Hello, I just installed motor/trans and wired everything up, then checked the scanner and it always says I am always in "D4" and has "reverse inhibited". I think this is because I follow LT1swap.com wiring and removed the wires from the PRDNL (I left the 4-wire plug alone, and the 1 ground on the big plug as well), which may have been a mistake.
Will it hurt to run the trans like this? What will happen when I put the shifter into Reverse? or 1st?
This is what I followed:
So I think this is wrong. Now the trans has no clue what gear I am in of course. What the #@(*@) was I thinking....
So here is what "brandon" from lt1swap.com says,
"It will work fine. That signal is only used for IDLE control..."
"...Those wires are what the computer reads to determine shifter position. 4 signal wires on the small plug, 1 ground wire. What you have on the scan tool I have no idea. Reverse Inhibited sounds like a PID on a LS1 manual trans car. "
So 4 signal wires on the small plug tell the computer shifter position? Then why does my scan tool never change from D4 position. I will have to experiment more and get back.
Last edited by kingtal0n; 04-17-2017 at 02:52 PM.
Alright, so here is what I've discovered so far.
First, I replaced the neutral/park switch (the entire black box on the side of the trans) with a brand new unit from rockauto.
Then I plugged everything in and started the engine.
It worked perfect, for about 30 seconds. I had every gear showing properly, EVERY gear. I was like, yay problem solved.
Then, suddenly, it started flipping out. It would stick in D2, then jump to D4, then to neutral, suddenly without any input from me.
I shut the engine off. Let it rest an hour (I went to get some food because I hadn't eaten all day) and came back, tried again.
Same thing. Works fine for 40~ seconds, then flips out.
I am going to the junkyard tomorrow and pulling a used unit off a 4l60e, along with some new plugs/wires. I am sure this will be an easy fix.
And if anyone is curious, it still doesn't shift out of D4 when the engine is off. For whatever reason, it only works when the engine is running. Which is fine with me... if only it would keep working!
Today I installed the next unit (P/N safety switch, the big black box on the side of the trans) from the junkyard. The big plug seemed GLUED into it, so I left it inside (I tried removing the big plug from several others in the JY and broke them all). Very strange, that.
Anyways, Leaving the big plug in it, I wired the single black/white wire (the ground) to the harness, and plugged in my 4-wire brown plug. Then I started the car. This time, It only showed me park, then D4, then park, the D4, then park, then D4, every click down on the shifter was either Park, or D4, and it would alternate between them. I started thinking the ECU was messed up, or the ground is somehow weak or wrong (could be possible as I have not yet finalized the harness for my swap, it only has 1 major ground to the battery)
So, thinking everything was still screwed up, I put the car away. Then, I restarted it after a bit, and suddenly it started working perfect. And kept working perfect. I don't know why it suddenly started working perfect, but I had to shut it off for the day and left it wondering why. I will continue to investigate. Either the computer is messed up, or the ground is terrible, are my two big guesses. I think the switch itself is fine.... and now that I think about it, the switch has an adjustment, the slotted holes on the sides of the trans can move it back and forth. Maybe it just needs an adjustment (might be hanging "between" gears or something) So that is something else to try.
Alright well, I solved this today. sigh, my fault completely. But before you go shaking your head at me- you gota understand one thing. As a programmer, I have a fair understanding of how computers think, just in general. So when the transmission sometimes shows me "working fine" (park, reverse, neutral, D4, D3, D2, D1) and sometimes shows me "Park, D4, park, D4, Park, D4, Park, D4" I think to myself, "well thats odd,..." And I check the logic for the controller and find out that to go from Park to D4 its a complete reversal of the low/high at the neutral switch (all lows go high, and visa versa) which led me to believe two things. The first was that, in order to completely swap all "lo" for "high", and not just have some random output occur, that is a very specific behavior. In other words, what I was seeing wasn't random. A random malfunction or ground issue would have it flopping around randomly, I wouldn't get park then D4, then park again, the D4 again, perfectly like that. The second behavior I noted, and this is what really threw me off the trail cold, was the fact that sometimes it worked fine, and other times it didn't. In fact, with the brand new neutral switch it worked perfect for about 30 seconds. That was really, really strange to me, and I absently ruled out any programming in the software since it looked like it was working fine at least for a moment, which meant to me that at least the software knew what it was looking for when it saw it.
Yeah so, long story short, it was the software programming after all. I don't know how it is possible for the programming to be wrong, and still get a working switch for 30 seconds, or for any length of time, but it is. In the software there is a setting which asks if you have "just park and neutral" or "PRNDL" or "NONE" and I had it set to "just park and neutral". I switched it to "PRNDL" and now it works fine, all the time, even when the engine is off. So call me $@(#*&$@ but thats all it was. And I don't know the relationship between different switches either, but apparently you get a different behavior depending on the switch itself. For example, the original neutral switch gave me "stuck in D4 all the time". Whereas, The brand new neutral switch gave me "working perfect for 30 seconds then erratic behavior, sticking to D2 then jumping to D4 etc...", and finally the next, used neutral switch from a junkyard truck gave me "park, D4, park, D4, park, D4," through each gear. So yeah, very strange considering they all output the same logic.
Last edited by kingtal0n; 04-26-2017 at 01:29 AM.
Can you share where the changed in HP are located for the PRNDL? I've looked and cannot find them. I get P, R, N, D6, D4, D1, D1, D2.
The black box on the side of the trans is a park neutral position switch. It's entire job is to tell the PRNDL on the dash what to do, back up lights and tell the computer when it's ok to run the starter (PN). The PCM/TCM get's it's gear info from the position switch in the valve body, not the PNP switch.
Hmm. I've got a 6L90 swapped into my 78 Blazer so I was trying to figure out why as I shifted down through the gears it would do that. Is it possible my Position switch in the valve body isn't right? I took it out of a truck that only had PRDM so didn't know if it would know what to do or if I could make changes so I could get it to be PRND4321
6lxx is PRNDM maybe PRNDM21 in some rigs. Could even be PRND M/S, if it has sport mode. But definitely not PRND654321 or whatever.Originally Posted by Phillipm
Roger that. Just wanted to confirm there wasn't a way to do it. I'll put my mind to better use elsewhere! Thanks for the help.
I might be late to the game but let me add some helpful information. On the 4L60E, and 4L80E NEUTRAL safety switches/MLPS that have TWO connectors-YES, they really are glued in!!!!! You MUST heat them up with a heat gun, or small butane/propane torch before trying to unplug them. Once you get them hot, the connectors will come right out without issue. If you try to pull them out cold YES, you will either break the actual shroud around the connector, or pull the wires/pins loose from inside the on-body-harness connector. You must ALWAYS heat the connectors before removing them, and/or installing them. You read that right-you must heat the glue inside the switch when going to install the connectors back into them. The later style switches that utilize only 1 connector DO NOT require this as they have no glue inside them.
I know someone will come along and say "I've never had to heat them up before".. To that I say, try it the CORRECT way and you'll love how much easier this task becomes. You also won't be breaking switches. The other thing I'd like to add is that when removing the switches from the shift shaft lever, the switch should slide right on, or off, without any resistance. If the switch hangs up on the shaft while trying to remove it, or install it, STOP! Take a small file and file the sharp edges off of the shift shaft lever where the factory stamped the flats onto the shaft. Once you get it filed enough the N/switch/MLPS will slide right on/off without any resistance. If you don't file it and you force the switch on/off, you run the risk of damaging the switch internally. You won't be able to see this damage, but you'll know when the vehicle does not start, or fails to start intermittently, or does not register the correct gear on the dash, or on a scanner. There is no sense in man-handling the switch, or the connectors when a little finesse is all it takes. This is an area where working smarter can save you both time & $$.
I went through a similar experience. When I first had PRNDL issues I went to grab another neutral switch from the junkyard, seemed logical to carry a few spares.
After I destroyed two of them trying to get the plugs out, I realized I would need a better plan. Instead, I cut the wires and left the plugs in the neutral switch. Then wired those, 7? wires into the trans harness and the plugs can just stay put right where they are nestled.
I have an older unit in my car that didnt come with the PRNDL box. My trans always reads first gear but im sure i habe PN switch or should.
Should i change my settings to PN so the car knows what gear its in. I get some issies when switching from gear to park or nuetral
1997 30th SS. Torqhead 24x, TFS heads, 223/235 cam, 4l80e, S60 D1SC 14psi
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