ABS pulsation felt in brake pedal
07-13-2014, 08:09 AM
#61
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The STAR connectors are just bridges that connect together all the modules that are linked to them. They are troubleshooting devices that allow us to isolate circuits to help in the process of identifying the source of a problem.
If I'm not mistaken, Bill asked you to verify that you had point-to-point continuity in the COMM link between the BCM and the EBTCM. To do that you need to check from the COMM "BCM connector pin" to the corresponding "EBTCM connector pin", with the STAR1 closed, otherwise the link would be broken midway. If the link is fine you should get 0 ohm from end to end, or very close to that.
What I meant by "legs" is that if you open the STAR1 connector, the COMM link between the BCM and the EBTCM gets separated in 2 segments or legs: one between the BCM and the STAR1 connector and another one between the STAR1 connector and the EBTCM. Since the STAR1 connector is linking 9 circuits together and you want to make sure the COMM link between the BCM and the EBTCM is not grounded, it is best to isolate it from the other circuits so its reading to ground doesn't get affected by their interaction. That's why I said to open the STAR1 connector and then check both segments of the COMM link for infinity with respect to ground.
By the way, the COMM wire from the EBTCM is light blue (STAR1 pin E), but the COMM wire from the BCM is light green (STAR1 pin M).
If I'm not mistaken, Bill asked you to verify that you had point-to-point continuity in the COMM link between the BCM and the EBTCM. To do that you need to check from the COMM "BCM connector pin" to the corresponding "EBTCM connector pin", with the STAR1 closed, otherwise the link would be broken midway. If the link is fine you should get 0 ohm from end to end, or very close to that.
What I meant by "legs" is that if you open the STAR1 connector, the COMM link between the BCM and the EBTCM gets separated in 2 segments or legs: one between the BCM and the STAR1 connector and another one between the STAR1 connector and the EBTCM. Since the STAR1 connector is linking 9 circuits together and you want to make sure the COMM link between the BCM and the EBTCM is not grounded, it is best to isolate it from the other circuits so its reading to ground doesn't get affected by their interaction. That's why I said to open the STAR1 connector and then check both segments of the COMM link for infinity with respect to ground.
By the way, the COMM wire from the EBTCM is light blue (STAR1 pin E), but the COMM wire from the BCM is light green (STAR1 pin M).
100% correct!!
:iagree :
You should be taking a reading from the EBTCM COMMS wire in the main EBTCM Connector to the BCM COMMS wire in the BCM Connector with the STAR Buss cap installed in the STAR connector.
You need to verify that you have a good COMMs circuit between the EBTCM ALLLLLLLLLLLLL the way to the BCM connector.
You can also measure the BCM comms pin to ground and should also see a similar resistance to chassis ground to verify that the BCM Comms pin is a good circuit.
Bill
:iagree :You should be taking a reading from the EBTCM COMMS wire in the main EBTCM Connector to the BCM COMMS wire in the BCM Connector with the STAR Buss cap installed in the STAR connector.
You need to verify that you have a good COMMs circuit between the EBTCM ALLLLLLLLLLLLL the way to the BCM connector.
You can also measure the BCM comms pin to ground and should also see a similar resistance to chassis ground to verify that the BCM Comms pin is a good circuit.
Bill
07-14-2014, 11:16 AM
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Here is the update.
With the star 1 bridge connector removed, I do not show a path to ground on either leg. With the bridge in, I show perfect continuity on the COMM wire between the BCM and the EBTCM. This puts that test to bed in my mind.
Now I have a question that is brought to mind after re-reading the symptoms of the P1571 code. Here is a cut and paste from the book:
The following conditions can cause this concern:
An open in the requested torque circuit.
An short to ground or voltage in the requested torque circuit.
A wiring problem, terminal corrosion, or poor connection in the requested torque circuit.
A communication frequency problem.
A communication duty cycle problem.
The PCM is not receiving information from the EBCM.
Loose or corroded EBCM ground or PCM ground.
I have underlined the last two because they mention the PCM. I'm wondering if I should do a similar check with the PCM COMM wire? When I was repairing the vacuum line to make my A/C vents work properly, I had the access cover off to the PCM and I could see the connector. It was not overly corroded or anything that alarmed me at the time, but I was tempted to disconnect the connector and clean it up. I was afraid to mess with it as I didn't want to possibly cause more gremlins by disturbing it. Now I'm having second thoughts.
The alternative is to wait till my EBTCM get back in a few days, and install it and see what codes I get. What do you think?
With the star 1 bridge connector removed, I do not show a path to ground on either leg. With the bridge in, I show perfect continuity on the COMM wire between the BCM and the EBTCM. This puts that test to bed in my mind.
Now I have a question that is brought to mind after re-reading the symptoms of the P1571 code. Here is a cut and paste from the book:
The following conditions can cause this concern:
An open in the requested torque circuit.
An short to ground or voltage in the requested torque circuit.
A wiring problem, terminal corrosion, or poor connection in the requested torque circuit.
A communication frequency problem.
A communication duty cycle problem.
The PCM is not receiving information from the EBCM.
Loose or corroded EBCM ground or PCM ground.
I have underlined the last two because they mention the PCM. I'm wondering if I should do a similar check with the PCM COMM wire? When I was repairing the vacuum line to make my A/C vents work properly, I had the access cover off to the PCM and I could see the connector. It was not overly corroded or anything that alarmed me at the time, but I was tempted to disconnect the connector and clean it up. I was afraid to mess with it as I didn't want to possibly cause more gremlins by disturbing it. Now I'm having second thoughts.
The alternative is to wait till my EBTCM get back in a few days, and install it and see what codes I get. What do you think?
07-14-2014, 07:41 PM
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WAIT and install the repaired EBTCM and see what you have then. Dont loose sleep over what you already know is most likely defective. 
Good job on the resistance checks.
Bill
07-16-2014, 04:57 PM
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Quick update. I called the tech at ASAP Speedo to get a feel for if they thought they would be able to repair the module or not. He said he was confident they would, and that their finding are only 2% of them are not repairable.
He said mine was currently apart on the bench with two others in the same boat. In other words the customary new relay doesn't fix them. i asked if he had a game plan moving forward, and he said he felt like there possibly is a lazy solonoid acting up. Saying that they bench test ok, but don't work once on the vehicle. He also said that they are expanding their testing capabilities specific to the C5, so they could offer a more thorough test to verify the modules are indeed functional once shipped back to the customer.
Hope mine is not one of the 2% with a bad brain.
To add to my dilema, I'm still not convinced the set of codes I'm getting are a result of a bad ECTBM. I really wish I had a known good one I could swap in to verify.
He said mine was currently apart on the bench with two others in the same boat. In other words the customary new relay doesn't fix them. i asked if he had a game plan moving forward, and he said he felt like there possibly is a lazy solonoid acting up. Saying that they bench test ok, but don't work once on the vehicle. He also said that they are expanding their testing capabilities specific to the C5, so they could offer a more thorough test to verify the modules are indeed functional once shipped back to the customer.
Hope mine is not one of the 2% with a bad brain.
To add to my dilema, I'm still not convinced the set of codes I'm getting are a result of a bad ECTBM. I really wish I had a known good one I could swap in to verify.
07-27-2014, 11:16 AM
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Sorry, had company so I didn't get to work on the vette.
Another member here sent me a spare module to swap in so I could see if my codes changed. They did! In fact they all went away. The console switch that turns on/off A/H even works now.
This proves my module was indeed bad. I called the tech working on my module, and he said that they rebuilt every rebuildable part inside, all that is left that could be bad is the chip set. They mailed it back to me, and as soon as I get it, I will install and see what happens. If I get the codes again, I will purchase a new module.
Another member here sent me a spare module to swap in so I could see if my codes changed. They did! In fact they all went away. The console switch that turns on/off A/H even works now.
This proves my module was indeed bad. I called the tech working on my module, and he said that they rebuilt every rebuildable part inside, all that is left that could be bad is the chip set. They mailed it back to me, and as soon as I get it, I will install and see what happens. If I get the codes again, I will purchase a new module.
08-08-2014, 07:38 AM
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Update:
The repaired unit does not work. It is toast. I have purchased a used module from the classifieds on here. Hope to have it installed this weekend.
The repaired unit does not work. It is toast. I have purchased a used module from the classifieds on here. Hope to have it installed this weekend.
08-08-2014, 10:03 AM
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08-08-2014, 11:19 AM
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They paid shipping back to me twice, and I was very impressed with their customer service. I knew going into the deal that my chipset was probably the culprit. I thought it was worth a try. I'm very satisfied they did their best to repair it.
08-10-2014, 02:07 PM
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Installed my new but used EBCM this AM. It works like it is supposed to. All those ABS codes went away. Now I have a 10-PCM P0171 H that popped up after a long drive. Also the check engine light just came on. Hope this car isn't going to make me start hating C5's.
08-10-2014, 02:56 PM
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Several possibilities. Leak in the air plumbing after the MAF, leak in the PCV lines, loose gas cap or bad seal on the gas cap.
Look for cracks in the plumbing of the air tubes from the MAF to the TB. Also loose clamps at connectors. A car the age of yours may well have rotted or cracked lines in the PCV system. Examine them carefully Check your gas cap.
if you don't like challenges, you may well start hating C5's. They can have their share and then some of issues:
http://forums.corvetteforum.com/c5-t...must-read.html
Look for cracks in the plumbing of the air tubes from the MAF to the TB. Also loose clamps at connectors. A car the age of yours may well have rotted or cracked lines in the PCV system. Examine them carefully Check your gas cap.
if you don't like challenges, you may well start hating C5's. They can have their share and then some of issues:
http://forums.corvetteforum.com/c5-t...must-read.html
I agree,,, Your getting UNMETERED air from somewhere.
DTC P0171 or P0174 Fuel Trim System Lean
Vacuun leak or air ducting between MAF and TB
PCV lines are well known to cause this too
BC
08-10-2014, 03:44 PM
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I'm up for the challenge. I was just hoping it was over at least for a couple of weeks. I'll check out the hoses as suggested. Could just have knocked something loose since I was messing with the EBCM about 1000 times. Glad that part is over.
I just re-pulled codes and got another set.
40-BCM B0502 H C
40-BCM B0507 H C
40-BCM B2482 H C
I had a front rt turn signal bulb out. I knew about it, but after changing it out, the codes still come back. The RT rear parking lamp is also out. The one on the rear quarter panel behind the tire.
I can't get my hand up in there to pull out the bulb. I have aftermarket exhaust, and the pipe is in the way. Any other access through the trunk? Could this be causing the codes?
Probably not since my book says it is some kind of relay. Have to track that down some more. I didn't understand the abbreviations used. Going to look those up also. RH DRL???
I just re-pulled codes and got another set.
40-BCM B0502 H C
40-BCM B0507 H C
40-BCM B2482 H C
I had a front rt turn signal bulb out. I knew about it, but after changing it out, the codes still come back. The RT rear parking lamp is also out. The one on the rear quarter panel behind the tire.
I can't get my hand up in there to pull out the bulb. I have aftermarket exhaust, and the pipe is in the way. Any other access through the trunk? Could this be causing the codes?
Probably not since my book says it is some kind of relay. Have to track that down some more. I didn't understand the abbreviations used. Going to look those up also. RH DRL???
08-10-2014, 04:30 PM
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Take the outside right tail light out. You can access the light bulb from there. The motor for the antenna on a VERT makes it a challenge unless you have long thin arms and can reach under the motor with your left hand. I just did this on my vert to install led bulbs so I know it can be done. My arms are the only skinny part of me.......... 
Thanks for the tip. I just looked it up in the manual, and saw that was the access. My arms are skinny...
Going to check the DRL's in the IP electrical center. Maybe I bumped them when I was inside troubleshooting the EBCM wiring.
Thanks.
08-11-2014, 08:04 PM
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update:
After changing all the bad bulbs and still getting the same 3 BCM codes of:
40-BCM B0502 H C
40-BCM B0507 H C
40-BCM B2482 H C
I decided to start in on the troubleshooting. It went very fast. I found the fuse to the DRL had been pulled. DUH!
Put in the spare fuse and those three codes are gone. I currently am code free for the first time since I owned the ol girl. What a good feeling. I know the code 10-PCM P0171 may pop back up after a long drive, but perhaps not. I tightened up some air inlet hose clamps after the MAF. We shall see. Now I can concentrate on getting the interior up to par. The leather seats could use some new foam on the D.S. and it does rock. You know; all the usual stuff!
40-BCM B0502 H C
40-BCM B0507 H C
40-BCM B2482 H C
I decided to start in on the troubleshooting. It went very fast. I found the fuse to the DRL had been pulled. DUH!
Put in the spare fuse and those three codes are gone. I currently am code free for the first time since I owned the ol girl. What a good feeling. I know the code 10-PCM P0171 may pop back up after a long drive, but perhaps not. I tightened up some air inlet hose clamps after the MAF. We shall see. Now I can concentrate on getting the interior up to par. The leather seats could use some new foam on the D.S. and it does rock. You know; all the usual stuff!
08-11-2014, 09:48 PM
#77
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After changing all the bad bulbs and still getting the same 3 BCM codes of:
40-BCM B0502 H C
40-BCM B0507 H C
40-BCM B2482 H C
I decided to start in on the troubleshooting. It went very fast. I found the fuse to the DRL had been pulled. DUH!
Put in the spare fuse and those three codes are gone. I currently am code free for the first time since I owned the ol girl. What a good feeling. I know the code 10-PCM P0171 may pop back up after a long drive, but perhaps not. I tightened up some air inlet hose clamps after the MAF. We shall see. Now I can concentrate on getting the interior up to par. The leather seats could use some new foam on the D.S. and it does rock. You know; all the usual stuff!
40-BCM B0502 H C
40-BCM B0507 H C
40-BCM B2482 H C
I decided to start in on the troubleshooting. It went very fast. I found the fuse to the DRL had been pulled. DUH!
Put in the spare fuse and those three codes are gone. I currently am code free for the first time since I owned the ol girl. What a good feeling. I know the code 10-PCM P0171 may pop back up after a long drive, but perhaps not. I tightened up some air inlet hose clamps after the MAF. We shall see. Now I can concentrate on getting the interior up to par. The leather seats could use some new foam on the D.S. and it does rock. You know; all the usual stuff!
I am currently code free again too - my loose fuse #5 had been jammed in there tight (with an extra set of tabs) and things are working great. New fuse box is on its way... fingers crossed!
08-11-2014, 10:16 PM
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