just asuming that it is ok because it is charging is does not mean that all is good. I ran into trouble with my caravan because of the same alternator problem's.

B757Captain

Discussion Starter · #11 · Mar 6, 2021

My multi-meter decided to crap out so I had to replace it - I just checked the alternator, I've got power when running at both wires and power in and out of the transmission relay. Working from there will check at the PCM next.

nwrensch

· #12 · Mar 11, 2021

Have you checked to see if you may have pinched a wire between the engine and the bellhousing, grounding it out or even cutting it off. I've seen it happen before.
Norm

B757Captain

Discussion Starter · #13 · Mar 14, 2021

I know that didn't happen, only because the entire harness was out of the truck when I stabbed the engine. I just spent today checking continuity on all the pins/wiring between the 8-pin trans solenoid plug and the PCM. All ok, even wiggled the harness checking for loss of continuity. Next step is I found a guy locally who can plug in his scanner while we motor down the road so he can see if the PCM is talking to the trans. That should point to the next step.

B757Captain

Discussion Starter · #14 · Mar 21, 2021

Update:

I went for a ride with my guy and his scanner. What we found was that he could operate the solenoids and verify (hear) them cycling. Went for a drive with the scanner plugged in - overdrive started working again but no TCC lock-up. He could verify the action after the fact but couldn't verify if the computer was signaling or not. So basically we determined that the PCM was the prime suspect. And as of yesterday - the PCM was it! I found a PCM at a U-pull-it and swapped the computers, trans now functions perfectly.

Now I have another conundrum though - from sleuthing on the interwebs it seems that loss of trans functionality is a fairly common failure point for our PCMs. So did I send a PCM to the tuner that had that pre-existing failure? I sent the PCM to be tuned before first start of the 5.9 so I don't know. If so, did the tuner not catch that the PCM was bad, did he not test it before (or after) the tune, or did he send me back a bad unit and I wasted $400? My thought is that at some point during the tune there should be a test to check all functions, and I doubt that it failed during shipping!

To top it off, the truck runs better with the factory PCM tune! Better hot starting and I was getting some pre-ignition during spirited acceleration, no longer with the stock PCM. That tells me that the tuner's tune was garbage (for a stock setup anyway) and he kicked the timing curves up too aggressively. No way to tell via mileage because I can't compare apples to apples since with the old PCM I was limited to 3rd gear.

So the conundrum is this - the new PCM is from a 99 Dakota with the 5.2. Is there enough of a fuel curve difference between the 5.2 and 5.9 that I will have some lean running problems? I can't discern any drivability issues with lean running but will keep an eye on it. I can live with the CE light on due to VIN discrepancy for the time being, so do I really need to send this new PCM off for a reflash or not? For now I plan on leaving it as is so I can enjoy the truck.

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Dads last truck

· #15 · Apr 2, 2021

Glad you figured it out.

donram360

· #16 · Apr 4, 2021

The computer don't know what engine it is running. It uses inputs for things like temp and o2 in the exhaust (thee are others I know but don't need to detail every one of them, to make the point) as long as it is a V8 computer and there are sensors to satisfy each thing that the computer looks for it won't care if it is really a 318 or a 360.

I have a 01 Durango with a 360. Had a computer issue that drove me crazy, I was wanting to swap out the injection for a carburetor. I went to a junkyard and got a computer from another 01 Durango with the 360. It would start and quit. Start and quit. Start and quit. It would run for a few seconds but die before I could release the key. Damned security.
I had previously sent the original computer on for repair. Twice. And then this. So finally I had to send the junkyard computer in to be reprogrammed with my VIN for it to run. Wait some more.
They did that and fixed the original (finally) and claimed the tech that worked on it originally "didn't work there any more" that was why it took 3x to get the original one right. (I guess they canned e guy, had other problems with his work) supposedly.

My original problem was a #6 misfire reported by the computer that didn't exist. I guess there is a chip that likes to lose its solder bond in there, pretty common according to the computer repair place. Then I got it back and worked fine for a week then had other issues. Then had it stick 2 injectors wide open and wash the cylinders out, ruined a fresh overhaul.
17k later the junkyard computer is and has been alright. I haven't tried the original one back in there yet. At least the 3rd time I sent the original one in and sent the junkyard one along with it I told them that I just needed 1 good unit so my Durango would run. And that all I wanted with the junkyard computer was to redo the VIN so it would agree to run my engine. No more was to happen to that one. They did that, and opened my original one again, sent them both back no charge. But they hole sawed both units and silicones the hole sawed piece back into both. Don't seem that professional to me.

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