Update on Tire Size Problem
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Update on Tire Size Problem
Thought I would update everyone on the tire size problem I've encountered. I now have 26.6 size tires on the front and 27.7 size tires on the rear with a difference of 1 inch in tire diameter. This is right in the middle of the .5" to 1.5" window I was to be in. I thought this would fix the problem with the trac cont and ABS, but both lights still come on at exactly 31 MPH along with the warning to service both systems. I took the Tech II for a drive and monitored the wheel speed sensors and speedo operation. All wheel speeds are exactly the same while matching the vehicle speed, which, by the way, exactly matches the speedometer of the car. There are no codes in the ABS system. The tugging at the front brakes has stopped, at least for the few test trips I've made.
At this point am really confused, and, would like to figure it out. So far, I have been pretty lucky fixing things the correct way with some great help from everyone, however, this ones pretty strange and will not go away. Any other bits of insight would be greatly appreciated before I have to submit the dealership route.
Thanks,
Yellow '01
At this point am really confused, and, would like to figure it out. So far, I have been pretty lucky fixing things the correct way with some great help from everyone, however, this ones pretty strange and will not go away. Any other bits of insight would be greatly appreciated before I have to submit the dealership route.
Thanks,
Yellow '01
Melting Slicks
Joined: Nov 2009
Posts: 2,922
Likes: 219
From: West Branch, MI
This might sound like a strange suggestion but it might be worth a try. Have you put your stock size tires back on and the problem went away? I see you have tall rear tires as do I (I'm running a 325/45/17 M&H on the rear which are 28") and while I'm planning on some new taller front tires, I went for a drive with the 325/45's and the stock front tires (25.5" tall) and I did not get any error codes whatsoever. Mind you, I didn't go for a long ride, just a couple of miles, but no codes. If you have the stock tires and wheels still available to you, it might be worth a shot to see what happens.
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Will try the old ones
This might sound like a strange suggestion but it might be worth a try. Have you put your stock size tires back on and the problem went away? I see you have tall rear tires as do I (I'm running a 325/45/17 M&H on the rear which are 28") and while I'm planning on some new taller front tires, I went for a drive with the 325/45's and the stock front tires (25.5" tall) and I did not get any error codes whatsoever. Mind you, I didn't go for a long ride, just a couple of miles, but no codes. If you have the stock tires and wheels still available to you, it might be worth a shot to see what happens.
With my old set, I had no problems at all. I wanted to make a nice change in wheel style and fill the wheel wells up some. See attached pic. I was assured that this is a good idea as it is easy to override the system. Now its sounding like I'm going to have to fight through this problem as I am unable to find a cure. Guess I'll have to go back to the old wheels
Thanks for any advise, or, if you know anyone who went through this, please send them my way. I'll let you know if the old set still works. BTW this is a picture from last week, since then I have put on a larger rear tire that balances out the size difference a lot better and fulfills the requirement that 8VETTE7 recommended. It now has a 1" difference from front to back and looks great with no clearance issues.
Yellow '01
Last edited by Yellow '01; May 17, 2016 at 01:05 AM. Reason: More info
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SWPS tests good
If I had to guess what is going on with the ABS/AH/TC lights lit but no codes showing, I would suspect the SWPS. Common issue when it's getting ready to go bad. Symptoms are brakes being pulsed when they should not be and the lights that you have lit showing. Codes are often not set when codes are pulled with the engine off but key on because the system thinks it is simply correcting because of a driver initiated action. ie not a fault condition.
Next time you take the car for a drive and the lights illuminate, pull up the codes BEFORE you shut off the engine. You MAY see a TCS code such as C1281 or C1286 or C1287.
If you go the Stealership route for diagnosis expect a very large drain to your check book..........
Next time you take the car for a drive and the lights illuminate, pull up the codes BEFORE you shut off the engine. You MAY see a TCS code such as C1281 or C1286 or C1287.
If you go the Stealership route for diagnosis expect a very large drain to your check book..........
Great idea on the ST Wh pos sensor. I ran the test from lock to lock with the Tech II. Did it twice and it passes both times. My brakes do not pulse. In fact, they are really good, very smooth and firm. I did perform a fluid change as its a good idea to do that periodically.
I did perform a code check but after the engine was off. I will do it again before shutting down. May be a day or two as it been raining a lot here and I have a 400 foot gravel driveway.
Thanks for hanging in there with me on this
Yellow '01
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Yes, they are bigger and I really like the look. I did stay within the tire size difference parameters as 8VETTE7 suggested, in fact right in the middle. The old post was named Different tire size - problems. I am going to try the old tires and wheels to insure that the system is working properly, even though the car was working fine before this change.
Any other suggestions or ideas you have are greatly appreciated
Yellow '01
Drifting
Joined: Aug 2012
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I like the look, and was looking at going with taller tires myself......What sizes did you go with?.......Any clearance issues?.....Im assuming those are stock c6 wheels?......Did you use a spacer in the back?
Sorry for the thread hijack......
Sorry for the thread hijack......
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Thread Starter
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Welcome, not any hijacks here, we're all learning. I did not use spacers. The wheels are C6 takeoffs - great fit and look. The tires are: rear 275 40 19 @ 27.7 and the fronts are 245 45 18 at 26.7 . No clearance issues, just the ABS and Trac cont kicking on at 31 MPH.... I verified the wheel speed sensors with the Tech II on a road test and all where spot on as far as MPH with the speedo. If you know the exact way (button pushing sequence) to disable the traction control for a trip, drop me a note. BTW the picture above is from last week, since then I have put on a larger rear tire that balances out the size difference a lot better and fulfills the requirement that 8VETTE7 recommended. It now has a 1" difference from front to back and looks great with no clearance issues.
Yellow '01
Last edited by Yellow '01; May 17, 2016 at 01:02 AM. Reason: more info
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If you had a grounding issue with the EBCM you would have codes set because one of the other sensors could not communicate to the EBCM.
But if you want to chase grounds here are a couple links that will help with that:
http://forums.corvetteforum.com/c5-t...locations.html
http://forums.corvetteforum.com/c5-t...tion-long.html Post #1
But if you want to chase grounds here are a couple links that will help with that:
http://forums.corvetteforum.com/c5-t...locations.html
http://forums.corvetteforum.com/c5-t...tion-long.html Post #1
Great info on the links! This will help, and, that makes sense on the codes. I was reading about others having issues with the ABS and Trac control and had discovered ground issues as the problem. However, I am not getting anything that relates to ground problems. Never hurts to inspect them.
Are both the ABS and Trac Cont contained in the EBCM? If I remember right, the EBCM is located next to the fuse cluster on the passenger side floor board.
Thanks
Yellow '01
Melting Slicks
Joined: Feb 2001
Posts: 2,804
Likes: 358
From: Northville, MI
Since you have a Tech II did you go in and change the tire size for the speedometer? When I started autocrossing the Corvette (14 yrs ago) I had similar problems. Went from stock to 255/40x17/295/30x18 and thru codes. Changes the wheel sizes with EFILive and they have never returned. Each time I changes tires/wheels I go and reset the tire sizes.
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EBCM (Electronic Brake Controller Module) is located on the Frame below the alternator for mid model year 1998 through 2004 C5's. For the 97 through first half model year 1998 C5's the EBCM is mounted behind the differential at the back of the car.. Basically the EBCM is the anti lock brake controller.
The electronics that is in the passenger foot well behind the toe kick in an aluminum box is the BCM or Body Control Module. It manages and controls many systems related to the body. Example, when you press the door lock button, that grounds a circuit in the BCM which tells the BCM you want lock (or unlock) the door. The BCM sends signals to the door control module (DCM) that actually operates the door lock actuator. Another example is you press the lock button on your FOB. This transmits a signal to the RFA (Remote Function Actuator). The RFA decodes the FOB transmission and then sends a signal to the BCM over the serial data buss that tells the BCM that you want the door locked. The BCM then signals the DCM and indicates that the door is to be locked. The DCM then operates the door lock actuator. Other functions like the security system, rear hacth opening, getting TPMS info displayed in the DIC, opening and closing the windows and hundreds of other things are managed by the BCM. (Nothing is simple any more...
)
Active Handling (AH) and Traction Control System (TCS) both utilize the EBCM to control application of the brakes but under different conditions.
TCS utilizes input from the front and rear wheel speed sensors to determine that the rear wheels are spinning faster than the front wheels. The EBCM and PCM (Powertrain Control Module) work together to apply the rear brake(s) as needed to stop the wheel spin and the PCM backs out fuel and timing as needed. AH is best described by the following GM Video:
https://youtu.be/LWNR-tvvwFo
Hope this helps.....
The electronics that is in the passenger foot well behind the toe kick in an aluminum box is the BCM or Body Control Module. It manages and controls many systems related to the body. Example, when you press the door lock button, that grounds a circuit in the BCM which tells the BCM you want lock (or unlock) the door. The BCM sends signals to the door control module (DCM) that actually operates the door lock actuator. Another example is you press the lock button on your FOB. This transmits a signal to the RFA (Remote Function Actuator). The RFA decodes the FOB transmission and then sends a signal to the BCM over the serial data buss that tells the BCM that you want the door locked. The BCM then signals the DCM and indicates that the door is to be locked. The DCM then operates the door lock actuator. Other functions like the security system, rear hacth opening, getting TPMS info displayed in the DIC, opening and closing the windows and hundreds of other things are managed by the BCM. (Nothing is simple any more...
)Active Handling (AH) and Traction Control System (TCS) both utilize the EBCM to control application of the brakes but under different conditions.
TCS utilizes input from the front and rear wheel speed sensors to determine that the rear wheels are spinning faster than the front wheels. The EBCM and PCM (Powertrain Control Module) work together to apply the rear brake(s) as needed to stop the wheel spin and the PCM backs out fuel and timing as needed. AH is best described by the following GM Video:
https://youtu.be/LWNR-tvvwFo
Hope this helps.....
(on 2001). I actually ran solenoid operation checks on it two weeks ago and everything operated well and passed. So, in a nut shell, your saying that the BCM has nothing to do with the traction control and ABS. The video you provided shows what the EBCM does when traction limits are exceeded - good stuff. So does the AH and TCS reside in the EBCM? Or, are they separate and communicate with the EBCM through CAN? Is there any way to change the programming on the EBCM to accept tire size changes? If not, I will probably not be able to get the system to accept the tire size I want. What a bummer
Well, on the positive side I am better educated on this system, on the other hand I'm running out of options.I read about the swapping of the tires on this series of Vette in a book called C5 Corvette Builders Guide, by Thurn. In all the wheel and tire swapping they did, there was no mention of this issue and any resolutions if encountered. However, they did use tires that remained in the tire size family originally on the car when sizing up the wheels - they used 275 35 18 - 25.6" and 325 30 19 - 26.7". This remains in the diameter window you spoke of - 1.1 difference. I'm at 1.0 difference, but the tires are larger in diameter which is what is probably screwing up the system.
I did bolt the original wheels/tires back on today and will take it for a test drive when the ground around the shop firms up some - had
A LOT of rain lately. I'll get back to you if everything works OK and I think this will answer my questions.
Thanks
Yellow '01
Last edited by Yellow '01; May 17, 2016 at 08:47 PM. Reason: question
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Since you have a Tech II did you go in and change the tire size for the speedometer? When I started autocrossing the Corvette (14 yrs ago) I had similar problems. Went from stock to 255/40x17/295/30x18 and thru codes. Changes the wheel sizes with EFILive and they have never returned. Each time I changes tires/wheels I go and reset the tire sizes.
Hi, and I appreciate your response. I ran the calculation on those tires you mentioned, they are both 25". I can see why they threw codes, the window is .5 to 1.5 difference (learned from 8VETTE7) So, how did you get EFILive to fool the EBCM? I think all C5 folks would like to know the "secret". This would open the door for a lot of people wanting to do this. If you can give us the steps, step by little step, on how you accomplished this, it would be a big
Thanks
Yellow '01
Last edited by Yellow '01; May 17, 2016 at 08:22 PM.
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Hi, and, thought I would let you know that I do not know how to provide the link to the thread called Different tire size - problems
Its under the C5 tech section. Toward the bottom of this thread you will see that a lot has been learned on this subject. I am hoping that Gordy will respond with some EFI Live insight on this subject.
Any help you can provide to set the EBCM to the tire size I have would be great. I have: rear 275 40 19 at 27.7 and front 245 45 18 at 26.7 with a 1.0 difference
Thanks
Yellow '01
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Joined: Apr 2007
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From: South Western Ontario
Just to make it clear, the real difference between front to rear tires would be in revolutions/mile. It just happens that for tires around the stock diameters, the acceptable difference comes out to 0.5" to 1.5" and even then people have posted that they still had problems when pushing tire sizes to ether end of that range. All the ETCM knows is the difference in front to rear wheel speeds, not the ground speed.
The TechII should have a tire size menu, which basically adjusts the speedometer calculation numbers in the PCM so the speedometer reads correctly and the transmission shifts at the right speed. EFI Live and HPTuners can both also make this change.
I've never seen anything about putting in both front and rear tire sizes or anything about being able to adjust for the tire stagger the EBTCM expects on this forum before.
The TechII should have a tire size menu, which basically adjusts the speedometer calculation numbers in the PCM so the speedometer reads correctly and the transmission shifts at the right speed. EFI Live and HPTuners can both also make this change.
I've never seen anything about putting in both front and rear tire sizes or anything about being able to adjust for the tire stagger the EBTCM expects on this forum before.
Melting Slicks
Joined: Feb 2001
Posts: 2,804
Likes: 358
From: Northville, MI
Just to make it clear, the real difference between front to rear tires would be in revolutions/mile. It just happens that for tires around the stock diameters, the acceptable difference comes out to 0.5" to 1.5" and even then people have posted that they still had problems when pushing tire sizes to ether end of that range. All the ETCM knows is the difference in front to rear wheel speeds, not the ground speed.
The TechII should have a tire size menu, which basically adjusts the speedometer calculation numbers in the PCM so the speedometer reads correctly and the transmission shifts at the right speed. EFI Live and HPTuners can both also make this change.
I've never seen anything about putting in both front and rear tire sizes or anything about being able to adjust for the tire stagger the EBTCM expects on this forum before.
The TechII should have a tire size menu, which basically adjusts the speedometer calculation numbers in the PCM so the speedometer reads correctly and the transmission shifts at the right speed. EFI Live and HPTuners can both also make this change.
I've never seen anything about putting in both front and rear tire sizes or anything about being able to adjust for the tire stagger the EBTCM expects on this forum before.
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Joined: May 2015
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I don't know why it worked, last year I drove over 700 miles to Savanah, GA when my tow vehicles trans bit the dust, ran an autocross and Roebling Road (Nannies all off) and 700 miles return without any AH/TC issues. When I ran Hoosiers, I would occasionally have AH/TC kick on when driving on Expressway and would change lanes but never with street tires....even todays "200 TW" tires. Next week I will check with some of the tech center engineers who worked on the C5 project to see if they might know.
Thanks
Yellow '01
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Just to make it clear, the real difference between front to rear tires would be in revolutions/mile. It just happens that for tires around the stock diameters, the acceptable difference comes out to 0.5" to 1.5" and even then people have posted that they still had problems when pushing tire sizes to ether end of that range. All the ETCM knows is the difference in front to rear wheel speeds, not the ground speed.
The TechII should have a tire size menu, which basically adjusts the speedometer calculation numbers in the PCM so the speedometer reads correctly and the transmission shifts at the right speed. EFI Live and HPTuners can both also make this change.
I've never seen anything about putting in both front and rear tire sizes or anything about being able to adjust for the tire stagger the EBTCM expects on this forum before.
The TechII should have a tire size menu, which basically adjusts the speedometer calculation numbers in the PCM so the speedometer reads correctly and the transmission shifts at the right speed. EFI Live and HPTuners can both also make this change.
I've never seen anything about putting in both front and rear tire sizes or anything about being able to adjust for the tire stagger the EBTCM expects on this forum before.
I see what your saying. In reference to the Tech II - I have dug through what it offers pretty well and have not seen this adjustment. From what I've heard, the MDI does offer about .4 adjustment on the front and .7 on the rear. This is what our tech says at the DS
Thanks for the insight
Yellow '01