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Speedometer not working


Guest marcelosm

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Guest marcelosm

Hey everyone! So I recently purchased a red 88 reatta from a guy locally for a pretty decent price. Pretty much the only problem that I could find on the car was that the speedometer is not working. I've never owned a Buick before but on my Honda that would have been a simple fix. Little did I know that there wasn't as much info on this car on the net as there is for Honda. Regardless, I have decided that I want to fix it on my own without a mechanic.

My first stop was the battery and fuses. Now there was a fuse missing, number 17 on the fuse panel behind the little door. After taking off the rest of the side I found that I was also missing two fuses there, ecm ignition and ecm solenoid. Now I don't think that any of these have to do with the speedo but I will replace anyway.

Now I'm not too sure but from what I have read the regatta has 2 speed sensors; the abs wheel speed sensor and the transmission speed sensor. From my understanding the speedometer gets its reading from the transmission speed sensor located on the transaxle (still can't find the damn thing). Before replacing it I want to exhaust my resources.

The odometer does not work and the cruise control hasn't been tested because I can't drive around without my inspection stickers in my city. Anyone wanna give a nudge in the right direction?

Edited by marcelosm
changed year of car (typo) (see edit history)
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Guest marcelosm

Well I went ahead and pushed and held the test button andit cycled through all the different lights and they all seemed to be working. The speedometer is still stuck on zero mph tough. I'll go ahead and pull the codes up next

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It's most likely the vehicle speed sensor. This sensor is mounted on the automatic transmission. It has a two way electrical connector on it. They are available in The Reatta Store. You can see photos of it there.

ACDelco 213-2837 Professional Engine Speed Sensor

Another sign of a bad VSS is the torque converter will not lock. Also, you can go into diagnostics and read ED12 to see what MPH the ECM is seeing from the VSS.

Edited by Ronnie (see edit history)
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Guest marcelosm

Thank you for your help. I will go ahead and order another vss and replace it. The only question I have left is how to tell if the torque converter has locked up. Also (since I still want to check the diagnostics) what if I see that the ecm is receiving a speed from the vss?

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If you see a speed reading let us know and we will try to figure out what is going on. Be sure the VSS is plugged in and the connection is clean.

When the ECM is commanding the torque converter to lock you will see a triangle marked TCC light up when you are on the ECM screen in onboard diagnostics. This page will show you an example of what to look for. Keep in mind that the ECM will not lock the converter until the engine is fully warmed up.

I highly recommend you get to know all the pages the Reatta On-board Diagnostic System Booklet that I have been referring to really well. That booklet is your best friend when you are troubleshooting your Reatta.

You can also test to see if the converter is actually locked by getting the car up to 50+ MPH on level ground with the engine slightly accelerating, then (with your left foot) lightly apply the brake causing the converter to unlock. You should hear a change in the rpm of the engine. You can also see the RPM change when you look at the tach in the gages section of the CRT.

Edited by Ronnie (see edit history)
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Guest marcelosm

That diagnostic system is truly a marvelous thing. I wish other cars had a built in diagnostic system like this! I'll definitely read through it and take it for a drive. I'll post the results soon.

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Guest marcelosm

Okay so I thought it was going to be as easy as just replacing the sensor but I did the diagnostic and saw that the vss is indeed sensing a signal to the ecm. So I'm guessing that somewhere between the ecm and the panel lies the problem?

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OK, you are correct. If you are getting a MPH reading (ED12) then the VSS is sending a signal to the ECM.

The ECM doesn't send a signal directly to the instrument panel (IPC). The ECM sends a signal (pulses) to the BCM which in turn sends a signal to the IPC via a data line.

Next you should check to see if the BCM is getting a signal from the ECM. Go back into the onboard diagnostics and check BCM Data BD60 to see what the MPH reading is there. Report back here what you find.

Edited by Ronnie (see edit history)
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Guest marcelosm

The BCM was indeed not getting a signal from the ECM. It read 0 mph when I took it for a drive. So the problem lies between the ECM and the BCM?

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Sometimes disconnecting and cleaning/re-seating the connectors on the ECM and BCM correct this type of problem. That is what I would do next. They are both located behind/below the glovebox. The BCM can be seen in the photo below with all the wires coming out of it.

post-52331-143142651777_thumb.jpg

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May I also sugesst checking the BCM PROM code (BD99) as if it is incorrect it can adversely affect communication between the ECM and BCM in unpredictable ways The BCM generates the datastream that is fed to the IPC and thus it is critical the BCM is good, including the calibrator PROM chip.

As a reminder, 88 and 89 BCM (and ECM for that matter) PROMS are NOT interchangeable despite being nearly identical cars in most respects. I bring this up (again) due to an apparent rash of substitutions that have been made by those unfamiliar with the finer points of the electronics in the Reatta.

I got bit by this, as have a couple of other members here in the last 3 years. This is easy to mess up just by swapping in a spare BCM and not moving the chips from the old unit to the replacement. Apparently, that has been happening with cars serviced and then resold by the uninformed.

KDirk

Edited by KDirk (see edit history)
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Guest marcelosm

Well I opened up the glove compartment and found the BCM. I unplugged the negative battery terminal just in case and then went and unplugged all the cables going into the BCM. I gave em a good cleaning with electric contact cleaner and let them dry before putting them back on. I was hoping this would resolve the issue, but unfortunately it did not and the ED60 was still showing zeros. I'm not quite sure where to go from here.

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Guest marcelosm

Is there any way to check if the BCM is native to the car or, if it's a replacement, if it is the right year? Are there any markings to indicate the year of the BCM? What is the correct PROM code that should show up on the diagnostic screen?

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Guest marcelosm

Okay I think I found the problem. The PROM ID reads 3764 which is incorrect. I was reading up on another post here on the forum about the same thing. People replace the BCM but from another vintage. I'm guessing now all I have to do is find a known good BCM from my particular year and replace it?

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I don't have the pertinent information at my immediate disposal (not at home presently) but will add the following:

1. BCM (if original) has a sticker with a part number and service number. I do not own an 89 myself so have no reference for the correct original numbers. Easier to go by the connector color code, as each of the three plastic plug housings should match the color of the mating receptacle on the BCM. If these colors don't match it is likely to be the wrong module. I think (but don't hold me to it) that an 89 BCM should be black/black/red. When I get back home later I can verify this.

2. There should be a post here somewhere (I need to do a search) with PROM codes by year and application. Keep in mind that the code reported by diagnostics is a 4 digit number code. The chip itself will have a sticker bearing a 4 letter code. So, match either code (or both) to the list and you should be ok. If neither code matches what you have then it is the wrong chip. One caveat: sometimes a revised chip was issued resulting in more than one valid code for the same model and year. Check the list to be sure your code matches at least one shown for the year and module.

One last thought. This problem could be a bad ECM or BCM or wiring issue. The VSS signal goes to the ECM and is then retransmitted to the BCM on a dedicated circuit. If the output from the ECM or the corresponding input at the BCM is bad - or if the wire between those two points is open or shorted - the signal will be missing and thus never make it on to the IPC.

In fact, the more I think about it this seems the more likely scenario since only one parameter is missing (vehicle speed) but the rest of the composite data stream being read by the IPC is intact. That, and an incorrect PROM would almost certainly cause other problems beside the speedo issue.

The BCM "builds" a real time stream of data that it transmits to the IPC and CRTC (touchscreen controller module) from several discrete pieces of data: vehicle speed, engine speed, odometer, trip odometer, engine temperature, voltage, oil pressure, etc.

In simplistic terms, the corresponding displays then "pick off" the correct parameter from a list of data points to show in realtime to the driver either on the IPC or the touchscreen.

Now, if the whole data stream is lost you will have no display at all on the IPC other than the word "error". Conversely, if one particular piece of data is missing prior to being compiled by the BCM into the running datastream, the list will still be built and transmitted but with that missing value substitued with a default place holder (in the case of vehicle speed that would be "0") therefore giving you a display of 0 mph (or km/h as appropriate).

Sorry to be so long winded, but this seemed like a good opportunity to describe how this system works in some detail.

KDirk

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Ok, you did the leg work and posted while I was typing my opus above. The BCM may be ok (should be verified though) but the PROM can be changed independently. Another detail is that there are two PROMS inside the BCM. One is the chip we have been discussing. The second is a slightly smaller (24 pins vs. 28) chip that stores the odometer reading, the VIN and some other programming specific to your particular car. This latter chip MUST stay with the car whenever the BCM gets changed or your odometer reading and VIN will be wrong if reusing this chip from a different car's BCM.

In any case, the 28 pin PROM is socketed inside the BCM (concealed by a small aluminum cover with 4 screws) for easy replacement so once the correct one is found, it can be plugged in.

KDirk

Edited by KDirk (see edit history)
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Guest marcelosm

First off, thank you two so much for your help and quick responses. I doubted that I could find any help outside of archived posts from years back but you surprised me! I appreciate that you took the time to write out that explanation for me. I'm sure that this thread will be useful to somebody else in the future as well.

Now, my car is an 88 not an 89 so that might be something to take into consideration. I tried searching the forum for any posts making reference to the ED99 code for my vintage but only found that the correct PROM id for an 88 is 3534. Now its gotten a bit late and I can't exactly work well in the dark, though I have tried. I might have to wait till tomorrow to try and pull out the BCM and check what the sticker says and try and match it up.

I think I will follow that route first unless you think its better for me to try and figure out of the connection from the ECM to the BCM is good.

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Guest marcelosm
I don't have the pertinent information at my immediate disposal (not at home presently) but will add the following:

1. BCM (if original) has a sticker with a part number and service number. I do not own an 89 myself so have no reference for the correct original numbers. Easier to go by the connector color code, as each of the three plastic plug housings should match the color of the mating receptacle on the BCM. If these colors don't match it is likely to be the wrong module. I think (but don't hold me to it) that an 89 BCM should be black/black/red. When I get back home later I can verify this.

2. There should be a post here somewhere (I need to do a search) with PROM codes by year and application. Keep in mind that the code reported by diagnostics is a 4 digit number code. The chip itself will have a sticker bearing a 4 letter code. So, match either code (or both) to the list and you should be ok. If neither code matches what you have then it is the wrong chip. One caveat: sometimes a revised chip was issued resulting in more than one valid code for the same model and year. Check the list to be sure your code matches at least one shown for the year and module.

One last thought. This problem could be a bad ECM or BCM or wiring issue. The VSS signal goes to the ECM and is then retransmitted to the BCM on a dedicated circuit. If the output from the ECM or the corresponding input at the BCM is bad - or if the wire between those two points is open or shorted - the signal will be missing and thus never make it on to the IPC.

In fact, the more I think about it this seems the more likely scenario since only one parameter is missing (vehicle speed) but the rest of the composite data stream being read by the IPC is intact. That, and an incorrect PROM would almost certainly cause other problems beside the speedo issue.

The BCM "builds" a real time stream of data that it transmits to the IPC and CRTC (touchscreen controller module) from several discrete pieces of data: vehicle speed, engine speed, odometer, trip odometer, engine temperature, voltage, oil pressure, etc.

In simplistic terms, the corresponding displays then "pick off" the correct parameter from a list of data points to show in realtime to the driver either on the IPC or the touchscreen.

Now, if the whole data stream is lost you will have no display at all on the IPC other than the word "error". Conversely, if one particular piece of data is missing prior to being compiled by the BCM into the running datastream, the list will still be built and transmitted but with that missing value substitued with a default place holder (in the case of vehicle speed that would be "0") therefore giving you a display of 0 mph (or km/h as appropriate).

Sorry to be so long winded, but this seemed like a good opportunity to describe how this system works in some detail.

KDirk

Now that I think about it the BCM connectors were indeed black black red, but like you said, this was for an 89 not an 88 like my own. So that might indicate that the BCM was replaced with an 89 BCM which is causing my issues. I still need to pull it just to verify though. What I am trying to understand though is, does the whole BCM need to be changed if it is an 89 or just the prom?

Edited by marcelosm (see edit history)
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Ok, now I'm getting confused. Your original post stated you had an 89, is that correct; or is it an 88?

The basic BCM is the same for both 88 and 89. Functionality specific to each year is handled by a different PROM chip installed in the BCM for each year. Think of it as two identical computers running different operating systems.

So, if the BCM itself is good (undamaged and not malfunctioning internally) and is the correct model BCM (black/black/red connectors) then as it stands you might have the wrong PROM. But, without cross referencing the one that is installed to the known correct ID code, we can't yet say one way or the other. I will see if I can locate the correct code for a 1989 BCM PROM. Maybe someone else will post it before I can track it down.

If the PROM turns out to be correct then structured troubleshooting should be followed.

After eliminating the PROM as the cause (assuming it is correct) verify wiring for the VSS circuit between the ECM and BCM. If found to be open or shorted, correct the failure in this wire.

Ronnie's advice on making certain the contacts are clean and "making" correctly is also pertinent here, consider the contacts to be part of the wire.

Now, this is where a factory service manual is a must. If the wire & contacts check good then either the ECM is not retransmitting the VSS signal to the BCM or the BCM is not receiving/responding to it. That leads to determining which module is bad, and I'll need to review the 89 factory manual to offer more on that as otherwise I'm just shooting from the hip based on my recollections from working on my two 88's. More tomorrow after I've had a chance to do some reading.

KDirk

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Guest marcelosm

Ugh I must have mistyped when I first wrote my post. It is indeed an 88 and has been edited. What I imagine is that a BCM for an 89 was used as a replacement for this car but the prom was not switched over, causing the problems in functionality. Like I said, I will check the BCM and prom tomorrow as soon as I get the chance and post the results here. Again, thank you and good night!

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Ok. As it happens I'm burning the midnight oil too. Check your BCM PROM ID in diagnostics. It is under BCM > DATA > BD99. Correct ID for an 88 will read "9864". If you have another number then you have the wrong PROM. Note this is different from ED99, the ECM PROM ID which would could be a couple of different numbers for 88 as there was an early and late version chip. 3534 is the late revision, also known by letter code ANCX. If you have this PROM in your ECM, that is good as it corrects some minor problems of the early version.

So, this makes a bit more sense now. In 88, the VSS signal was routed first to the ECM which then filtered the signal and resent it to the BCM. In 89 this was reversed; VSS is sent first to the BCM and then onto the ECM.

The upshot of all this is that if you have an 89 BCM PROM installed, the BCM will not pickup the speed signal at all as the program on the 89 PROM is not looking for it on the same pin - or in the same signal format - as the 88 version. Therefore, it has no speed data to send to the cluster to display. If you have the wrong PROM, then that is almost certainly the entire problem.

Locating the correct PROM then becomes the next problem to tackle. Will cross that bridge after you report back with the BCM PROM ID.

KDirk

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Guest marcelosm

Okay I will do that as soon as I get out of work around 3pm central time. I feel rather stupid for mistyping the year of the car but I'm glad of is cleared up.

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Ugh I must have mistyped when I first wrote my post. It is indeed an 88 and has been edited. What I imagine is that a BCM for an 89 was used as a replacement for this car but the prom was not switched over, causing the problems in functionality. Like I said, I will check the BCM and prom tomorrow as soon as I get the chance and post the results here. Again, thank you and good night!

It would be helpful if you would add the model of your Reatta, (and any other relative information), to your signature line. It will make it easier for us to help answer your questions without repeatedly asking you about the specific model you own.

Click "Settings" in the menu at the top of this page and scroll down to "Edit Signature"

It's that easy!

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Guest marcelosm

Okay I just asked my girlfriend to check for me again (I had checked last night) and the bd99 is 3764 which is the incorrect prom id. So I guess we have found the solution to my problem, right?

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You found the cause. The solution is the correct PROM. Finding one is the trick. If all else fails, I can make one (I have the hardware to burn EPROMS and a supply of blank chips) however I don't have the black plastic carrier the chip is installed in to make it fit the socket inside the BCM. The old (wrong) chip can be removed from the carrier but is a delicate operation, as is the process of putting the new one into the carrier. Because it is old (25 years +/-) the plastic is easy to break.

The socket is a two piece design intended to prevent the chip from vibrating loose over time. It was the best solution available when these cars were new. These days there are much better one piece socket designs that don't need this carrier for position assurance.

KDirk

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Guest marcelosm

If thats the case then is there anyway I can send you my prom? That way you can use the plastic casing from mine? Of course I would pay you for your work kdirk. Or what do you think is best? Are there any suppliers that you know of?

Edited by marcelosm (see edit history)
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I don't mind doing it. I have already copied the PROMS for the ECM, BCM and CRTC on my 88 and have the file images archived. Yes, the contents of the chip can be copied just like a disk or sd card, just requires a special tool that hooks to a PC.

If you don't mind leaving the car inoperative (will not work with no PROM installed) for a bit I will gladly make a new one and transfer it into your carrier and send it back. Your other option is to check with the usual parts vendors listed in the Reatta Resources thread and see if any are able to supply you with a factory chip from an 88.

You might (but I would be surprised) be able to find a NOS one from a dealer, but that would probably be the most costly option - if one is even available.

If you want to have me make one up, PM me on here and I'll get you details.

KDirk

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Guest marcelosm

Give me till the end of the day to find one online and if I can't then I will pm you so I can have it in the mail by tomorrow. I don't need the car more, or rather can't, because I can't pass the state inspection with no speedometer. I'll pm you as soon as I decide what to do.

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  • 2 weeks later...
Guest marcelosm

post-102209-143142679368_thumb.jpg

Okay so I finally recived another 88 bcm that should plug in correctly and fix my problems right? Well no, not that easy. Either I got sent the wrong bcm or my car is not actually an 88 because the cables that come up from the ecm and plug into the front of the bcm do not fit. The small grooves are in different places. Also, the prom chips are not compatible. When I pull the one that was originally in the car off, the contacts are on the chip whereas the one I just bought has the contacts on the board. The one I just bought has a prom chip that says blue one the bottom whereas the other one says nothing. I will add photos so you can see. Are the wires incorrect as well or what? I'm kind of frustrated because it thought it was going to be as easy as replacing the bcm. The one I just bought has the brown connectors and the one in the car (looks much newer and say remanufactured) is the one with the black.

post-102209-143142679342_thumb.jpg

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That is definitely not the correct BCM. Not sure what application that fits but it isn't an 88 Reatta. Also, the unit you received has a different carrier (blue plastic piece) versus the black plastic one that would be correct for the 88 "E" platform (of which the Reatta is one model).

So, in short, what you have there won't work. To confirm your car is an 88, we need either the full VIN or if you look at the switches in your center console (forward of the shifter) you should have 5 buttons. These will be fog lights, trunk access, fuel access, glove box & lamp retract; 89 has only two buttons there, fog lamps and lamp retract. Fuel and trunk release are in the glove box on an 89 model. 90 & 91 are entirely different again.

KDirk

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Guest marcelosm

It is indeed an 88 based on what you told me about the buttons. So I guess I need to send it back to the guy who sold it to me (roger from Reatta parts). Stay tuned

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