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ECU Replacement Precautions?

Thu Dec 17, 2009 4:23 pm

If you swap out your ECU for another one that's the same, are there any special precautions that must be observed?

Just to be safe, I'm going to unhook the battery, but are there any other concerns, ie static electricity charges, etc?
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Fri Dec 18, 2009 3:05 am

The automotive electrical environment is pretty bad from an electronics perspective, so the ECU is made pretty robust. Not much to worry about if you are just swapping it for another one.

Fri Dec 18, 2009 3:37 am

You have nothing t worry about Rick. Swap it in and go.

Pull your efi fuse, swap ecu, replace efi fuse (1min wait assumed) fire it up.

Fri Dec 18, 2009 1:56 pm

To be safe than sorry, I prefer to disconnect the battery than just removing the EFI fuse.
You'll never know what changes has been done with time that can feed power from unexpected source.

What ever you do, wait at least 30 seconds from the disconnection time before you start working.
This will give the time to all the capacitors to discharge.

Fri Dec 18, 2009 3:55 pm

I would disconnect the battery for sure and ground myself if I'm worried about electrical discharge.

Fri Dec 18, 2009 8:12 pm

LOL
gimmie a break guys.

take the key out. change the ecu. put the key in . start and go.

Fri Dec 18, 2009 9:09 pm

klue wrote:LOL
gimmie a break guys.

take the key out. change the ecu. put the key in . start and go.

My cousin went to replace his burnt out 4age ecu in his MR2 and didn't disconnect the battery. Yep... It happened again...

Secondly I'm sure you won't get a nasty eletrical burn from the wire harness but after seeing my friend's dad's nasty lash from an eletrical burn I will always disconnect the battery and usually put a towel on top of it (he didn't even get it from the battery). It looked like a brown recluse spider bite...

Re: ECU Replacement Precautions?

Mon May 16, 2016 2:48 am

Requesting some advice here, before I lose a few knuckles.
I have half of my dash ripped apart right now to replace my ecu. Dropped my glovebox, too..
Am I correct in assuming that the wire connectors are to be removed from the passenger side? My vehicle is a 1990 ST185 with left hand drive. I can barely see the connectors..

Re: ECU Replacement Precautions?

Mon May 16, 2016 6:10 am

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sarnodude wrote:I have half of my dash ripped apart right now to replace my ecu. Dropped my glovebox, too..
Am I correct in assuming that the wire connectors are to be removed from the passenger side?


Cant remember whether I had to disassemble the dash or not but I believe the ECU can be removed without disassembling much. And yes, you are correct about the connectors being on the right side. Here's a pic I took years ago for some reason, I remember it being easy to remove but the shifter/radio center console may have been removed. . .

IMG_20130627_085214_362.jpg

Re: ECU Replacement Precautions?

Mon May 16, 2016 12:43 pm

If you've removed the glove box then you should be able to access it from the passenger side relatively easily. The ECU is connected to a bracket that is connected to the car. You can remove it either way. It's been nearly a decade since I've gotten in my Alltrac but it is definitely easier to dive head first into the center console from the passenger side to access the ECU. I didn't need to remove the radio or bezel.

Re: ECU Replacement Precautions?

Mon May 16, 2016 9:14 pm

Tkanks for the posts, I am going to dive in tonight, and give it another shot.

Re: ECU Replacement Precautions?

Tue May 17, 2016 9:53 am

There's no need to pull anything apart to get the ECU out.
Pull the rug back on the passenger side, disconnect the 5 connectors [3 on the ECU and the 2 beside it], remove the 10mm nut for the bracket.
Go to the drivers side, pull back the carpet and remove the 2 10mm nuts for the 2 brackets on that side.
There are also 2 brackets for the wiring that are attached to the ECU. 1 is for the COR [Circuit Opening Relay; for your fuel pump] and one for the 2 wiring harness connectors on the passenger side.

Once all 3 nuts are removed the ECU is still a bit of a PITA to get out because the brackets are tight against the 3 studs.

I've found it easier on occasion to remove 1 or more of the brackets from the ECU. Each is held on by 2 phillips #2 screws. Be careful you don't strip out the phillips heads; it helps if your hands/wrists aren't weak. :P

Re: ECU Replacement Precautions?

Wed May 18, 2016 4:21 am

Hey FC Zac, what the Hell happened the your ECU? Looks like an elephant stepped on it! LOL

Re: ECU Replacement Precautions?

Wed May 18, 2016 4:34 am

Rick89GTS wrote:Hey FC Zac, what the Hell happened the your ECU? Looks like an elephant stepped on it! LOL


That's a great question I would love to ask whichever previous owner had the car before me! It looked like they used it as a hockey puck! Even though the ECU was in rough shape that picture looked worse than it actually is because of the plastic/vinyl cover thingy that sticks to the top. I had to change this one out years ago due to a bad diagnostics board, here's what the inside looked like.

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