Computer Communications and ECM

[Guest SwiftBuicks]

Well, I determined that there's something amiss between the ECM and the BCM in my '89 Riv. Between the error code B334, the warning message <span style="font-weight: bold">COMPUTER COMMUNICATION PROBLEM DETECTED some vehicle function may exhibit degrading performance</span> and the <span style="font-weight: bold">NO ECM DATA</span> output, I have no doubt that I should check the wiring connections between the two. Since I have put in a new BCM, I will concentrate on the ECM. First of all, I have to find it.

[KDirk]

Just occurred to me-

Check and make sure the cover cap is installed properly on the ALDL (diagnostics) port located below the driver's side knee bolster. I think the cap has a shunt in it that ties the two sides of the serial data line together.

This is important in that if you have an open somewhere in the serial data line, the signals can still travel back around the other direction and get to their destination. This is why all modules have two connections to the serial line. With the cap not installed, this redundancy feature is defeated.

That said, if you have more than one open in the data line, or a failed ECM/BCM, the shunt cap will not help. And, if you do have a wiring problem it still needs to be located and corrected.

KDirk

[reattadudes]

the ECM (or PCM , for Powertrain Control Module, in GM-speak) is not fun to get out of the car.

take out the glove box, and the PCM will be in a vertical position, right next to the A/C controller, on the right side of the glove box opening; just look for the arm that conencts the A/C controller, and the PCM is right next to it. there are some 7MM/#15 Torx screws at odd angles that will need to be removed on the top part, as well as loosening a few 10MM nuts that secure the unit to the car.

on the bottom, remove the black hush panel (contains the courtesy lamp in the right footwell). every car is different, but you might be best off to pull back the carpeting (not a fun job) to access the bottom of the PCM, and more importantly, the plugs. the plugs can be especailly difficult, as many times they are stuck, and are very hard to release. you won't have much room to work, either.

I still very strongly suggest a trip to an electrical shop, rather than continuing on this fishing expedition. just trying to unplug the PCM can cause problems with wires close by, and the A/C controller vacuum lines.

that computer communication problem message you are receiving could very well be just a bad wire or corroded plug under the hood. as I mentioned before, an electrical shop could easily diagnose this problem. in the many years I've been dealing with Reattas, I've found the 99% of the time it's something really small, not something big.

Mike

buickreattaparts.com

[Guest SwiftBuicks]

Reattadudes, I don't believe we have the same vehicles. I've been behind the glove box and couldn't see the ECM. I don't have a Reatta but a Riv. Perhaps when I return to Ma., I'll go to an electrical shop, but for now in rural Florida with little to do, I'm going to continue to educate myself regarding the workings of my car.

[padgett]

Riviera and Reatta shared dashes. The FSM (all E bodies) shows one location (8A-201-6C in 88) for the BCM.

[Guest SwiftBuicks]

As stated I'm looking for the ECM.

[reattadudes]

the PCM (what you call the ECM) will be exactly where I mentioned, whether you have a Reatta or Riviera.

as I also mentioned, it isn't easy to see the PCM, it is right next to the A/C controller, and both are in black plastic sleeves, in a vertical (NOT horizontal) position, to the right of the glove box cavity.

it is quite difficult to remove the PCM for several reasons.

-first, the screws that secure it on the top are at odd angles, and it can be difficult to reach them.

-being that the sleeve that secures the PCM is also attached to the A/C controller, it is many times easier to remove both units at the same time. be sure to pop off the arm on top of the A/C controller before removal is attempted.

-as I mentioned, the hush panel must be removed under the right side of the dash to remove the PCM. many times, the removal of the unit will be easier if the carpeting is pulled back. clearances here are extremely tight.

-the plugs on the bottom of the PCM can be especially difficult to remove. be very careful that the plugs or wires are not damaged in the removal. also, be careful to not damage or pinch the vacuum lines for the air conditioning control unit. the units cannot be removed without unplugging them first.

Mike

buickreattaparts.com

[padgett]

Just a little expansion. I have never been able to remove an ECM (PCM in 91) without pulling the rug back. I do not remove the HVAC programmer.

If the clip and screw securing the vaccuum lines under the glovebox is removed, the lines can be moved behind the Control Module as it slips down. After replacing make sure the vaccuum feed line did not pop out of the horizontal connection (is only horizontal one).

I generally remove the torx screw holding the plastic bracket to the brace and just leave the bracket on the CM when removing, much easier than removing the nut.

There is a black rubber stud on the back (firewall) side of the CM. That makes removal/re-insertion difficult, I usually remove the stud (snaps out) before reinstalling. Like the third nut on the ICM, I feel it is more trouble than it is worth.

CM will run happily just lying on the rug after connecting the plugs. I usually verify reprogramming that way first.

[Guest SwiftBuicks]

>>Check and make sure the cover cap is installed properly on the ALDL (diagnostics) port located below the driver's side knee bolster.<< Found it. The cover is on securely. Ch 6, Section 1. under the heading <span style="font-weight: bold">General information</span> >>The Electronic Control Module (ECM) is often referred to as the Powertrain Control Module (PCM) on 1991 and later vehicles and is the same component. For clarification purposes this manual will use the terminology Electronic Control Module (ECM) when referrring to this component.<< <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: reattadudes</div><div class="ubbcode-body">the PCM (what you call the ECM)

</div></div> Since I see ECM on my CRT and never see PCM, I use ECM. I also located mine. I checked all connections there and around the brake switch. Nothing has changed. The Resume light is always on. The Cruise Control doesn't work. The error message still comes up, B334. The Electrical Problem light on the IPC still intermittently shines. The tach doesn't work. I see a NO ECM DATA message appearing on the display screen when extracting codes. According to Note 2 in Hanes >> <span style="font-style: italic">it signifies that the BCM lost communication with that particular system and cannot retrieve any codes until the communication line or circuit is fixed.</span><< <span style="font-weight: bold"><span style="text-decoration: underline">The car runs great.</span></span>

[Guest SwiftBuicks]

First of all, the quote in the last post came from Hanes. Second, I seem to have corrected the malfunction that was shutting down the cruise control and tach , putting up the error message and logging code B334 . There was no need for professional help. However, I bought a used FSM over E-bay which was helpful. To start off, I located the VSS, found it was not securely inserted and made sure I had a solid connection to it in place. Then, I took the ECM out, cleaned all the terminal contacts with a cleaner obtained at Rat Shack and re-inserted the Cal Pak and plugs. As Padgett states, I was able to place the ECM on the rug and render it operational. I did not have to remove the AC Controller, either. The CRT comes back now with a NO MALFUNCTIONS message on the check after ignition. I took the car out for a 12 mile test drive, running the cruise control and watching the tach. It all worked well. (The Resume light in the IPC still shines constantly, but I had already determined that was a separate problem, a short in the wiring.) I will keep the ECM on the rug for a while and see if things continue to run well. I was able to remove it without rolling back the rug by the way, but it was tightly fit and tricky to negotiate. I'll use Padgett's posted information when I replace it in the car. I am concerned that perhaps straightening out the wire harnesses when the ECM was connected on the rug corrected the difficulty and perhaps it will return once I put it back in it's place. Bending the wires might create a poor terminal contact.

[Guest SwiftBuicks]

Damn. I still have to spend time on this electrical problem. I've determined that there is a loose wire between the two Computer Modules that's breaking the connection after taking the car for a hundred mile drive. I also have no idea how to find where the power is coming from that lights the Resume msg. constantly. Oh, well, that's what's to be expected with a twenty year old car.

[Guest Drake]

SwiftBuicks, the only time the RESUME light activates, is after the cruise control has been activated, and you hit the brakes. Push the RESUME switch on the turnsignal stalk, and it should light up CRUISE on the IPC, and re-engage the cruise control to the speed you set.

I would try spraying contact cleaner into the turnsignal stalk, and then blow out with canned air.

I had a problem when I pushed the set button on the turnsignal stalk, the cruise control would activate after several tries. I sprayed contact cleaner (with the long thin plastic nossle tube) in and around the button & slider switch, and works like new.

(Hold an old towel under the turnsignal stalk, as the contact cleaner might drip on the seat & carpet).

[Guest SwiftBuicks]

I am working on a Riv and the Resume/Accel button is on the steering wheel not connected to the turn signal. As I have posted somewhere, the Resume light goes on with the mileage as soon as either of the thumb switches in the door handles is pressed. It stays on as long as the vehicle is powered.

[Guest Drake]

If I'd paid attention to you first post, I would'nt have waisted your time. Sorry bout that.

[padgett]

Resume light is clearly from a short in the wiring and may be related to the other issue. I had to replace all of the wiring in the '90s trunk because of an overheated harness.

Since it is on at all times the place to start is by pulling fuses and relays until it goes out. Once that happens you can review the harness routing until you find commonality.

Things like this can be a royal pain to find. My wiring issue began with door locks that did not work and appeared to result from a slipstreamed change in the trunk light from a standard single button lamp to a dual button without any mention. Even the owner's manual listed the wrong bulb.

[Guest SwiftBuicks]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: padgett</div><div class="ubbcode-body">Resume light is clearly from a short in the wiring and may be related to the other issue. I had to replace all of the wiring in the '90s trunk because of an overheated harness.

Since it is on at all times the place to start is by pulling fuses and relays until it goes out. Once that happens you can review the harness routing until you find commonality.

</div></div> Thanks, Padgett, I would never have thought of that. I will report back when I eventually make some progress. Part of the delay in doing these kinds of jobs would be the distraction the computer has vis-a-vis studying hard copy print (the FSM). The recently acquired FSM sits center stage on my other desk in the study, but I would much rather sit down at this desk in the office and waste my time. Luckily, though, I left the old laptop in Florida and that doesn't compete with the FSM on that desk. <span style="font-weight: bold">Drake</span> thanks for the apology.

[Guest SwiftBuicks]

O.K., as an update I replaced the ECM. This corrected the annoying failures in data line communication between it and the BCM. Now, the cruise control works along with the tach with no interruptions. I can also access the ECM codes from the CRT at all times. However, the resume light problem hasn't been resolved. I'm working on it, though. One other thing. You may find this interesting. When I bought the ECM from Auto Zone, the salesman, an elderly guy, and I saw that it wasn't an exact match with my OEM one. He said that I could plug the new one in and see if it worked before I turned in the core. In that case, he said, I could return it if it didn't work and get a full refund i.e. core charge and price of the ECM. Well, it worked so I brought the OEM one back in the new one's box. The wanted it that way to make the return easy. The old guy was busy, so a new employee, a black woman, helped me. She asked me if I had a return. I told her that it was a core return. I also told the old timer that the part they sold me had worked. She gave me a receipt and told me to go to the cashier. At that point the reigning manager and a customer started a discussion about automobile electronics with me. They wanted to do the talking and I let them. Then the old fella finished with his customer and reviewed the work the new employee had done. He found fault with it. (I suspected that his criticisms had more to do with his attitude to her than the facts of the matter.) The discussion regarding modern electronics continued while he fiddled and diddled with the paper work. He made some kind of explanation regarding what had been wrong. At that point I started to suspect that no one was listening to me except the black lady. All of a sudden he announces that I would be getting 200 and some odd dollars back. I thought wow, isn't that a surprise, the core charge was only $95. I kept my mouth shut as everyone else was talking and thinking that I was the guy who needed to listen. I had told the truth which was enough for me. Once I got back in the car, I realized that I had gotten a free replacement for my ECM. While driving home in the fixed car, it all fell into logic. It seems that the senior citizen hadn't heard my statements that this was a core return, that their replacement had worked for me, and that I was happy with it in my car. The gal had done it right, but he looked at the new box, didn't check it's contents and decided she was wrong. Then he registered it as a simple return, refunding me all my money. Wouldn't you think that he'll be retired soon?

[Ronnie]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I kept my mouth shut as everyone else was talking and thinking that I was the guy who needed to listen. I had told the truth which was enough for me.</div></div>It may have been enough for you but it would not have been enough for me. I try to live by the Golden Rule. It is, "Do unto others as you would have them do unto you.", in case you have never heard of it.

I may be the minority here but I take no pleasure in hearing stories where one person seems to be boasting about being able to take advantage of someone else by simply keeping his mouth shut.

Seems to me you took advantage of a man who was already bending the rules in your favor by allowing you to return an electrical part after you had plugged it in. Most auto parts stores have rules against that.

If you are looking for someone here to pat you on the back for being slick enough to get a new ECM for free, it won't be me. Some of us "old fellas" take pride in sleeping well at night knowing we did the right thing.

[harry yarnell]

I'm with Ronnie on this one. Someboy's going to buy your defective ECM that they put back on the shelf, and wonder why it doesn't work. Then blame the parts house.

I've been victim to this kind of scam. Bought a pair of shocks from a parts place only to find USED shocks in a carefully resealed box.Try explaining that to the parts guy when you try to take them back!

[matthewlawe]

Your overwhelming arrogance because you stole

from someone is quite disheartening. Shame.

The Golden Rule has served me well for the past

67 years and in applying this Rule, honesty and

integrity come to mind….

matthewlawe

[doitnow]

OK, fellows, I think the High Horse has been ridden enough.

[Ronnie]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SwiftBuicks</div><div class="ubbcode-body">I should not have come here and started this thread in the first place.</div></div>I agree with that 100%.

[matthewlawe]

Careful, your slip is showing....

matthewlawe

89 White/blue

[padgett]

Sorry but only Swift was there amd sounds like he tried. My rule is that at a maximum if I say the same thing three times and get ignored then my responsibility has ended and what will happen will happen. (something about leading a horse but my cross-synapse linkages always substitute "horticulture").