upsetvette

Hello everyone,

Some might some might not remember the "Where to get a BCM replaced or fixed" thread from about a year ago. Well the car is back to try and kill me again. But different this time.

Replaced BMC with used unit. Pulled some strings and got my mileage back to the low numbers it was not the high mileage of the BCM I got. new keys yadda yadda yadda all has been good for about a year.

The Car: 92 Vette Auto Vin P (base) No mods 100% stock

The problem: Some times no start, Some times starts but in no set amount of time you get "SYS" and Security flashing. loss of digital gauges on the dash and throws a ARS light in the "CID" Scan the CCM/BCM and get code 41 ( loss of serial com) Scan ECM when code is up and ECM doesn't resopnd. Let it sit....... it starts now, connect to ECM and no codes. Sit there reading live data and then it cuts out and the code is set again.

With code active I can scan the ABS and I get code 72 serial data link if I go to live data and see I do see brake switch but no TPS ( IE brake switch info from BCM and TPS from ECU showing ECU is down, no info ) CCM throws code 41 and then a FEDS code since the ECU will not respond. I know that is a by product code. I spoke with a Vette master tech and he told me to check the Mcal ( chip ) in the ECM. I opened it up last night and was locked in. I removed the board from the chassie and no huge problems seen but this is with the naked eye after all. I remove and reinstall the chip and still no good. Code returns.

I start looking for a chip or even a ECU. O the pain. The BCM took a while to find replacement but this isn't looking any better. I did search some posts with some names like ECUdepot.com but since it's sunday I can not call them and they seem to have none in stock since the cost was $0 and core was the same. I want to see if they think they can repair or have replacement chip. The Mcal I feel is where the problem is since I can throw the code when runnning and the car is not effected. The M cal as I am told ( I do not know his for sure ) is where the BCM gets the info for things such as the gauges and fuel info.

I know I don't have a short in the "bus" since my HVAC head doesn't go down. It works when the code is active. I have a factory book and have run all the testes for ccm code 41 and all have passed. in short they are check for connect to ECM from the BCM ( broken wires ) check for short to ground and bat+ and the "wiggle test" that turned in to the "Beat the ECM test" it ALMOST seemed that the beat the ECM test provoked it and with the drop out of data from the ECM when code is active I feel I am on the right track but I have been beat down by this very car before and want to be sure. I have gotten the code just sitting there and when active all wires still test good.

I don't know if I should:

1) send ECM out for repair
2) try to get replacement Mcal
3) replace ECM with a used unit ( I cant seem to find a Mcal alone and seems other chips piggy back that chip. That I am not 100% on )
4) burn the thing to the ground while making a Utube vid and tell the owner the dog took the car for a joy ride.

I am open to ideas let me know what you think

Again thanks for the help.

Bill M

94z07fx3

5) http://www.gordonkillebrew.com/

If you don't find an answer here, maybe a phone consult is in order.

0KEN W ANDERSON

Try GM AUTO COMPUTERS (below in tuning). We repair CCM's also & guarantee for a year plus program the correct mileage.

jaa1992

Not sure where you are - if you are in greater Atlanata area I could loan you my spare ECM for a 92 6spd while yours gets rebuilt. It would at least give you something to test with.

Jim Martley2

Same offer here if you are in the Albany, NY area!!

upsetvette

Thanks for the offers. I am located in NY on long Island. Going to make some call today and send out the ECM for repair. I cant find a chip that is not a piggy back also think it will be best to have the ECM tested.....

Thanks
Bill

Jamesnns

Subscribed.
Pm sent


Me too....damned code 41!
91, L98 stock.
Mine is "SES" on DIC, code 41, horrible running car.
Restart car, clears code, car runs good.
Intermittant.
No "Sys" or security light flashing.
No ARS
HVAC head doen't go down

read your post
"Where to get a BCM replaced or fixed"
My chimes are intermittant, or barley there " key in, door open...etc" is this an indicator?

What result did you have from a year ago, the posts stopped?

At normal start, scanner indicated all parameters are good.
can't run diag tests becuas it's so intermittant, and when code is set, whole link goes down.

I feel your pain.

upsetvette

Finished off that other post for the searches. Not joking took almost a year to find the right BCM.

I am going to make some call right now and put the car down for a bit while I send out the ECM and have it tested.

I did reply to the PM but will post a bit here for the fuiture search.

Is the HVAC head blinking the "off" button? Will the ABS (ASR) respond to the scanner and can you see live data? If so can you see a TPS reading when you press it down? Scan the ECM for code. What are the code even if you think it's not relevent it will help in understand the thinking of the code and that will lead you to the fault.

in short if the whole bus goes down and no com from the CCM, ECM, HVAC, ABS would be a open in serial bus, Short to ground in bus or short to bat +

I don't loose the whole bus just the info from the ECM. Since the ECM doesn't repond to the BCM's request in the allowed 600ms the BMC throws a FEDS fuel shut down code. Since the ECM is off line it never shuts down.

I would lean more to a bad Mcal or ECM for your car and same for mine. Samne but bad in differnt ways. It seems your timing and fuel are effected but mine are not but both are stopping the info flow and this make code 41 come up.

hope this helps
thanks
Bill

upsetvette

I wish I had a answer to post but I don't. I went with a "Reman" ecu for a vendor I will leave un-named. Was sent with out E-Prom ( where my problem is ) and when installed key on the roof of the car the Air inj pump is running and I have a ASR light on. This isn't good. No crank no start. O boy !! pull the ECU and it's SMOKING. I was pissed to say the least. Find a blown fuse for ECU memory and some others telling me it was putting power through the bus system. junk and crap hopeing that nothing bad happened to the BCM or other modules in the car.

Called and shipped back for a refund and they did the right thing and sent a full refund, this is why I didn't come back and flame them but in the same if I wanted poorly rebuilt crap I would have went to programa or napa for one. Thought a GM based repair shop could help but no.

N E WAY out of fustration I placed it to the side as I have many other projects and jobs to attent to and now getting up the courage and free time to start and TRY to find a answer for this. I know a few people contated me on the side via PM with the same problem. Trust me when I get a good answer I will let you all know.

For now looking for a used but good ECU that I can get with the M-Cal and hope all will be fine. After talking to a few friends in the local area that do nothing but vette repair they said what I was thinking was correct that it does have a problem with the M-Cal or the board it self. To the naked eye I don't see a short or burn but that doesn't mean much.

Will keep you all posted as the pain goes on.

Best Wishes
Bill

jaa1992

Call vette2vette and see if they have a used ECM with an auto memcal.
Someone else had thier ECM sent out to a place with blue in thier name - do a search.
The 92 ECM is scarcer than Hens teeth.

Good luck!

rinosaur

I thought 92-95 had the same code list, 41 is ignition control circuit?

corvette95

Serial data problem ar not diagnosed like other electrical problem, hence the serial data link. Its complicated if you dont really understand the entire data system. I replied to your prior thread. Couple of questions, why not buy a new not used unit? But better question, why not take it to a real corvette shop? I lot of people (including myself) that really knows how to work the data circuit keeps quiet because (not accusing) most threads involving ccm are people trying to tamper with mileage, just the way it is. Serial data is like a fax line, not 12 volts, image sending a fax and someone picks up a phone extension while the fax extension is sending data, even the click from picking up and hanging up the phone will ruin the fax, it only takes a little "static" on the line to throw everything off, but the wires can still test and ohm good. Thats just the start, spend a little cash and take it in. I know you are not local to me, but a good shop could have it baack to you in a day. Its a Corvette, drop a few bucks and get on the road. BTW forget the used ccm, get a new one, dont worry about setting the mileage. Just my opinion. I am trying to help to please no flaming.

upsetvette

I know your only trying to help. With no background from me I can see why you would say this. I am a experanced tech (over 15 years) and work on MBZ, Bently, Ferrari ect all day at my 9-5 ( really 8-6) job. Not trying to brag but I work on much more complex cars ever day. If you go back and read my posts you can see I'm a bit more advanced then your average bear the local Vette shops will not touch it. They agree with me that I am correct in my thinking about the M-cal but they like I can not find one.

I will make a call that someone in the for sale area made to a dealer but as far as I know the ECM is NLA from GM and all that are rebuild do not come with a M-Cal ( where the problem lies ) so that kinda leaves me where I am now.

I will call Vette to Vette. I have spoken with them before SUPER nice guy. Thats a good idea.


Just to direct answer the questions.
why not buy a new not used unit? But better question, why not take it to a real corvette shop?

New CCM and BCM has stopped a LOOOOOONG time ago from GM Used/rebuilt is the only answer. BTW CCM is not where the problem lies. Please go back and see older posting about the com only dropping on the ECM side. the old post about the CCM replacement was resolved with a used unit. I know what you mean about the mileage. I have 60K got one with over 170K and paid like a baby seal getting clubed to get it right. I did not want a OD sticker in the door jam.

I lot of people (including myself) that really knows how to work the data circuit keeps quiet because (not accusing) most threads involving ccm are people trying to tamper with mileage, just the way it is.

I know and understand. But also then you should see that the problem I am dealing with is not in the CCM it's in the ECM's lack of a responce to the CCM.

Serial data is like a fax line, not 12 volts, image sending a fax and someone picks up a phone extension while the fax extension is sending data, even the click from picking up and hanging up the phone will ruin the fax, it only takes a little "static" on the line to throw everything off, but the wires can still test and ohm good.


Yup did all of that. Isn't a short or open. Good contacts. Closed up the contacts in the ECM and CCM side to insure "Clean" signal.

Thats just the start, spend a little cash and take it in. I know you are not local to me, but a good shop could have it baack to you in a day.

They turned me away knowing it's just going to sit till parts are found. Why sit there not earning when it can sit in the driveway? It's a customer (Firends) car so he is already paying. I offered to dump it on someone elses plate but it's a trust thing. He trusts me. Not them ( Right fully so he has been abused by the so called Vette shops in this area. O I would love it to be someone elses problem

BTW forget the used ccm,

Again cant buy a new one so........

get a new one, dont worry about setting the mileage. Just my opinion. I am trying to help to please no flaming.

No flaming I know your just trying to help. We are all adults here just some that cry them self to sleep woundering when will I be able to return this car. It's a shame it's a very nice car. White on white leather. Well cared for. lot of cash spent to keep it right and it just bites back.


thanks for the help
Will call V2V now and see.
Bill

corvette95

Call me (now is good) at 205 276 1914 and I will tell you how to fix it. Chris

upsetvette

Thanks Chris

I'll post my finding later in the week or by next week

TY
Bill

corvette95

You're welcome!

upsetvette

Update

With some personal things going on and very little free time I have been hard pressed to find the free time to move foward with this. But I wanted to follow up since so many have contacted me on the side and so much help from the members I feel it's the best I can do. I ended up bring the car to my work where I will have the time to work on it. With it being a bit slow this is the time to deal with this.

After speaking with Chris (corvette95) he set me off on a path to find the problem. I am getting there. I did the pin point test and all have passed. Looking in to the dash harness now. Don't worry I'll post findings as I get to the end of this problem.

To all that have helped, thank you so much.
Bill

upsetvette

Hello all.

Well in the past month I have been able to work on it in between jobs to see what is going on. I have removed the dash pad, HVAC ducts, gotten to the main harness where splice S222 is located. Tape is in good shape and all contact are clean. Short of redoing the splice and running a new set of wires to the ECM I have done what I could there.
Performed testing across the splice with no change when moved around. Showing a good contact in the splice.

I Did the wiggle and pull test and can not make it happen. I have removed the pins (F12 & E13 tan serial data lines at the CCM/BCM) to insure they were closed and good contact. I have tugged, pulled slapped and all that I could think of to provoke a contact problem and no good. Both at the BCM and the splice. Same for ECM. I am leaning to the ECM is where the problem lies. Inside the M-Cal or the board it self. Can anybody direct me to a place that can do actual testing of the unit. I do not want to just replace it as so far I can not find a ECM with a M-Cal installed ( I do not want to use mine as this is where I feel the problem is. ) any help would be wounderful.

Thanks for all the help
Bill

upsetvette

Let me start with a big THANK YOU!! to all that helped me with this.



So it turned out to be the ECM. I was able to find a rebuild by Delco ecm at a yard. Plug and play all was fine. A lot of driving with the dash pad off and then put it all togeather. Drive it some more and all is well.

I had a feeling from the start that it was the ECM but I am gun shy since I have tried others with no luck. The problem could lie in the M-Cal ( chip in the ECU ) but I was able to find a M-Cal that matched the partss and options I had. Also many shaddy "Rebuilt" and "Tested" units out there. I went with a cost effective shot based on that I could not find a problem in the system at any other point.

I hope this helps some others that might be in the fight. The owner is going to sell the car and now looking for another. I wanto to get away from the Opti spark system and he is now looking for a newer one but a C4. I would like him to get a ZR-1

So again Thanks for all the help. He is happy motoring down the road as I type. I just got a min and wanted to post the fix!!

XR_Strider_GuY

Firstly apologies for the thread mining. But I have had a similar problem with my 1990 since I bought the car. It was one of those work in progress projects. Sorry for the long winded reply.

Here are the previous symptoms
From a battery reset I get a C41 when you ground A and G on the ALDL connector. However, when you grounded pin A and B I could get 12, 12, 12 forever indicating the ECM itself was fine. The car would start and run previously, but occasionally the idle will fluctuate and sometimes it would be hard to start (could be injectors as I have the original ones in there). Also the instantaneous fuel usage will occasionally work but more often than not will not work.

A good friend of the forums (Rodj) was kind enough to help diagnose the problem a year back by testing my car with another ECU but using my EPROM. He also confirmed that a scanner did not work to retrieve data from the ALDL connector. Confirmed exactly the same thing happened. The missing link would be to test with another EPROM but between us we did not have another suitable for my 1990.

Now
Recently the car has began to cutout, firstly after 10minutes of driving but more recently its cutting out more frequent i.e. 5 minutes after warmup. Upon cutout I tested the computer by grounding A and B on the ALDL connector and every so often I am unable to get a 12 12 12 confirmation. I am currently out ruling injector shutdown and/or distributor issues as that will not trigger a non 12 12 12 confirmation.

I narrowed it down to the ECM randomly not getting power on pin 17 the green connector. This explains why when it cuts out my speedo does not work.

Anyways I am waiting for a 2nd hand ECM with EPROM that has supposedly been tested to confirm its 100% working. I am hoping this sorts out A. the random cutout and B. the ECM/CCM communication.