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  #1  
Old April 12th, 2020, 13:34
da_jokker da_jokker is offline
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Angry 93 Cruise Control sporadic

About a month ago, my cruise control stopped working. I've been using it constantly since I've owned the XJ (about 2+ years) without issues.

It seems that the common cause is Vacuum.. so I did some checking and what-not and pretty much ruled that out. Primarily based on 3 things...

1) Everything else that uses Vacuum works fine (AC/Heater controls)

2) After leaving the XJ off for 30+ minutes, I can disconnect the vacuum line at the servo and hear the air sucking in.

3) Doing the Computer error check, it is reporting code 34 which maps back to some sort of Electrical Current issue.


With that in mind, and noticing that my Cruise Multi-function switch was really worn and the buttons seemed a bit "questionable"... I figured for $14, what the heck so I ordered one up and after about 15 minutes, had it installed.

Still, the cruise did not work. What I'm noticing is that when I first turn it on and attempt to use it, it will work 70-80% of the time. But after using it for a couple minutes, it just disengages and won't come back on. Next day (or sometimes even after coming back out of the store), it will work again 1 time only and for a very short distance.


Doing further research, I found a tech article that talked about how to test the Servo....

Using a Multi-meter, I tested the voltage at the servo... I would get 12v when the Cruise switch was on... 0v when it was off. In addition, the resistance for the ground was 0 ohms.

The article then suggested testing the server by applying 12v to a pin (#2 IIRC) and then ground the other 3 pins. Then, apply some vacuum to the Servo and the throttle cable should move... when I did this NOTHING. The Servo held the vacuum for as long as I wanted it to (using a hand pump). I could hear something inside it clicking when I applied the 12v... but nothing moved.

So figured that was my issue. $30 and 20 minutes later, I had a new servo in.. and obviously had that solved my issue, I wouldn't be writing this.

So here is what I think I know...

1) Cruise will come on briefly, sometimes. So it seems like that would rule out a blown fuse.

2) Brake light switch was replace 2 years ago (due to brake lights not working). They are currently working correctly (Pedal = On, No Pedal = Off). And I've held the pedal up with my foot while driving just to be sure and still no workie.

3) ECU reports a Code 34 which suggest it is electrical

4) Multi function switch and Servo have been replaced (Not factory, but both are NEW and not from a junk yard).

5) Vacuum seems to appear good with everything else working and lines maintaining vacuum long after the engine is shut off.

6) Being it is a 89-96 model, according to Haynes, my entire Cruise Control is ran by the Switch, Server, and ECU. I'm not supposed to have a Speed Sensor like the 84-88 models. (However there is something right near the throttle pedal hooked into what looks like the spedo cable... not sure what that is)



Not sure if I left anything out but I'm at a loss.
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  #2  
Old April 14th, 2020, 19:03
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tjmotter tjmotter is offline
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Re: 93 Cruise Control sporadic

A couple of things don't jive. My XJ is a '90 (which falls into the range your Haynes manual describes) and there are a couple of more parts involved:


1) there is a small vacuum activated switch above (IIRC) the brake light switch. It is not electric, it is vacuum and it is held in place by a round spring that is supposed to hold it into position. It has been known to slip out and every once in a while I have to reach up and push it back so that the actuator is in touch with the brake pedal


2) There is a small rectangular control module that is bolted to the lower dash plate. It is held in place with 2 screws and is responsible for managing the cruise control. It looks "kinda" like this: https://www.ebay.com/itm/1989-Jeep-W...x/123517894523. IIRC mine looks a little different but not by much. There isnt much in here but the contacts can corrode causing intermittent connections. The one in this picture looks like mine but the listing doesn't work: https://i.ebayimg.com/thumbs/images/...8Aq/s-l225.jpg


Your XJ is newer so it could be different but given how different mine is, I am not sure I would trust the Haynes Manual.



HTH
Todd

Last edited by tjmotter; April 14th, 2020 at 19:08.
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  #3  
Old April 15th, 2020, 13:04
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tjmotter tjmotter is offline
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Re: 93 Cruise Control sporadic

Note that Quadratec (usually has a good grip on the correct parts for XJ's), does list this speed sensor for a '93


https://www.quadratec.com/products/55200_0106.htm


Not sure if my '90 would be the same but there is a disconnect fitting in the area you describe that makes it a bit easier to install the speedo cable into the back of the dash. I don't think it has any wires coming out of it.
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  #4  
Old April 15th, 2020, 13:39
da_jokker da_jokker is offline
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Re: 93 Cruise Control sporadic

I'll have to go check under my dash and see what I can find..

According to Haynes...

84-88 do have what you described... A Cruise Control Module with a separate speed sensor, and a Servo that has a 6 wire plug.

On the 89-96, the ECU takes the place of the CC Module, and my servo only has 4 wires.


But I'll dig under the dash and see... FYI, a lot of my info came from

For Your Range...
https://jeep-manual.ru/index.php?page=78

For Mine...
https://jeep-manual.ru/index.php?page=300
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  #5  
Old April 15th, 2020, 13:45
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Saudade Saudade is offline
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Re: 93 Cruise Control sporadic

try these:

SERVO VACUUM
1) Remove cruise control cable from throttle body. Disconnect
cruise control servo 4-pin connector. Disconnect vacuum hose at cruise
control servo. Apply battery voltage to terminal No. 2 (Dark Blue/Red
wire) of servo connector. Using jumper wire, ground remaining 3
terminals of servo connector.

2) Connect hand held vacuum pump to servo vacuum nipple, and
apply 10-15 in. Hg of vacuum. Cruise control cable should retract and
maintain position as long as vacuum is applied. If servo does not test
as specified, replace servo.

VACUUM SUPPLY
1) Disconnect vacuum hose at cruise control servo. Install
vacuum gauge to disconnected vacuum hose. Start engine and observe
gauge. Vacuum reading should be a minimum of 10 in. Hg. Turn engine
off. Vacuum should continue to hold at a minimum of 10 in. Hg.

2) If vacuum is not as specified, check for kinked or leaking
vacuum lines, defective check valve, defective vacuum reservoir and/or
poor engine performance. If no problems are found, check cruise
control servo.
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  #6  
Old April 15th, 2020, 14:06
da_jokker da_jokker is offline
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Re: 93 Cruise Control sporadic

Quote:
Originally Posted by Saudade View Post
try these:

SERVO VACUUM
1) Remove cruise control cable from throttle body. Disconnect
cruise control servo 4-pin connector. Disconnect vacuum hose at cruise
control servo. Apply battery voltage to terminal No. 2 (Dark Blue/Red
wire) of servo connector. Using jumper wire, ground remaining 3
terminals of servo connector.

2) Connect hand held vacuum pump to servo vacuum nipple, and
apply 10-15 in. Hg of vacuum. Cruise control cable should retract and
maintain position as long as vacuum is applied. If servo does not test
as specified, replace servo.

VACUUM SUPPLY
1) Disconnect vacuum hose at cruise control servo. Install
vacuum gauge to disconnected vacuum hose. Start engine and observe
gauge. Vacuum reading should be a minimum of 10 in. Hg. Turn engine
off. Vacuum should continue to hold at a minimum of 10 in. Hg.

2) If vacuum is not as specified, check for kinked or leaking
vacuum lines, defective check valve, defective vacuum reservoir and/or
poor engine performance. If no problems are found, check cruise
control servo.

Thanks.. that is what I did and when the cable didn't pull, I replaced the Servo with a new one and still the same issue. I'm starting to wonder if my 93 (with only 55k miles on it) has somehow gotten the older version of Cruise Control in it. I'm going to look under the dash after work.
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  #7  
Old April 15th, 2020, 15:22
da_jokker da_jokker is offline
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Re: 93 Cruise Control sporadic

Ok.. took a look under my dash.. I think the extra things I am seeing have to do with my Anti-lock brakes.


I took some pics uploaded to my OneDrive:



So for example, in what I was thinking is my speedo cable (running along side the gas pedal)... there is the object in pic 20200415_145830.jpg

Then, looking up at the brake pedal, I see no vacuum lines.. just the brake switch I had to replace a couple years ago... pic 20200415_150034.jpg

Then there is this yellow fuse block.. (20200415_150216.jpg) not sure if that has some relay that is going bad for the Cruise Control..

and finally, a big Module, that looks to be for my Antilock brakes (20200415_150235.jpg)


Side note: that device in the cable has 2 wires.. one runs to an adapter connection in the fuse block by the kick panel, and the other wire runs up and into that Brake Light Switch (the red and white wire you see just above the switch)


So it would seem, other than that item in the speedo cable??? I don't seem to have the components for the older XJ.
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  #8  
Old April 16th, 2020, 10:42
da_jokker da_jokker is offline
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Re: 93 Cruise Control sporadic

I found out what the fuse block is... nothing about Cruise Control it looks like..

https://www.cherokeeforum.com/f2/hid...r-dash-169543/
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  #9  
Old April 16th, 2020, 13:24
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Saudade Saudade is offline
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Re: 93 Cruise Control sporadic

The first picture is your trans interlock. The cable runs to the shifter and prevents you from shifting out of park unless you depress the brake pedal.

Make sure your brake switch is adjusted properly as it will disengage the the cruise as well.
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  #10  
Old April 20th, 2020, 08:03
da_jokker da_jokker is offline
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Re: 93 Cruise Control sporadic

That is a very important tid-bit I did not know. I thought it was my speedo cable and that electrical component totally looked like the cruise control setup from an older XJ.

Watching a YouTube video (so you know it has to be correct, right? :P ) sounds like I can just unplug that thing to remove it from the equation.. just to see it if that is the issue. (Not safe I know, but just troubleshooting)

Seems like either the new servo is bad, or my issue might be the ECU
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  #11  
Old April 20th, 2020, 08:22
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Re: 93 Cruise Control sporadic

My '88 has the speed sensor in the speedo cable. It also has a separate CC module under the dash.
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  #12  
Old June 30th, 2020, 08:04
da_jokker da_jokker is offline
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Re: 93 Cruise Control sporadic

So it has been awhile and basically I just got tired of chasing my tail. This weekend I decided to at least attempt to once and for all at least narrow down the problem (or so I thought). Basically there are 4 wires going into the servo.. I figured I could rig something up to "monitor" those 4 wires and figure out what they were doing when (and if) it did work, and what they were doing when it did not.

So I used my Old Server to experiment on and was able to figure out the following:

Black Wire --> Ground
Blue/Red --> 12v whenever the Cruise was on (including Coast/Set/Resume)
Green/Red -->whenever grounded, it "held" the diaphragm in its current position
Tan/Red --> Whenever grounded, it "released" the diaphragm and allowed it to move

With this new found knowledge, I rigged up a wires that spliced into those 4 and were long enough to reach the cabin (just sticking out through the hood and into the passenger window (totally ghetto I know).

Long winded I know, but it was a frustrating head banger for sure...So anyway I go out on a test drive and was able to do some magic and get the cruise to work (at least temporary).. but here was the kicker... I could ground those two control wires and cruise would work for a second.. then when I tried to ground them again.... nothing. So I go back to the house and while in the garage, all of a sudden they start to work again... I was like WTF.

So I went out again, but this time instead of using a test light to ground wires (the light not only prevented me from shorting something, but I could visually see it working) I used a Voltmeter... and BINGO!

When my cruise control was working, I was getting 10-12 volts on those "Control Wires". When it didn't work I was only getting 3-4 volts on those same wires. So then my own light bulb when off and I switch my voltmeter to monitor just the Blue/Red wire and saw the exact same thing... All my troubleshooting before showed this was getting 12v. But after a few seconds of working, my Cruise would stop. And now I knew why...

So looking at the wire diagrams, the Blue-Red wire actually goes to the Brake Light switch (which I had to replace 2 years ago because my brake lights stopped working) From there the Blue-Red turns into Yellow-red and goes to Pin 49 on the PCM.

So now I had a heart attack.. thinking that my PCM was bad and was not sending the full 12V down to the servo. So my next step was to monitor the voltage going INTO the PCM. So I pulled out my Brake light switch, tapped into the Yellow/Red wire, and then put everything back together.

This is were it gets strange... So then I hope in the jeep and go for a test drive, and I drive and drive.. works every time. Drove it the next day.. works. What used to fail guaranteed in just a couple of minutes, I could not get to act up.

Hopefully I didn't just curse it, but my working theory now is that inside the Brake Switch there is an independent circuit that does the opposite for the brake lights. In other words, when you press the brake pedal, it cuts power to the Blue\Red wire. When you release the brake, it provides 12V.

So I'm thinking that my Brake switch had moved just a bit (since it really is not bolted in) to so that when I released my brake pedal, the pin we far enough in to turn off the brake lights, but now quite enough in to provide the full 12v to the Cruise. Heck, maybe it wasn't providing any voltage and the 3-4v I measured was backfeed.

Regardless, when I put everything back together under my dash, I used a Zip tie to help support the Brake light switch so that it would hopefully not back out anymore.

So far so good....

Would this be a good time to mention that I'm seriously considering that new Bronco
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  #13  
Old July 3rd, 2020, 03:52
alexbrown64 alexbrown64 is offline
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Re: 93 Cruise Control sporadic

Good feedback. Yep, the cruise is deactivated by the brake switch, so makes sense now that the misadjusted switch was the cause. Well done. I will put that one in my memory for the future as I use my cruise all day everyday too.
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