1989 Body Module and PROM

[attaer]

Battery draining by itself. Interior lights turning on by themselves. Replaced the Body Module. Still drains. Mechanic suggests it may be the PROM's. Will any year Reatta PROM's work in an '89?? or is each proprietary to the year of the car. Is there an after market source for PROM's??? Any help will be greatly appreciated.

[D-a-n-i-e-l]

I would go with it is very unlikely to be your prom, but if you want to follow that reasoning. Just unplug the BCM and see if the problem still arises.

I would really check into bad doorhandle switches and bad door jam switches.

Also a 88 prom will not work in a 89, at least not very well. I do not remember the specifics but when I tried it it caused a couple issues.

[attaer]

Thanks D-a-n-i-e-l.

I appreciate you taking time to submit your valued comments. I may have access to 1990 PROM's from a wrecked Reatta I found at a Pick n Pull. If '90 PROM's would work in a '89 I would grab those in addition to the door handle/jam switches. Thanks again. Any comments from you or others regarding the PROM's would be greatly appreciated.

[Machiner 55]

Not too long ago I purchased an ECM w/MemCal (PROM) from a '90 Reatta. I assumed that the MemCal would work in my '89. Well, you know what happens when we assume. It didn't work at all. The car wouldn't even start. The ECM itself is interchangeable between the two model years but not the PROMs. So the seller, being the great guy that he is, agreed to send me just the PROM from an '88 if I sent back the PROM from the '90 ECM I'd purchased from him.

I installed the newly acquired PROM into my ECM and now all is right with the world. Kept the ’90 ECM as a spare.

That is my experience with trying to put a '90 PROM into an '88 Reatta. You could try it... it won't hurt anything, but it may just be a waste of time and money.

[D-a-n-i-e-l]

your best bet is to find a 89 and purchase the bcm complete.

All auto parts in Spanaway WA has one 89 and I am sure that the BCM is there, but The last time I was there was two months ago

[Ronnie]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: attaer</div><div class="ubbcode-body">Battery draining by itself. Interior lights turning on by themselves. Replaced the Body Module. Still drains. Mechanic suggests it may be the PROM's. Will any year Reatta PROM's work in an '89?? or is each proprietary to the year of the car. Is there an after market source for PROM's??? Any help will be greatly appreciated. </div></div>

Before buying anything why not find what is draining the battery?

Disconnect the battery cable. Connect one lead of a voltmeter to the battery cable and the other lead to the battery terminal. (I like an analog voltmeter set to the 12 volt DC range.) Disconnect the ECM and BCM to eliminate them from drawing current. They will normally have a small current draw.

Then start removing fuses, unplugging connectors, operating door switches etc. and disconnecting things until the voltage reading on the meter goes to zero. Start reconnecting things and when the voltmeter starts to read a voltage again you have found the source of what is draining your battery.

[Machiner 55]

OK... I kinda goofed here. In the original post "attaer" was refering to the BCM not the ECM. My Bad.

But... does the BCM also have a PROM inside of it?

[KDirk]

Ok, this will be a long post but for the sake of clarification here is some useful info:

The BCM does have an EPROM (often a one-time programmable chip, not UVEPROM or EEPROM), and it is different for each model year on the Reatta. 88 and 89 are likely the most similar in terms of the program content, but are NOT interchangeable as posted above.

1990 BCM prom is largely different from the previous two years mostly on account of the interior instrumentation changes, and 91 is different again due to changes in the headlamp/twilight control system and a few other issues. The ABS system change in 91 likely also factors into this.

Bear in mind that the BCM interacts heavily with nearly all the electrical systems and options/convenience features on the car. Thus, the change from the 88/89 touchscreen CRT/integrated radio setup to the 1990 conventional digital dash/climate head/stand alone radio setup alone is a BIG factor.

BCM also has a lot to do with supplying information to the IPC in the correct format, it does some translation between the ECM and the IPC to make sure the speed, tach and other readouts receive the correct data. Also has some bearing on the climate control functionality.

Point being, while the 88/89 BCM module itself is probably the same part, the prom gives it the proper "personality" for the model or year it is installed in. Not sure about a 90/91 BCM itself being interchangeable to the 88/89 but I'm inclined to say not likely, as there were so many changes to the car in 90.

To further confuse the issue, ECMs also have PROMS (or in GM speak MEM-CALs) that are usually different by model year, even when the ECM itself remains the same part.

In fact, many major modules (IPC, SIR-DERM, among others) have a PROM that contains the program code specific to that module's internal operation. Many have a microcontroller (MCU) that is a combination of a CPU with integrated ROM and/or (E)PROM space to hold program code for the module. Sometimes these coexist with an additional PROM in the same module.

There are also serial EEPROMS in some modules that store things like the odometer mileage, the vehicle option programming content, and crash/deployment data in the case of the DERM.

And you thought you learned everything you needed to know about PROMS in high school [chuckle]. Admittedly, that kind of prom was probably more interesting for reasons that will not be discussed here.

KDirk

[Machiner 55]

Thanks for chiming in with all that great info.

That's why I really like this board... all the great people posting great stuff.