Everything you ever wanted to know about the AW4

[memasmuffn]

OK. i know this is in reference to a very old post...but a very valuable post!
My problem was with the difference between the 96-97-98 aw4...The vehicle I purchased was a 98 with a CEL code of P702 ...Hey no problem right? just a 02 sensor...WRONG! seems that someone replaced the 98 aw4 with a 96 aw4..After hours of research I stumbled across this great post and it made me understand what I was up against. --(transmission) 1996 1 output sensor(1pps reed),--- 97 change in wire harness, ---(vehicle) 1998 1 input and 1 output sensor(2 wire 4 pulse)both the same part # but different from the 96 and 97---- I live in an emissions area
and need that code gone...lawsoncl had posted a what if in a reply post about a 97 TCU fooling the ECM...I figured that someone had already spliced the harness connectors so why not give it a try...after finding wiring diagrams for both the 98 and 97 TCU, and finding that they were wired the exact same minus the input sensor on the 97, i sat out to find the 97 TCU...brought it home ,plugged it in,CEL code is gone,gone,gone!!!arty:I am very,very happy because now I can continue my build without dropping another tranny into a perfectly running beast.
This fix also means that almost any aw4 can swap into almost any cherokee..Right?

 

[kastein]

NICE!!!

I am glad you posted that up, I hadn't found a 97 TCU to try this with yet. I'll add it to the OP as another method to use!

And yes, that makes it so basically any AW4 can be used in any XJ with the appropriate sensor, TCU, and/or tail rotor swapping. 98 and later into 97 and earlier by swapping the tail housing, rotor, and sensor is easy hard-part wise, 97 and earlier AW4 into 98 and later XJ was the only truly difficult swap and you've just proven it can be done simply by swapping the TCU. :cheers:

Can you thrash on it for a few weeks, make sure the codes stay gone, and post up again? I thought I licked the issue a while ago in my testing but the code came back when I least expected it, so I'm always a little skeptical until it survives the test of time now. Either way, it's going in the OP until further notice!

 

[memasmuffn]

Its been 2 weeks and about 250 mi. I've been in the same situation where I thought I had something licked only to have it rear its ugly head again...Thank you again and I hope this helps someone else.

 

[lawsoncl]

...lawsoncl had posted a what if in a reply post about a 97 TCU fooling the ECM...I figured that someone had already spliced the harness connectors so why not give it a try..

Wow, people actually read my ramblings! Nice to hear that my speculation that an OBDII 97 TCU might play nice with a 98+ ECU turned out to be true. Yet another option for swapping.

So it plugged right in and you didn't have to modify the connector then? On some of the older TCUs the different colored connectors were 'keyed' slightly different, but you could fix that with an exacto knife.

 

[OntheOffRoad]

So just did a swap (engine and Tranny/Tcase)
Donor: 1992 4wd, NP242
Recipient: 1997 2wd

Some comments:
This thread has a ton of vital information in it, read it and learn. It was AWESOME to find it. Thanks to all who have contributed, very much appreciated.

There are a couple points that were touchy for us as we did this, being new to the transmission/connections, somethings were not obvious.

1) NSS - Neutral Safety Switch is barely mentioned.
This is the "other" connection from the trans the cable harness near the firewall. It too did not match (along with the 5 wires that needed to be spliced). I spent hours trying to find out what to do about the NSS.
It was so simple that in hind sight anyone who knows about them would not even think twice about what needs to be done. But for the new idiot holding the wrench, a mystery of frustration.
Simply remove the NSS from teh old transmission and put it on the new (for me take the 97 NSS from the 2wd and pop it onto the side of the 92 trans so the cable just plugs in).

2) Vehicle speed sensor(s) - There are two.
The writeups talk alot about the speed sensor, also much about the output shaft conversion of a 2wd. But nothing that details the information about the 'second' VSS connection that helped us out. The 1997 has a three wire VSS on the end of the trans at the output shaft, while the 1992 has a two wire VSS in the transfer case. Both had the first and more commonly discussed hall effect sensor on the top of the trans near the tail end, which matched and were connected to the 5 pins to be spliced. The other two sensors don't look the same at all and have a separate harness that connects up either near the O2 sensor (97 2wd) or the firewall (92 4wd). The first one is a pulsed hall effect sensor that creates pulses off the lobs mounted to the tailshaft, lots of information on this sensor. The other is gear driven off the output shaft mounted on the end of the trans on the 97 2wd or mounted to the tcase on the 92 4wd. Not much written up on the gear driven sensor or the conversion of the two to three wire connection. Finally I just pulled them both and found that they appear to be interchangeable. Haven't driven the vehicle yet, so don't know. The sensor is driven by gears and is the one you swap when you change ratios in your axles to make the speedo read correctly. This will be an off roader, so its not important the MPH reads right.

Lastly the CPS connector were different too. Both two wire, but a different style plug was used. Just swapped these out since the CPS mount on the bellhousing is the same.

Had to pull the consoles from both to get the tcase linkage. Of course the bezel is a different size between the years, so will have to PnP the right size bezel, then swap the number plate (if we can't find one from an NP242).

Hope this little tidbit helps someone in need of just a little more info.

 

[kastein]

My apologies on not mentioning the NSS, it indeed didn't even occur to me.

As for the speed sensors -
98 and later there is an ISS (input speed sensor)
all years have an OSS (output speed sensor) which is at the output of the transmission. 97 and down it's reed switch 1pps, 98 and later it's VR/coil pickup 4pps.
All years (except RENIX) have a VSS (vehicle speed sensor.) It is mounted in the tailcone of a 2wd trans or the tailcone of the transfer case. As you suspect, it just bolts right into the transfer case after taking it out of the transmission while doing a 2wd->4wd conversion. I didn't even think to mention that because most of my knowledge applies to 4x4 vehicles. Make sure you clock the housing properly to engage the gear teeth to the right depth for the number of teeth on your speedo pinion, or it'll strip the teeth off the first time you drive it. New gears are $35 on quadratec so that's more of an annoyance than anything else.

Yes, 91 and 92 (and possibly 93, though I've found that to not be the case) use a 2 wire reed switch style VSS. 93/94 and later use a 3 wire hall effect VSS. Both produce 8 pulses per revolution of the speedo gear. I didn't really mention much about them in this writeup because they aren't actually related to the transmission controls, just the ECU and instrument panel.

 

[Ecomike]

On the Renix, 87-90, AW4 they used an old style speedometer cable at the AW4, it connected to a VSS hidden behind the dash-gauge assy, and the VVS data went to one of the computers, ECU or TCU, IIRC. Which one, I don't recall, or just have not had to figure out yet,:laugh3: LOL.

Which reminds me, it is one of the few parts I still do not have a spare for

 

[kastein]

AFAIK that VSS behind the dash is only for the cruise control on RENIX. I know that's how it is on YJs of that era, and the color codes and cruise control harness + computer are standalone and very similar on XJs.

I know there are different speedo cable assemblies listed for cruise and noncruise RENIX... that figures into that.

 

[Ecomike]

AFAIK that VSS behind the dash is only for the cruise control on RENIX. I know that's how it is on YJs of that era, and the color codes and cruise control harness + computer are standalone and very similar on XJs.

I know there are different speedo cable assemblies listed for cruise and noncruise RENIX... that figures into that.

That may be why I forgot which computer it connects to, LOL. I have cruise on all 3, and NONE of them work, LOL. Never have really tried to debug them either. So the Renix / AW4 combo, ECU and TCU managed with out a VSS, very interesting!!

So how does the TCU know which gear the AW4 is actually in to decide when to lock up the TC if it has no VSS input?

Or is the TC lock up also a hydraulic circuit, with an electric override from the brake light signal?

My 87 initially locks up in third at about 35 mph, but waits till it is at 1200 rpm and 25 mph to unlock even with the brake applied.

 

[kastein]

On RENIX, the TCU just assumes the trans is in the gear it asked for via the solenoids. No checking AFAIK.

TC lockup is electronic and again it just assumes whatever it did, is happening.

 

[Ecomike]

"TCU just assumes the trans is in the gear it asked for via the solenoids"

Makes a lot of sense for that era!! It used the KISS principle!!!

Thanks, I think I learned a little more renix stuff here today.:cheers:

 

[Ecomike]

I was right, there is more to the Renix VSS story, I think. Under my 2WD AW4, 89 right now, and it has a speedometer cable and another sensor that looks like a VSS mounted to the tail cone. A third connection just in front of the tail cone which I suspect goes to the electric solenoid valves, all on the driver's side. Not including the NSS on the passenger side. I will post up more later. I am pulling the AW4 tail cone to replace the bushing and rear seal for the drive shaft. I may need o'rings for the sensor and speedometer cable connections, and the transmission parts people did not have them so I may need help there????

On RENIX, the TCU just assumes the trans is in the gear it asked for via the solenoids. No checking AFAIK.

TC lockup is electronic and again it just assumes whatever it did, is happening.

 

[kastein]

No, what you described just now is exactly what I described. The "sensor that looks like a VSS" is probably the OSS, that's right about where it should be. The VSS I'm talking about for cruise is up behind the instrument cluster on the speedo cable, maybe 6" back from where it plugs into the back of the speedometer.

 

[Ecomike]

My apologies on not mentioning the NSS, it indeed didn't even occur to me.

As for the speed sensors -
98 and later there is an ISS (input speed sensor)
all years have an OSS (output speed sensor) which is at the output of the transmission. 97 and down it's reed switch 1pps, 98 and later it's VR/coil pickup 4pps.
All years (except RENIX) have a VSS (vehicle speed sensor.) It is mounted in the tailcone of a 2wd trans or the tailcone of the transfer case. As you suspect, it just bolts right into the transfer case after taking it out of the transmission while doing a 2wd->4wd conversion. I didn't even think to mention that because most of my knowledge applies to 4x4 vehicles. Make sure you clock the housing properly to engage the gear teeth to the right depth for the number of teeth on your speedo pinion, or it'll strip the teeth off the first time you drive it. New gears are $35 on quadratec so that's more of an annoyance than anything else.

Yes, 91 and 92 (and possibly 93, though I've found that to not be the case) use a 2 wire reed switch style VSS. 93/94 and later use a 3 wire hall effect VSS. Both produce 8 pulses per revolution of the speedo gear. I didn't really mention much about them in this writeup because they aren't actually related to the transmission controls, just the ECU and instrument panel.

I am totally lost know. I thought you were saying the Renix had no VSS or OSS whatsoever, (OSS or what ever you want to call it???) that talked to any of the Renix computers (meaning ECU or TCU for the moment) in our last discussion, when I asked how the ECU/TCU system knew the vehicle speed on Renix (Outside of the cruise control topic) if that mechanical to electric converter behind the dash was only there for cruise, I thought you said Renix assumed the AW4 was in the proper gear, at the right vehicle speed and had no VSS to verify it, and now I find one I think, and we get tangled up over its name??? So I got the impression it had NOTHING!!! Now I read down lower and I think I see contradictory statements, that may be difference in the name of the part? Or maybe not?

First off, what is the real difference if any, between a VSS and OSS? What am I missing here? Keep in mind my world is Renix, 87-89, so I need to understand it first before you confuse me further with later years, :laugh3:LOL.

Fundamentally isn't a VSS supplying equivalent data to the data an OSS supplies? On the Renix are they not both looking at the output shaft speed of the driveshaft or something equivalent to that and thus both intrinsically seeing output shaft speed which translates roughly to vehicle speed (unless you use non standard tires)? In other words is the name difference a part convenience only or something more complex that I missing?

Lastly, Does any one stock the orings for the AW4 connection for the speedo cable and the soon to be properly named :laugh3: other sensor on the tail cone of my 89 - 2WD - AW4 JEEP?:cheers:

Besides a dealer? (Not even sure they have them??)

 

[Ecomike]

In Post #209, I said

So the Renix / AW4 combo, ECU and TCU managed with out a VSS, very interesting!!

I forgot there was another sensor on the transmission. Getting old sucks....

And your answer to that entire post only mentioned the TCU, and not the ECU, but had me thinking that you were implying both, that Renix had NO speed sensor of any kind for the ECU or TCU. That is where I got lost. I am still wondering about this sensor name game, and is the OSS reporting apx vehicle speed (which is why I was calling it a VSS) as an OSS to the Renix ECU?

Do you see how it is easy to miss read your post below (out of context, skimming) where it says Renix has no VSS!!!!!

As a process engineer (versus being a part naming guru, LOL) I think of them both as a VSS.

I have never had to replace any of them, so it is easy to confuse me with the name variations.:laugh3:

 

[kastein]

AFAIK that VSS behind the dash is only for the cruise control on RENIX. I know that's how it is on YJs of that era, and the color codes and cruise control harness + computer are standalone and very similar on XJs.

I know there are different speedo cable assemblies listed for cruise and noncruise RENIX... that figures into that.

I am totally lost know. I thought you were saying the Renix had no VSS or OSS whatsoever, (OSS or what ever you want to call it???) that talked to any of the Renix computers (meaning ECU or TCU for the moment) in our last discussion, when I asked how the ECU/TCU system knew the vehicle speed on Renix (Outside of the cruise control topic) if that mechanical to electric converter behind the dash was only there for cruise, I thought you said Renix assumed the AW4 was in the proper gear, at the right vehicle speed and had no VSS to verify it, and now I find one I think, and we get tangled up over its name??? So I got the impression it had NOTHING!!! Now I read down lower and I think I see contradictory statements, that may be difference in the name of the part? Or maybe not?

First off, what is the real difference if any, between a VSS and OSS? What am I missing here? Keep in mind my world is Renix, 87-89, so I need to understand it first before you confuse me further with later years, :laugh3:LOL.

Fundamentally isn't a VSS supplying equivalent data to the data an OSS supplies? On the Renix are they not both looking at the output shaft speed of the driveshaft or something equivalent to that and thus both intrinsically seeing output shaft speed which translates roughly to vehicle speed (unless you use non standard tires)? In other words is the name difference a part convenience only or something more complex that I missing?

Lastly, Does any one stock the orings for the AW4 connection for the speedo cable and the soon to be properly named :laugh3: other sensor on the tail cone of my 89 - 2WD - AW4 JEEP?:cheers:

Besides a dealer? (Not even sure they have them??)

In Post #209, I said I forgot there was another sensor on the transmission. Getting old sucks....

And your answer to that entire post only mentioned the TCU, and not the ECU, but had me thinking that you were implying both, that Renix had NO speed sensor of any kind for the ECU or TCU. That is where I got lost. I am still wondering about this sensor name game, and is the OSS reporting apx vehicle speed (which is why I was calling it a VSS) as an OSS to the Renix ECU?

Do you see how it is easy to miss read your post below (out of context, skimming) where it says Renix has no VSS!!!!!

As a process engineer (versus being a part naming guru, LOL) I think of them both as a VSS.

I have never had to replace any of them, so it is easy to confuse me with the name variations.:laugh3:

I have no idea how you are getting this all confused, because I've laid it out pretty clearly, but:
ISS = international space station. Also, input speed sensor. Measures the speed of the input shaft of the transmission, right after the torque converter. 98 and later only. Used only by the transmission controller.
OSS = output speed sensor. Measures the speed of the output shaft of the transmission. Used only by the transmission controller. RPMs measured do not take into account whether the transfer case is in low or high range, since that's past the transmission.
VSS = vehicle speed sensor. On RENIX, only present on cruise control equipped vehicles, installed on the speedo cable right behind the instrument cluster, only feeds the cruise control controller, which is a primitive analog computer on every RENIX jeep I've pulled apart. On RENIX, it is an 8 pulse per revolution (of the speedo gear, not the driveshaft) VR/coil pickup sensor. On 91-92, a reed switch that pulses 8 times per speedo gear revolution. On 93 and later, a hall effect sensor that pulses 8 times per speedo gear revolution. The speedo drive is calibrated using different tooth count pinion gears to result in 1000 revolutions per mile driven, giving 8000 pulses from the VSS (no matter what kind or what it sends its signal to) per mile driven. On 91 and later, the VSS only signals the ECU, which then processes the signal and feeds it to the instrument cluster and also performs cruise control operations based on it. This sensor measures actual vehicle speed whether in low range or not. On 2wd, it's mounted in the transmission tailcone right near the OSS, because there's no transfer case to mount it in.

Clear now? The VSS has absolutely nothing to do with the trans control system, which is why I did not mention it in the original writeup.

 

[Ecomike]

I have no idea how you are getting this all confused, because I've laid it out pretty clearly, but:
ISS = international space station. Also, input speed sensor. Measures the speed of the input shaft of the transmission, right after the torque converter. 98 and later only. Used only by the transmission controller.

OSS = output speed sensor. Measures the speed of the output shaft of the transmission. Used only by the transmission controller. RPMs measured do not take into account whether the transfer case is in low or high range, since that's past the transmission.
VSS = vehicle speed sensor. On RENIX, only present on cruise control equipped vehicles, installed on the speedo cable right behind the instrument cluster, only feeds the cruise control controller, which is a primitive analog computer on every RENIX jeep I've pulled apart. On RENIX, it is an 8 pulse per revolution (of the speedo gear, not the driveshaft) VR/coil pickup sensor. On 91-92, a reed switch that pulses 8 times per speedo gear revolution. On 93 and later, a hall effect sensor that pulses 8 times per speedo gear revolution. The speedo drive is calibrated using different tooth count pinion gears to result in 1000 revolutions per mile driven, giving 8000 pulses from the VSS (no matter what kind or what it sends its signal to) per mile driven. On 91 and later, the VSS only signals the ECU, which then processes the signal and feeds it to the instrument cluster and also performs cruise control operations based on it. This sensor measures actual vehicle speed whether in low range or not. On 2wd, it's mounted in the transmission tailcone right near the OSS, because there's no transfer case to mount it in.

Clear now? The VSS has absolutely nothing to do with the trans control system, which is why I did not mention it in the original writeup.



.......On RENIX, the TCU just assumes the trans is in the gear it asked for via the solenoids.....

Ecomike: So how does the TCU know which gear the AW4 is actually in to decide when to lock up the TC if it has no VSS input?

Your reply: On RENIX, the TCU just assumes the trans is in the gear it asked for via the solenoids

Once again, I am talking about a 1989, TWO WHEEL DRIVE RENIX JEEP!!!! Not a 4 WD, not 92, 96 98 or any other year. MY contention is that the Renix 2WD 1989 sensor on the AW4 in front of the speedometer cable (I guess it is called an OSS instead of a VSS?) is in fact, in reality just another VSS on the two wheel drive rigs, because there is NO TRANSFER case!

What is still not clear is what that speed sensor (OSS?) in the tail cone reports to, the ECU or the TCU in the 1989 Renix 2WD jeep? What happens if I toss it in the trash? LOL What is using that data and what is it doing with that data?

This all started when I asked "If the VSS behind the dash is only used by Cruise, then how does the Renix ECU/TCU know what the vehicle speed is, know what gear it is in????, etc...

But you are getting defensive, and missing my question.

So I give up.

 

[kastein]

I am getting defensive because you just asked a question I literally answered in the post you quoted. You're asking more questions based on unrelated info, and your assertion that the OSS is just another VSS. Yes, technically it is, but they feed different systems, as I said, the OSS feeds the TCU, the VSS only feeds the cruise on RENIX, this is at least the third time I've said this, they have different names to differentiate between them.

The RENIX TCU knows what the trans output speed is because of the OSS. It doesn't care what the vehicle speed is, it doesn't need to know that to know when it's going to need to shift. It assumes it is in whatever gear it told the trans to be in.

 

[Ecomike]

I am getting defensive because you just asked a question I literally answered in the post you quoted. You're asking more questions based on unrelated info, and your assertion that the OSS is just another VSS. Yes, technically it is, but they feed different systems, as I said, the OSS feeds the TCU, the VSS only feeds the cruise on RENIX, this is at least the third time I've said this, they have different names to differentiate between them.

The RENIX TCU knows what the trans output speed is because of the OSS. It doesn't care what the vehicle speed is, it doesn't need to know that to know when it's going to need to shift. It assumes it is in whatever gear it told the trans to be in.

Thank you, you finally answered my question. I just needed a larger set of teeth pullers, :laugh3:

Soooo, what prey tell is the REAL difference (other than possibly a simple linear X unit conversion factor) between the OSS speed and the VSS speed on a 2WD rig? I see non, if the tires are all on the ground, and the driveshaft is still connected.

And why wouldn't the OSS data to the TCU be considered confirmation as to what gear the AW4 is actually in?

What, never mind on that question, now I see, it just clicked, the engine speed (RPM) can change a bunch at say 35 mph, shifting from 2nd to third gear, while the vehicle speed stays the same. OK, Now I have connected the dots as to why the TCU does not know from just VSS or just OSS data what gear the transmission is actually in. Now I see that!!!! So my original question was not detailed enough to get at the answer I was looking for. I asked the wrong question......

Yes I get that they talk to different computers, but Detroit hates to pay for redundant expensive parts on vehicles, which is why I found it odd that they used so many of them.

But, if the TCU assumes it is in first gear as it instructed the AW4, and the TCU reads an OSS speed equal to say a Vehicle speed of 25 mph, the TCU would then use that data (feed back loop control) to tell the AW4 to shift to second gear right? I think that is what I was thinking, or trying to get at, when I asked the original question, I just screwed up the question and asked it backwards.

As the quote goes "Answer only important if ask right question", but it is not always easy to do that.

We need to keep that in mind when we try to answer questions here.

Now I am going to pick on you one more time. Are you sure about this statement you made?

"It (TCU) doesn't care what the vehicle speed is, it doesn't need to know that to know when it's going to need to shift."

I don't think that is right on a 2WD rig. If it is, explain it to me?

I see now that it can be the case on a 4WD with the variable of the transfer case you explained earlier in this thread....

But on a 2 WD rig, the VSS and OSS data are essentially the same data set (except for possibly a simple conversion constant multiplier).

 

[AJTorris]

Ok i had issues with my trans this weekend. ended up somehow loosing 3 bell housing bolts on the trail and the fourth was really loose. needless to say the trans shifted and broke an internal part, poured fluid out of the bellhousing (front seal destroyed) and also burnt up the trans fluid pretty good.

So i have been looking for a trans. I found a 99 Xj that was rolled for a decent price. (about the same im seeing around just for the trans). Now i know sensors are different and im sure the plugs are as well.

If i get the 99 could i swap all the sensors over to it and the tailhousing with the senor from my 93 along with the oblong part inside the tailhousing? Then that would keep my electrical harness and no issues with the plugs. Right?