what would cause my Engine Control Module to do this ?

http://i1334.photobucket.com/albums/...psc4fe9d33.jpg

 

It looks like that big green capacitor puked its guts out. In other words, twas age that killed the beast...

 

Doesn't look like the cap to me. Something next to it got really hot and turned parts and board into charcoal. I would say it's in the power supply regulator section. Unfortunately, when those things go it's usually not pretty, because of the power involved. I doubt there's much hope of salvaging it, unless you had the schematics and could build a small breadboard to replace the burned section.

As far what causes this, who knows. Occasionally a part just fails due to a latent defect that finally rears its head after 25 years. A transistor base-collector junction breaks down, draws lots of current, gets hot, draws even more current, burns the parts next to it, burns the board, finally blows a fuse or opens up a PC board trace, and it's all over but the cleanup. Generally only takes a few seconds.

My guess is it's nothing you did, specifically, other than use the truck.

 

Electrical engineers!!!

Although I must admit that my ECU has taken a beating as I was trying to figure out a bunch of electrical issues... still operates as it should!

 

Generally electronic modules like the ECU are pretty well protected from outside abuse. Toyota (and other auto manufacturers) have to do that, or they'd be replacing ECU's all the time. The manufacturers actually have some pretty severe torture tests for the electronics during the design process, because of the harshness of the automotive environment.

That's why I suggested it's not likely anything the OP did, rather just a latent defect that is impossible to catch at the time of manufacture. Those are rare, but they exist.

 

Agree with Ron.

However, maybe there are things we can do to help extend the life. I..e, minimize unnecessary power-up/power down cycles of these components. One thing I have in mind is the power windows/rear wiper controls. Currently, each time someone wants his window rolled up or down (Only the windows and nothing else), he'd have to turn IGN on, which subjects the ECU to one more power-up/power down cycle.

I want to move my rear window control from IGN circuit to Accessory. Why not all the way directly to battery? So if any of the switches short, or relay module messes up, my rear window will not roll down while truck is unattended.

 

RADRunner, funny you mention that.

I dislike having to have the key in at all to operate the radio, windows and cig. lighter/12 volt outlet.

I understand there are reasons for it... but I'm defi. going to hack those sooner or later.
I added a 12-volt socket to my A4 so I don't have to leave the key in for charging the phone.

Thread jack a little. sorry!

 

How much current do the windows take? I suspect, compared to the radio, a lot. You could leave the radio on for about a year before you ran the battery down, but I'm sure the battery would run down much faster with the windows going up and down. Throw in an older battery, and a very cold day, and you could have trouble.

I suspect that is part of the reason the windows are on the IGN circuit (where the engine is usually running) instead of ACC. This doesn't rule out your idea, but it's something to keep in mind.

 

ECU failure is rare IMHO, I'd just get one on Ebay and be done with it. You can get them for around 100 bucks or jank it from the junk yard. Just match the part number and you'll be good. As far as power up cycles, who knows if that has a legitimate affect on the ECU, I'd just run a used one and have a spare if it really bothers you. Although the 12v outlet directly wired is a good idea.

 

The finals at the top control the injectors.


Most of that section is the device control for the VSV's, I cant see all the etching markers that are to the left of the green thing and I don't know where my extra ECU is to open up and look.
I would say that a B+ source got shorted to one of the inputs from wire wear or AFM, TPS, VSV, Distributor or igniter going bad and shorting internally.
Bad wire splice could cause.


There fairly resilient otherwise.