Failing ECMs

My 91 b2600i broke down two days ago. $286 in towing and mechanic fees later the truck was diagnosed as "bad ECM - no injector pulse."

After much searching I found a used replacement with a part number that matches the one that came out of my truck (UE46 67 650 A), so I ordered it and hope to be burning rubber again by Tuesday.

I thought ECM failures were very rare, however a couple sites I read in the last two days have indicated that the ECMs from these trucks have some design defects and they ALL fail eventually. Is that true?

I have an opportunity to buy a second used ECM for $40 and I'm thinking maybe I should get it as a spare to keep in the truck, mainly as insurance against spending hundreds of dollars on BS when/if this replacement fails too. What do you guys think?

If you can get a good one for $40, I say get it!

I'm an idiot. I've been looking at the ABS controller this whole time. The stupid mechanic who diagnosed my truck told me the ECM was under the seat, but that's the ABS controller. ECM is in the passenger side kick panel.

Now that I ripped my ABS controller apart looking for a burned out component that I could replace, I've got two controllers to deal with. joy!

Looks like I'm paying $200+ for a new ECM if I don't find one at the junkyard tomorrow.

I was just told the ABS controller isn't necessary because the truck will still brake normally, just without ABS (which I'm not sure was even working before anyway 'cause I've locked up the tires and they make a solid screech, not the choppy pulsing screech when the ABS activates). I've already got a new ABS controller in the mail tho.

No way in hell I'm paying $200 for an ECM to keep as a spare but I'm kind of nervous after reading about how common defects are with these. What do you guys do about this for your trucks? Just wait 'til it dies and suck up the $200 towing bill or is there a better way?

I know I can spend extra for a lifetime warranty but if it did fail I'd still be screwed on towing. I almost wish I had a carbureted engine.

I posted this on your other thread but I'll stick it here too just for good measure.

Good ECM repair info.


This is also a good site for you to get some good info on.



Also our trucks came with ABS only in the rear. it was to prevent the rear end from pitching out during a 4 wheel lock up situation, to help it track straight and not spin out and flip.

"4 wheel ABS... No, lets just put it in the rear." - Mazda

I was emailing with the guy at b2600i.com a bit but somehow I had missed your other link. I found repair instructions on some other sites but that thread looks like it might be a better resource. I was at the junkyard for most of the day today and got a ton of stuff including another ECU that appears to have the same cap problem. As soon as the replacement caps I ordered get here I'll try to fix them both and report back. I'm determined to get this truck running again asap.

thanks man!

I spent a good amount of time working on my ECM. I cleaned it as thoroughly as possible and replaced the leaking capacitor. I took a ton of pictures all thru the process and planned to post them here so others could see how I did it but unfortunately I wasn't able to actually get it working.

There are just too many tiny surface mount parts and the copper traces are too thin. I'm not set up for such fine work; it would probably take a low power microscope and fine tipped tools to get all the corrosion off the board and then be able to see which traces were damaged enough to need bypassing, and then actually install bypass wires plus reflowing solder on any components that looked questionable.

So simply cleaning the board and replacing the bad capacitor might work if you catch the ECM just after the capacitor starts leaking, but by the time things get bad enough for there to be noticeable symptoms the damage will be at a point where microscopic examination is required to identify and repair open circuits.

I ended up mailing the two ECMs I had to the guys at " target="_blank. One came back yesterday but when I put it in the truck it seemed to be worse than before (wouldn't even idle). I don't know which of the two ECMs was returned for sure but it looks like it's the one I got at the junkyard. The company is going to repair the other ECM and mail it to me for testing.

I'm hoping the other ECM works and the repair tech just missed something on the first one. In the meantime I've been trying to rule out other possible causes. For the symptom of starting and then immediately dying my shop manual says to check the wiring harness connections at the distributor, alternator and ignition coil. It also says to look for vacuum leaks at the intake manifold and verify fuel system pressure. Interestingly, the ECM isn't mentioned.

I tested the wiring from the distributor to the ECM, along with the other two wires leaving the distributor but it was all fine. I didn't test the alternator or ignition coil connections but I did unhook them and they looked fine other than being pretty dirty where there weren't seals. I have since found those connections on my wiring diagrams and will probably test them later, tho I'm wondering if that would be a waste of time.

My mechanic pressure tested the fuel system right after I broke down and it was fine so I'm assuming that's still the case. I may look for vacuum leaks when I have time though. Is there an easy way to do that other than just finding a diagram and checking all the hoses one at a time?

Since I pulled apart my ABS controller and then "repaired" it and put it back in the truck I'm wondering if there's some way to know if it's working. My shop manual says absolutely nothing about ABS. That controller had nice big components and thick traces on the board like I'm used to so I'm fairly confident that it's fine but want to make sure that isn't playing a role in the truck not starting right now and if possible a way to test that it's working properly. Anyone know a procedure for that?

Thanks for your help guys and let me know if you want to see pics of my ECM; I could post a few if anyone really wants to see what it looks like but since I wasn't able to fully repair it I doubt posting my procedure would do anyone any good.