Cruise control doesn't work on 1998 TJ

D

Dean2

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Nov 13, 2019
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7
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Peoria AZ
Reviewed many threads with no joy. Dash diagnostic shows cruise light but it doesn’t show when initially starting the engine (like airbag and engine check). Pushing steering wheel ON does nothing - no light flicker. Just replaced clockspring which got the horn and airbag working (I did get the airbag clockspring as it has the third connector). Physically have all the parts and hoses. Engine runs well so don’t think I have a vacuum issue (plus the vents work correctly for heat and A/C.

1998 TJ 5 speed manual 4.0L

Very open to next step suggestions
 
Dean2 said:
Reviewed many threads with no joy. Dash diagnostic shows cruise light but it doesn’t show when initially starting the engine (like airbag and engine check). Pushing steering wheel ON does nothing - no light flicker. Just replaced clockspring which got the horn and airbag working (I did get the airbag clockspring as it has the third connector). Physically have all the parts and hoses. Engine runs well so don’t think I have a vacuum issue (plus the vents work correctly for heat and A/C.

1998 TJ 5 speed manual 4.0L

Very open to next step suggestions
Click to expand...
Also did a PCM reset (30 secs pos batt cable connected to meg, then engine asst to ON, headlights turned on/off the ignition back to off
 
I recently did this on my '98, so I'll try to help. Walk us through what you've done so far - did you install all the new cruise components, or were some of them on the Jeep already?
  • Clockspring (you just put a new one on - did the old one have the green plug?)
  • Steering Wheel Switches
  • Servo
  • Wiring Harness
 
Thanks - more context. Jeep is new to me so don’t know if CC worked or not. Factory install, switches on sides of steering wheel bottom. They appear fine. Clock spring (old and new) had green wire connected to switch harness. Jeep is in great condition and all the parts look fine. Vacuum hose out reservoir looks/feels fine. Followed all the thin vacuum hoses and nothin readily apparent. Solinoid/actuator looks fine and is connected to throttle. Went thru all the fuses (engine compartment and behind glove box) and added some to the Assy slots that were previously empty (just in case). Reset PCM per correct process and now running like crap as it relearns so pretty sure I did it right. Brake lights are not on all the time so think switch is OK. All lights are LED but have appropriate relay to stop the fast flash it originally had. When I do the dash diagnostic (turn assy on, press odometer and hold, and then turn ignition switch between off and on 4? Times) the “cruise” light does come on so I know it is good. However, at no other time do I see the cruise light - not when I first start the Jeep (am I supposed to?) nor even a short flash when trying to turn cc on

AC and heat work fine through all three paths - defrost, central and floor

Engine is not rough and idle is consistent but if open to suggestions even if it’s to start replacing line or a ‘check valve “
 
Dean2 said:
Thanks - more context. Jeep is new to me so don’t know if CC worked or not. Factory install, switches on sides of steering wheel bottom. They appear fine. Clock spring (old and new) had green wire connected to switch harness. Jeep is in great condition and all the parts look fine. Vacuum hose out reservoir looks/feels fine. Followed all the thin vacuum hoses and nothin readily apparent. Solinoid/actuator looks fine and is connected to throttle. Went thru all the fuses (engine compartment and behind glove box) and added some to the Assy slots that were previously empty (just in case). Reset PCM per correct process and now running like crap as it relearns so pretty sure I did it right. Brake lights are not on all the time so think switch is OK. All lights are LED but have appropriate relay to stop the fast flash it originally had. When I do the dash diagnostic (turn assy on, press odometer and hold, and then turn ignition switch between off and on 4? Times) the “cruise” light does come on so I know it is good. However, at no other time do I see the cruise light - not when I first start the Jeep (am I supposed to?) nor even a short flash when trying to turn cc on

AC and heat work fine through all three paths - defrost, central and floor

Engine is not rough and idle is consistent but if open to suggestions even if it’s to start replacing line or a ‘check valve “
Click to expand...
check for vacuum leaks it might be not too bad but just bad enough to cause your cruise to not work
 
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Dean2 said:
How do I systematically check the vacuum system?
Click to expand...
Start with a visual inspection i believe the most common spots are near the 2 and 8 check for cracks in the lines as they are plastic and dont really age well if you dont find anything with a visual inspection id move onto a fogger tomcheck for vacuum leaks id refer to chris with questions about how to do that

1BB66402-B2D8-4E8E-9992-9E6A6BC5A11B.jpeg
 
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Vacuum testers are cheap and would make checking things easier for you. When i did the cruise on my 98 one of the issues I ran into was the used vacuum module I bought from a wrecking yard was no good. It had the same symptoms as you described. Turns out the diaphram had cracked. In addition if the cruise is a addon that a po was putting in and gave up on, the wrong year switches will cause the same issue. They look the same but you do need the correct year.
 
A smoke test is a great way to check for vacuum leaks you would otherwise not be able to find, as many are invisible to the naked eye.
 
Got a vacuum gage and found many leaks so replaced all hoses and valves. cruise control servo also had a vacuum leak so was replaced - end result is solid vacuum system.

also replaced the CC switches but still no light on dash or setting of speed.

what is next? Looked at all fuses although I don’t know which specific one may be involved.
Dean
 
What part number are the switches you used? If they are the correct year the next step will be to test the wires from the switches and the vacuum module to the computer. Start will the continuity through the clock spring.
 
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Pn 39754D was the original switch. The dash light never comes on normally but it does during the cluster diagnostic.
How do I trace the wires from the clockspring? Remove the connector off the servo and look for continuity?
 
If you pull the clock spring you can use a ohm meter to check each of the wires through the switch for proper continuity. They are fairly delicate so center your steering wheel just before you pull it and use some masking tape to keep the inner and outer rings of the switch in place while testing and until your ready to reinstall. If your really carefully you can always turn it one way until you get light resistance then count the turns the other way until you get the same light resistance and split the difference to find center but it is easy to over do it and range the clock spring if you don't go easy.
 
Almost gave up but gave it a go again today. Key interesting finding is that the green wire from the clock spring is only giving out 5v. Don’t know if normal but seems strange.

ReplaceD all vacuum lines and servo unit - no vacuum leaks per gauge. All fuses check and pulled/reseated. Removed and cleaned engine and firewall ground points.

Still no cruise light during startup check. Idea’s before I mess with the
PCM?
 
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It's a can bus system so 5volts would be correct if the there is continuity thought the clock spring for all the wires, I would check each wire from the PCM to the clock spring and the vacuum module before assuming there is a issue with the PCM. The downloadable manual will show you what pins are the ones for the cruise system. If I was at home I could tell you in fairly short order but I'm away for Christmas and do not have the print out I worked off with me to do the cruise in my 98.
 
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