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Cruise Control not working


Tim Reatta
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Working through the repair list on my 1989 Reatta. The cruise control stopped working after the car was brought out of hibernation. The cruise light does go on. I researched on the forum (thank you Ronnie and many others) and ran the owner codes and then the GM tech codes. I could find no errors. There was a historical C553, not sure what that is for, but it was marked historical. 

 

I pulled the servo out tonight and ran the ohm tests shown on the forum and checked the vacuum. It passed with flying colors. The bellows sucked in readily. I put my Mityvac on the small hose coming off the servo and that side held 10+. Same for the large hose. I checked the vacuum tank independently and it held. 

 

Not sure where to go from here. Any help or suggestions would be greatly appreciated. 

 

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This the information  have been looking for . I have been trying to figure out why my cruise will not work.

Mine seems to work until the engine warms up, but it could be until I use the brakes the first time.

I do have LEDs in my third light.

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On 4/5/2020 at 12:21 PM, SpecialEducation said:

Check yer 3rd brake light bulbs. If resistance on that circuit is not in the proper range, cruise won’t engage. LEDs are a no-no here, unless you add a parallel resistor to drop the resistance. 

It will be interesting to see if the 3rd brake light bulbs are the cause of the cruise control not working.  When I look at the wiring diagram I can't see any relation of the 3rd brake light bulbs to the cruise control but I'm not saying the bulbs aren't causing the cruise not to work.  If someone finds out the bulbs are the problem please let us know.

Edited by Ronnie (see edit history)
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I have not traced the Reatta wiring specifically, but typical GM cruise control monitors the circuit from the brake switch end. There was a TSB for the early ‘90s wagons because bad contacts (high resistance) at the hatch would cause cruise to randomly drop. The fix was to put a resistor in the circuit, parallel to ground ahead of the bulbs; 390 ohms, I think. This dropped the resistance of the circuit within acceptable range whether the HMSL was connected or not.   

 

Edited by SpecialEducation (see edit history)
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I have reinstalled the vacuum servo, cleaned the terminals (used electrical conduit cleaner and mild abrasive) and the fuse was fine. The cruise control still does not work. I did not check the third brake light as it has not been changed to an LED. Was this a mistake? When I got the car the brake lights did not work and I did replace the brake light switch which fixed that problem. Not sure if I need to check anything else in that area or where to go next. The cruise light is on. I suppose there could be a problem with the switch on stalk. Perhaps some type of electrical check at the servo cables?? Also, I did notice an electrical female plug with a green cover near the vacuum tank. It is not plugged into anything and I could not find a "home" for it. Any guidance would be appreciated. 

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1 hour ago, Tim Reatta said:

Not sure if I need to check anything else in that area or where to go next. The cruise light is on. I suppose there could be a problem with the switch on stalk.

 

I can lead you through the process of troubleshooting the stalk if you decide you want to do that.  It can be done through the Reatta's onboard diagnostic system. Are you familiar with using the diagnostic system?  If not, go to ROJ and look over the Diagnostics Booklet. It's your best friend when troubleshooting your Reatta.

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2 minutes ago, DS_Porter 89 Burgandy said:

When I bought my '89 it only had 24K miles on it. Very nice except the cruise control did not work. The brake pedal has a vacuum switch which releases the vacuum and causes the cruise to quickly drop out when the brake is applied. Check that. Hardest part is getting your eyes and hands on it

What did you do to fix it. Replace the vacuum switch?

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I am having the same trouble with my cruise control, only mine works the first time you turn it on.

Then it seems like when it warms up a little it just drops out. I have checked the system and replaced most all of the parts with no luck.

I do have LEDs and regular bulbs in the third brake lights and in the tail lights.

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Hi Ronnie:

I did go to your site and got the data to check the servo. The electrical readings were perfect. Also, when I applied vacuum, the bellows responded very well. Also, I looked at the 1989 diagnostics. I ran the owner and then the GM tech. No codes came up except for a historical one. If you or anyone has some other tests for me to run, that would be great. I tried it again to today and no luck. I was over 35 mph and nothing changed on the CRT. Being a beginner, I was thinking perhaps electricity is not getting to the servo connections? Just not sure what the next test should be. Thanks to all.

 

Regards:

 

Tim

 

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43 minutes ago, Tim Reatta said:

I ran the owner and then the GM tech.

 

I'm not sure what you mean. Are you using the onboard diagnostic system built into the CRT? Here is how to access it. If the GM tech is a scanner I recommend using the onboard diagnostics instead. It will give you BCM codes that are related to the cruise control as well as allowing you to do a lot more than any OBD1 scanner I have seen. Use the link above and write down any codes the diagnostics display and post them here. After that I will lead you step by step through the process of checking the cruise control problem.

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This is the first steps I would take in troubleshooting the cruise control to see if it is functioning electrically as it should.  Begin by turning the key to the run position and press the cruise button on the headlight switch to activate the cruise control. Make sure the light on the button is glowing. The following assumes it is.

 

  1. Enter Onboard Diagnostics and allow it to go through the cycle of displaying codes.
    (Write down any codes and post them here if you haven't already done so.)
     
  2. When the CRT asks ECM? press NO.   When it asks BCM? press YES.
     
  3. When it asks BCM Data? press NO.  When it asks BCM Input? press YES.
     
  4. On the BCM Input screen start pressing the YES button to scroll through the BCM inputs until you come to C/C Brake - BI71.  It should read HI.   Press the brake pedal and it should go LO while the pedal is pressed.
     
  5. Press YES again to view C/C ON-OFF - BI75.   It should read HI when the cruise is on, (the headlight switch cruise button is illuminated), and LO when you turn the cruise off.
     
  6. Press YES again to view  C/C SET/CO - BI76.   It should read LO.  Press the button on the end of the stalk and it should go HI.
     
  7. Press YES again to view C/C RES/AC - BI77.   It should read LO. Press the resume button on the front of the stalk and it should go HI.

 

Do all the inputs react as described above?

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Ronnie:

 

Thank you. I am working on a house project currently, but I will try the steps listed and report back to the forum tonight or tomorrow morning. When I said "GM tech" diagnostics I meant the directions from your web site about using the climate control section to enter the diagnostics for GM mechanics. 

 

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Well the house project took longer than expected but I ran the Reatta through the tests tonight.

 

Codes: History B 671 and History C 553

The first is a Servo Position Sensor Circuit Problem (Cruise) I did remove the cruise control servo to run the electrical tests and the vacuum tests. I think I reinstalled it correctly. Fairly simple install.

The second is CRTC Memory Reset Indicator

 

Step 4: C/C Brake - BI71. reads LO not HI. Then when brake pedal is pressed it does not change, it stays on LO.

 

Step 5: C/C ON-OFF BI75 it does read HI. And then goes to LO when cruise switch is turned off.

 

Step 6: C/C SET/CO BI76 it does read LO. Pressing the end of stalk button and it stays on LO, does not go to HI as it should

 

Step 7: C/C RES/AC BI77 it does read LO. When the resume button is pressed it stays on LO, does not go to HI as it should.

 

So, I will have to admit I do not know what all of this indicates, but perhaps at least there is a problem with the stalk controls??

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2 hours ago, Tim Reatta said:

Codes: History B 671 and History C 553

The first is a Servo Position Sensor Circuit Problem (Cruise) I did remove the cruise control servo to run the electrical tests and the vacuum tests. I think I reinstalled it correctly. Fairly simple install.

The second is CRTC Memory Reset Indicator

The code B671 may go away when you correct the problem in Step 4 below. Don't worry about the code 553 in history.

 

Step 4: C/C Brake - BI71. reads LO not HI. Then when brake pedal is pressed it does not change, it stays on LO.

I'm thinking this is probably the reason your cruise control isn't working. The BCM thinks you have your foot on the brake. You might have other problems too but this must be corrected before you go any further. Either you have a bad switch, a switch that is out of adjustment or the wrong switch. It could be the wiring but not likely. 

 

EDIT: This isn't the same set of contacts that turns the brake lights on. I haven't looked under the dash of my car to check but I think it may be a separate switch from the brake light switch.

 

Step 5: C/C ON-OFF BI75 it does read HI. And then goes to LO when cruise switch is turned off.

This is normal operation.

 

Step 6: C/C SET/CO BI76 it does read LO. Pressing the end of stalk button and it stays on LO, does not go to HI as it should.

This is normal if the brake switch isn't working properly. My car does the same thing if I hold my foot on the brake pedal.  I think this input will start going HI as it should after you correct the problem with the brake switch.

 

Step 7: C/C RES/AC BI77 it does read LO. When the resume button is pressed it stays on LO, does not go to HI as it should.

Same answer as #6 above.

 

So, I will have to admit I do not know what all of this indicates, but perhaps at least there is a problem with the stalk controls??

I think the stalk is probably OK. Run tests 6 and 7 again after you get the brake switch problem corrected and I think it will test correctly. Power goes through the brake switch before it goes to the stalk.

 

Edited by Ronnie (see edit history)
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Problem solved! Thank you Ronnie and all of the other contributors to my dilemma.

 

Last night I built a fire ( a bit cold in Ohio) and sat down with Ronnie's test sequence and the two factory manuals. I was able to find the testing sequence (manual 2) and wiring diagrams. I then matched up Ronnie's steps to the correct section in the manual. The manual will give suggested paths to follow to correct the incorrect reading. The BI71 test mentioned a step (check to see if the brake light switch is correctly adjusted). Well, I put the brake light switch in a few years ago when I bought the car (brake lights were not working on the drive home). So, with it being about 3 years old, I thought the odds of it being defective were not good, but possible. Also, they had other tests with a fuse link that I considered. I figured somewhere in the 1600+ pages of manuals they tell you how to adjust the brake light switch, but I thought first I will just go out to the garage and look at it and try to reason things out.

 

The switch had a tube like end with ridges in it (plastic). This inserts into a thin circular stamping that holds it in place. The only way to adjust the switch would be to push it further in the stamping or pull it further out. So, I took the switch out of the stamping and got a lightweight clamp to place on the switch to hold the button all of the way in. This would duplicate the normal position of the switch before you press the brake pedal. I then ran the test and no problems. When the clamp was released, replicating pressing the pedal I got the correct response. 

 

So I reinstalled the switch and pressed it in a few more "clicks" so the button would be fully pushed in. A quick test drive indicated the cruise was like new again with correct responses and dash lights responding for each cruise state. As a side note, all of this work is done up under the dash, not a very comfortable area to be working in. I found one of those small mirrors on a telescoping stick in my tool box. That and a good LED light made seeing, adjusting, etc. much easier. I had another learning experience in this process. When testing the vacuum on the vacuum tank you have to pump the Mytyvac many times. The other lines only one or two pumps bring it up past 10 to see if it will hold vacuum. I thought that was my problem so I now own a second vacuum tank that is not needed. Anyone needing a good used tank I have one. 

 

Thanks Ronnie, I am not so intimidated by the manual. I think I could be dangerous at further diagnostics. I saw a BCM input for the wind shield washer. Currently, my CRT keeps telling me the washer fluid needs to be filled when it is to the brim. I have checked and the float is moving up and down. All of the washer functions just fine. So, I will be spending another night reading the manual to see what test I might run to determine why I am getting this error.  

 

 

 

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Jim:

I watch several forums as a caraholic, and the men and women of this forum are great. My Reatta sat in the back of the British Car Museum for several years due to a garage construction project that went awry at my new to me house. I am now just beginning to spend some quality time with the car. I really enjoy driving the Reatta but this forum adds to the experience and makes ownership of an older vehicle much easier. I hope this thread helps others down the road as it specifically solved my problem. There are many good ideas to check in it besides my eventual outcome. 

 

Regards:

 

Tim

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On 4/16/2020 at 6:49 PM, Tim Reatta said:

... I figured somewhere in the 1600+ pages of manuals they tell you how to adjust the brake light switch, but I thought first I will just go out to the garage and look at it and try to reason things out.

 

The switch had a tube like end with ridges in it (plastic). This inserts into a thin circular stamping that holds it in place. The only way to adjust the switch would be to push it further in the stamping or pull it further out. So, I took the switch out of the stamping and got a lightweight clamp to place on the switch to hold the button all of the way in. This would duplicate the normal position of the switch before you press the brake pedal. I then ran the test and no problems. When the clamp was released, replicating pressing the pedal I got the correct response. 

 

So I reinstalled the switch and pressed it in a few more "clicks" so the button would be fully pushed in. A quick test drive indicated the cruise was like new again with correct responses and dash lights responding for each cruise state. ...

 

Just for future reference... the way I adjust the switch is to push the ridges on the tube all the way into the bracket that holds the switch, making sure the button on the end is aligned properly with the brake pedal. Then pull up on the brake pedal with your hand until it bottoms out on the stop the brake pedal normally rests against. That will push the switch to the proper position in the bracket so it will operate as it should. I don't know what the FSM says about adjusting the switch but this way has always worked for me.

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