The ECM is dead on my 2003 Toyota Corolla. What are the risks of installing a used ECM?

Will the ECM need to be reconfigured?

I've heard it might have issues passing DEQ?


3 Answers 3


The biggest risk in my mind is getting one that does not work. I'd be nervous about grabbing one from a boneyard, even if they'll replace a dud, going through the work of installing it to find out you've got a bad one would suck. Getting one from a vendor selling refurbished units with a warranty would be an entirely different deal.

As far as to whether it needs to be reconfigured, possibly not, as long as it comes out of a donor Corolla of the same year with the same powertrain. Depending on where you get it from, you may or may not know what it has in the way of loaded firmware, but that might not be a problem. It's possible there was fix issued that requires a hardware change, but I think that's pretty rare.

I suppose there could be issues with emissions if they're checking a VIN stored in the module against the one on your registration. Or if you're in California and you don't get a module with some California specific firmware load.

Having a dealer swap in a new one will eliminate any uncertainties regarding firmware and emissions. You should get the latest firmware and they'll use your VIN if it's actually stored. That will be the most expensive route, though. It's possible there are aftermarket sources that have the capability to bench flash a module before shipping it to you that would take care of all that, but I don't know of any of the top of my head. It looks like Toyota has made the tools available to flash the ECM, so, actually, a properly equipped shop can do this, too. Sounds like there might be some kind of extended warranty on the ECM from the quick bit of forum surfing that I did. Check into that before you go out of pocket on a replacement.

You probably ought to try and figure out what killed you existing module. If it was killed by some kind of electrical problem, the replacement could suffer the same fate.

Oh, and in a 2003, I'd think it would be more of a PCM than an ECM. The difference can be a little fuzzy, but in my mind, if it's controlling the transmission shift points, or would be if the vehicle had an automatic transmission, it's a PCM. Hmm, looks like Toyota calls it an ECM though.


I actually replaced an ECM myself on my '99 Avalon - twice actually. The first time I bought a ECM from a junkyard for about $40 without shipping. I plugged it in and unfortunately it was DOA. Shipped it back and ordered another ECM from a different wrecker. this time it worked fine (thankfully) - although as a relative of mine is an Electrical Engineer I actually had some extra industrial grade tools to diagnose my car.

But going back to the ECM chip, for me I simply had to plug it into the correct slot. Even though I bought a used chip though, I highly suggest you buy new because with such a critical engine component you really don't want to chance it.

If you really wanted to be cost effective, you can even have a trusted mechanic order the part and install it - I don't think this is a job only a dealer can do, and if the mechanic can't directly order the part (which I doubt) then just go to the dealer, have them order, and then bring it to the mechanic. The markups dealers do on even modest repairs is seriously absurd which is why I always try to go to a trusted mechanic when possible.


I work in this field. I'm an embedded engineer who writes code for instrument clusters and ECUs.

ECM (or ECU) often have stickers on the back of them denoting both a hardware revision level and software revision level. I would make sure both those values match the old module you are replacing or that you have some sort of confirmation that the one you are purchasing is backward compatible.

ECU/ECM are essentially single board computers specialized to marshall data on & off a CAN or LIN network - some ECUs are apart of a MOST ring. Depending on what networks (CAN, LIN, MOST, etc...) the hardware & software of the module really determine how compatible the unit will be in your vehicle with other ECUs on the bus.

  • @Mark: not sure of the field update procedures per say. I use to work on Ford SYNC (now on Cadillac CUE). The stuff I deal with is usually a step above an "ECU" where I typically am working on a full blown embedded module. The more sophisticated the higher the frequency of updates. In short, most (if not all) modules have a way to query them to get their software rev & hardware rev levels.
    – Kilo
    Commented Oct 17, 2012 at 3:08
  • I ran into the very issues you raise here, see my story here: mechanics.stackexchange.com/questions/41811/… Commented Jul 19, 2019 at 23:06

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