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1998 Jeep TJ Wrangler Airbag Light On and Cruise Control Not Working

Jeep Wrangler Jeep TJ Jeep how-to

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#1 jj_jeep

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Posted 26 August 2013 - 08:00 PM

My TJ airbag light has been on for some time and the cruise control no longer works.  I assume they're related, but I'm not sure.  Some corners of the internet say the clock spring needs to be replaced. 

 

I know CC works with manifold vacuum.  I tried to trace the vacuum lines to look for abraded hoses or leak points and found none, but there are a lot of lines running a lot of directions - is there a common place they leak? 

 

Can this be diagnosed at home?  Or is it best to have the dealer plug in their diagnostic computer? 

 

Is the airbag REALLY safe after the battery is disconnected for a few minutes?  Or is it best to let the pros handle this one of it is the clock spring? 



#2 Moses Ludel

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Posted 27 August 2013 - 12:48 PM

The airbag system is a safety issue.  The consequences of a malfunctioning bag or the unexpected deployment of a bag is a serious matter, and the mere thought makes us nervous.  Since the Air Bag system can be scanned, that would be a consideration.  There are other possibilities, but a specific air bag light signal is a concern.

 

I recently did two repairs on the '99 XJ Cherokee, one related to instrumentation/gauges, the other related to the heater and A/C vent controls.  The instrumentation issue was wiring behind the panel and plug connections.  For both of these malfunctions, there were factory TSBs from Chrysler, and the instrument panel issue was common to the 1998/99 era XJ Cherokee and the TJ Wrangler. 

 

I mention this because on my XJ, the Air Bag light was part of that malfunction.  See the how-to repair at the magazine: http://www.4wdmechanix.com/How-to-XJ-Cherokee-Erratic-Gauges-Fix.html.  I bring this up because your Air Bag issue could be a plug connection issue at the panel.  The simplest fix I found online is to unplug and plug the panel at its connectors.  When this does not suffice, the repair in the article was my solution.  Check this out, JJ, it's certainly a possibility.  I'd try the unplug/plug approach first, changing out of the plug gets involved.  Always disconnect the battery negative cable with this kind of work.

 

The other TSB was about actuator motors for the heater and A/C vents.  I covered this quite thoroughly in another article:  http://www.4wdmechanix.com/How-to-Jeep-XJ-Cherokee-Air-Conditioning-Fix.html.  This one got interesting.  As it turned out, the actuators were just fine (bought a vacuum motor beforehand, now have a spare), but the vacuum circuits were not.  See this article, as your TJ has a similar system, and my quick troubleshooting technique for a full circuit vacuum check works well.  The A/C vents, cruise control and other circuits all depend upon the vacuum reservoir behind the front bumper.  You'll see the relationship at the article.  As a point of interest, the vacuum leak was in damaged tubing not far from the battery box.

 

The vacuum circuit leak test will require a hand vacuum pump, which is a valuable diagnostic/troubleshooting asset.  Follow my guideline, you have a similar system and access to the vacuum tube that attaches at the intake manifold.  The cruise control apply vacuum can also be tested with your vacuum gauge, using the running engine as a vacuum source.

 

So, the Air Bag light could be just that:  A wacky Air Bag light from poor instrument panel connections.  Or, you could have more going on...We're back to the need for a diagnostic scan tool that covers powertrain, ABS and, yes, Air Bags!

 

Moses



#3 biggman100

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Posted 28 August 2013 - 02:27 AM

JJ, i would like to add to this if i may. I doubt the air bag and CC are related. I just finished some major work in the spring on a 99 cherokee that a guy bought basically sight unseen. After replacing the engine, fixing a shift solenoid in the transmission, and replacing almost everything in the rear brakes, the ABS light, and airbag light were both on. The airbag light was traced by the dealer to a faulty sensor in the front. The ABS was a bad wheel bearing and sensor. Anyway, after all that was fixed, the CC worked for 2 days, and then just quit one day. After checking fuses, wiring, and a bunch of other stuff, i sent it to the dealer, who traced it to a bad brake light switch. I'm not saying that is the issue with yours, but the dealer i took it to said that is common on a lot of the 1997 to 2002 Jeeps, so it is worth looking into.

 

Now as for the air bag light, that is on a different circuit entirely than the CC circuit. i wouldn't suspect the clock spring, unless you know for sure that someone has had the steering wheel off, and did it improperly. The best bet would be to find a scan tool that will test the air bag system, or have it checked by a dealer. In the case of the 99 i did, i had the dealer scan it, and give me a diagnosis, and then i did the repair myself, which is what i usually do on systems my scanners wont read. The issue i have found with a lot of the pre 2001 vehicles is that most scanners are spotty on ABS and air bag tests, even the scanners i have, so i have found it is just less of a headache to have it checked by a dealer. My Snap On MT2500 could probably be updated to do those vehicles, but this is the first Jeep i have worked on in years, so i cant see spending the money for that upgrade.



#4 jj_jeep

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Posted 01 September 2013 - 08:06 PM

I've had the "dead gauges" many times over the years and I knew it was a flakey connector.  I didn't know it could relate to my airbag light, so I called the dealer to see if they had the connector.  Otherwise, I was just going to try the unplug and clean up approach.  The connector is only $10 and I'm okay with soldering, so I picked up a connector and replaced it this weekend.  The results are a mixed bag, I should never have the instrument cluster conk out on me again, but the pesky airbag light is still on.  The airbag fuses in the glove box were good. So Biggman it looks like I'm in the same boat you were.  Not sure where the brake light switch is located.  Might have to give in to the dealer on this one.   

 

Regarding the cruise control.  Moses, since I had the vacuum gauge already, I tried your suggestion of checking the vacuum at the cruise control vacuum motor gadget on the drivers side of the TJ.  The vacuum measured the same as a direct connection to the manifold, so the good news is the vacuum is ship shape.  Had I thought of it, I would have checked the cruise control light on the instrument cluster when I had the cluster out because that light has worked intermittently for years even when the cruise worked fine.  So I don't really know - it could be the cruise switch in the steering wheel, or something else.  I could not find a fuse labeled cruise control to check.  I really miss cruise, so I might have to have the dealer check this one too. 



#5 Moses Ludel

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Posted 02 September 2013 - 08:20 AM

Well, the dash connector was an issue, so replacing it was worthwhile, great that you solder, JJ_Jeep, these are resourceful skills that pay off!  Sounds like a diagnostic check of the Air Bag system would be wise, for sure.

 

On the cruise control issue, you were at the "T" for the cruise unit.  Check the reservoir vacuum seal from that same "T" to the bulb/reservoir at the front of the Jeep.  A quick check for the entire system can be performed from the engine vacuum line that attaches at the intake manifold.  Trace from the cruise to that elbow with the vacuum tube. 

 

Hook up your vacuum gauge/pump there, and pump down vacuum.  The entire system should hold vacuum.  If not, the leak is somewhere between the intake manifold and the reservoir.  Possible bleed-offs or leaks from that circuit would be the heater and A/C vent controls, the cruise vacuum circuit, the one-way check valve for this vacuum circuit and the reservoir bulb itself.

 

If you're curious about the trouble areas for the cruise control, this is the "factory" approach to a defective speed control system:

 

If a road test verifies a system problem and the speedometer operates properly, check for:

  • A Diagnostic Trouble Code (DTC) If a DTC exists, conduct tests per the Powertrain Diagnostic Procedures MDS2.
  • A misadjusted brake (stop) lamp switch. This could also cause an intermittent problem.
  • Loose, damaged or corroded electrical connections at the servo. Corrosion should be removed from electrical terminals and a light coating of Mopar MultiPurpose Grease, or equivalent, applied.
  • Leaking vacuum reservoir.
  • Loose or leaking vacuum hoses or connections.
  • Defective one-way vacuum check valve.
  • Secure attachment of both ends of the speed control servo cable.
  • Smooth operation of throttle linkage and throttle body air valve.
  • Failed speed control servo. Do the servo vacuum test.

As you know, I like to start with the easiest prospects first before parts replacing!  Check for a vacuum leak, either tubing or the reservoir bulb itself, each can be confirmed with your nifty new vacuum pump tester.  Check out the brake light switch function and the switch point for the brake lamp switch.  Make sure you do have electrical current, try to find that fuse circuit, and if you can't find it readily, let me know, I'll provide information.

 

I can also provide more information on each of the systems mentioned.  A vacuum check at the cruise servo can confirm the "one-way check valve" function as well as the speed control servo condition.  Check vacuum at the "T" near the cruise servo in all three directions:

 

1) Cruise servo (only) direction as you did.

2) Check the combined servo and check valve*, using the "T" end facing the reservoir.

3) Check the "T" end to the reservoir to isolate and test the reservoir tube and reservoir bulb only.

4) If the reservoir feed line leaks down, isolate the reservoir itself and vacuum test it.

 

*The check valve is an inexpensive item.  This trouble spot traps the manifold-to-reservoir air in the system and prevents vacuum fluctuation.  It is a simple one-way valve located between the manifold and the first junction of the cruise and heater-A/C vacuum circuit.  The check valve helps stabilize vacuum, otherwise manifold vacuum fluctuates widely.  Visualize the vacuum "trapped" between the reservoir and check valve, with the recharge of vacuum coming from the manifold source.

 

Let's look for a simple fix before parts replacing, JJ.  From my article, you can see how a split in the vacuum tube from the reservoir to the cruise "T" was enough to keep the XJ Cherokee's cruise and vents from working when the engine was under throttle.  A defective check valve would have a similar effect.

 

Moses



#6 jj_jeep

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Posted 05 September 2013 - 06:37 PM

The "stop lamp switch" looked pretty easy to check out.  I had a few minutes tonight, so I pulled it out of the Jeep and pinned it with my multimeter in continuity check mode.  The pair nearest the plunger (and brake pedal) was normally open.  The other two pair were normally closed.  They switched when I depressed the plunger. 

 

I assumed the pair running the stop lamp circuit was normally open (closed when the pedal and plunger were depressed) and the pair for the cruise would be the same way.  I'm not sure what the normally closed pair would be.  But the fact that all three pair "switched" when I pressed the plunger led me to believe the stop lamp switch was functioning correctly.  Any reason to believe otherwise? 

 

Related to the vacuum...  I haven't had a chance to check anything else, but would it be a good sign that the check valve was working if I heard a lot of air rushing in when I pulled the vac hose connector off the cruise control module?  I was thinking that was a good indicator that the system was holding vacuum. 



#7 Moses Ludel

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Posted 05 September 2013 - 08:15 PM

Sounds like the pedal switch is okay.  The adjustment of the pedal and switch position determines when the switch opens and closes.  Presume you checked this, JJ.  It's easy to do by simply watching the brake (tail) lamps apply as the pedal depresses.  The pedal often sags with age, sometimes causing the switch to stay open, when that occurs, the brake lights would be on.  Check this if necessary.

 

As for the one-way vacuum check valve, when you disconnected the vacuum hose at the cruise control end, you should hear or feel suction from the intake manifold.  This was correct...However, it only tested the "open" direction of the vacuum check valve.

 

The check valve must also hold that vacuum in the circuit when manifold vacuum drops.  A quick way to test this with the engine running would be with your vacuum gauge attached at that same point as before.  With the engine idling, you will get that 18-21 in/hg vacuum you're used to seeing. 

 

Make sure the vacuum gauge seals properly, then shut off the engine.  While vacuum at the manifold will drop to zero, vacuum in the circuit between the cruise servo and the one-way check valve should remain steady—to whatever vacuum setting the one-way check valve normally holds. 

 

Let us know what your check valve holds.  It must be high enough to provide adequate vacuum for the cruise and the heater-A/C vent controls.  Test vacuum to the reservoir with the hand pump attached to the intake manifold tubing elbow—as I described earlier.

 

We'll go from there...

 

Moses



#8 jj_jeep

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Posted 08 September 2013 - 07:04 PM

I had a little more time to tinker this weekend.  I pulled the hose off the cruise control servo and plugged in my vacuum gauge.  I verified the I got about 18 in Hg at idle.  Then I shut off the engine, as you suggested, Moses, and it held the 18 in Hg.  My gauge didn't come with a hand vacuum pump, but it did come with a "T" fitting.  Is there a way to check the reservoir by "T-ing" into the vac line but using manifold vacuum as the vacuum source instead of a hand pump? 

 

I did try my HVAC controls just as an additional check that I could do today and they worked, although it was a little slow to go from one of the settings to another (I think it was full defrost to panel).  And all settings had a little bit of ventilation coming through the floor vent. 

 

Lastly, all fuses in the central fuse box by the battery.  These are not labeled in the box cover, so I don't know if one of them is for the cruise or not.  The fuses in the glove box are all good.  Is it possible there's an inline fuse for the cruise somewhere? 

 

I feel pretty good about the stop lamp switch unless the timing is really subtle.  That is to say, I press the brakes and the brake lights come on.  I release the brakes, and the brake lights turn off. 



#9 Moses Ludel

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Posted 08 September 2013 - 08:47 PM

JJ_Jeep, your idea of a "T" is excellent.  Place the gauge anywhere between the reservoir and the check valve.  Use engine vacuum as your source instead of a hand vacuum pump.  When you shut off the engine, vacuum should hold for quite a while from the reservoir to the check valve!

 

Note: Think of a vacuum circuit like a wiring circuit:  continuity is continuity, and if there are no "opens" (i.e., leaks in the case of vacuum), the system is sealing.

 

As for the cruise control, below is the factory wiring schematic for your '98 TJ Wrangler cruise control circuit.  See if this answers any questions.  If not, let me know what you need, I'll dig deeper.

 

Attached File  TJ Cruise Control Wiring.gif   21.46KB   1 downloads

Wiring schematic for cruise control circuit on 1998 Jeep TJ Wrangler, click on image to open up. (Courtesy Jeep/Chrysler)

 

Moses



#10 ttippetts

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Posted 15 January 2014 - 09:51 AM

I don't know if you ever found any resolve to your problem, but I did once have the exact same problem as you except that my horn did not function either.  It was the clockspring.  At the time (~2 years ago) the clockspring was on national back order.  I bought a used one online and installed it myself and all works great.


Tracy (ttippetts)


#11 Moses Ludel

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Posted 15 January 2014 - 02:31 PM

TTippetts, welcome to the forums!  Thanks for outlining this clock spring solution.  The clock spring has turned up for a variety of issues, and these comments are very helpful.  Looking forward to your participation...

 

Moses



#12 jj_jeep

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Posted 16 January 2014 - 08:08 PM

Thanks ttippets. My airbag light is still on. I've wondered about the clockspring because my cruise doesn't work and then the airbag light is on. I was trying to figure out how to pin down if it was the clock spring. I wonder if I damaged the clock spring a while back when I replaced the steering gear. I thought I was careful, but maybe it's touchy? I like your suggestion of buying one online and replacing myself. You have to get a steering wheel puller, right?

#13 Moses Ludel

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Posted 17 January 2014 - 09:57 AM

Hi, JJ_Jeep, and Happy New Year! 

 

I'll defer to TTippetts on your clock spring questions...If you need safe practices for removing the steering wheel, let me know.  Beware of the airbag issues, we'll stick to the factory procedure here...Let's make sure you don't get knocked silly by a deployed air bag!

 

Moses



#14 ttippetts

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Posted 30 January 2014 - 02:56 PM

Yes you need a puller, you can use a harmonic balancer puller.  Be sure to disconnect negative battery terminal.  There is a youtube video of one being done on a Cherokee, but they are the same.  Oh, make sure to get one (clock spring) for a cruise control equipped model as they are different.

http://www.youtube.c...h?v=VxYHC6oX6eQ


Tracy (ttippetts)




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