Replacing the PCM/ECU? - Mazda Forum - Mazda Enthusiast Forums

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Old 10-29-2010, 08:30 PM
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Default Replacing the PCM/ECU?

Hi all, first time poster in need of some input.

I own a 2005 Mazda 3, 2.3L Automatic, purchased used about 4 months ago. It's currently in the shop, and after three days of diagnosis the mechanic wants to replace the computer for a total of $600 (~$300 for the computer itself).

Here's the background info on the problem I'm having with the car. The car has run great since I got it. The Check Engine Light has been on since two weeks after the purchase; the diagnostic test revealed only a O2 sensor, and the mechanic recommended that I don't worry about it. So the light has remained on, and I have not had the O2 sensor replaced. The car ran great up until last weekend. I drove to my destination without any problems. When I got in the car to return home, the AT light came on and the car would only rev to ~2,000RPM. (It did not red-line at 2000, it simply stopped stayed steady at 2000). I checked the transmission fluid, there was only about 1/4 inch on the bottom of the stick, so I added some. Didn't solve the problem, but I drove it home since I was pretty close. It would only go about 20-30mph, shifting when it picked up enough speed. One of my friends recommended I reset the computer, so I did. The AT light did not come back on, however the problem persisted. I'm fairly optimistic it's not a mechanical problem with the transmission. I have never experienced any problems shifting or accelerating, and again, it seemed to run perfectly fine until this problem suddenly occurred.

I took it to the mechanic on Monday. He said he got a code from the computer for the Mass Airflow Sensor. They replaced it but it didn't solve the problem, so they removed it. At that time, the mechanic told me that he was concerned about the computer, since it appeared to be a "salvage" computer and appeared to have water damage. The carfax for the car is clean, fwiw, however the previous owner did make a few minor modifications, though I don't know why he would have replaced the computer.

At that point, with no other codes being registered by the computer, they started a 3 day diagnostic process testing the sensors and the wiring and connections. Throughout the process at various times, the computer registered several codes for various things from the transmission to engine problems, though the codes came and went. Also, the computer didn't register information or codes that it should have throughout the process.

For this reason, the mechanic said he was "as certain as [he] could be" that the computer needs replacing, for the price quoted above. I don't disagree with him, however I fear that the computer is not what is causing the problem above, but simply a means of correctly displaying the cause of the problem above. So that adds up to $600 for the computer, + $xxx for the real problem. I can afford one or the other, but not both.

So to save money, I want to know if it's reasonable for me to be able to purchase and replace the computer myself. I have a few questions about it, though.

-I only have the model number of the computer CURRENTLY in the car, which apparently is not the ORIGINAL computer. Can I purchase ANY 2005 Mazda 3 2.3L Automatic computer?

-Will the computer require programming before it will work? Or is it essentially plug-and-play?

-What is involved in properly replacing the computer? Is it correct that it is beneath the battery?

FWIW, I'm currently looking at this computer:

Thanks a lot for reading. I posted the full situation incase someone has some input on not only replacing the computer, but any other possible causes of the problem. Thanks in advance for any information.

Last edited by mach42006; 10-29-2010 at 08:35 PM. Reason: Additional info.
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Old 10-30-2010, 02:39 PM
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Ill start by answering your questions

-If you do you have to make sure that the options match what you have, like abs traction control

-Yes it will require reprogramming, parameter reset, immobilizer reset among other things

-Yes it is under the battery, just a few bolts that hold everything down and pull the wires to the ecu

Given the problems i can see why he would say that, he may be on the right track, seeing how as the transmission and engine controls are in the same ecu, but ive got a few questions. Carfax says that the car is clean but it only knows what its told, previous owner could of had work done under the table, what are road conditions in your area, does the ecu model # match the vin (only a dealer would know). A number of things can cause the problem (i dont know what tests hes really done) it can be from a loose or corroded terminal(s), with the absurd amount of engine movement for the sake of no cabin vibrations and seeing how its an 05 there might be broken wire(s) anywhere along the harness (hopefully hes rules most of this out during his tests) working at a dealership, replacing the ecu is a last resort, and during my training its been known to not fix the problem. I hope for your sake you took it to the right guy but a diag resulting in needing a new ecu is not out of the question
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Old 05-05-2012, 12:28 PM
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So...My car is 2003 Mazda 6 3.0L V6 S (AT).I have problem with ECU,ECU number is "ECU PCM Brain Computer Engine BDD3 AJ58 18881 G 3.0L V6 S ECM".The thing is that Ecu's one of the cheap/micro scheme burned,and because of this one of the cylindrs stopped working(but car is still running).My question is next:Is there any difference and if it is what difference is between 2.3L ECU's cheap and V6 3.0L cheap???Can I use 2.3L ecu cheap for V6 3.0L???
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Old 05-06-2012, 01:00 PM
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Location: Manor, TX (Outside of Austin)
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I really wouldn't think so. PCM's are usually very specific to a certain vehicle with a certain engine. With the Mazda PCM's being "untunable" I don't know that anyone could crack the code to install information relevant to your vehicle?
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Old 05-06-2012, 02:17 PM
Join Date: Dec 2011
Location: Canada
Posts: 2,637

The only thing I can add is that Hypertech can add a power program (update) to the ECU of the 4 cylinder, but they can't do it to the 6 cylinder. The 4 cylinder may be reprogrammable, the 6 cylinder is not (requires a piggy back tuner).
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Old 05-15-2012, 06:28 PM
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Posts: 235

Lol this is ironic to my post. JET can tune our mazda3's/6's ECU's. If you buy one off of ebay like I did, make sure every visible number matches. the PCM's are NOT compatible even 1 letter or number off will render your car inoperable. Once you get it, The dealer will need to flash your VIN number into the PCM as well as probably flash program it. You will need to bring all your keys with you as they will have to flash your keys codes in the the PCM as well. My Dealer charged me $65 for the keys and $125 programming the VIN so $190 total. you can by an Ebay PCM for what $200? $390 total Vs. $600

Your dealership might be able to look up your VIN number and tell you exactly which computer to get. IDK why or how someone put a v6 mazda6 computer into a 2.3L mazda3.
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Old 02-06-2016, 03:59 AM
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Location: Sydney
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Wink Update?

Hi there,
I know this is an old thread, but just wondering what happened in the end? Did you get the PCM replaced?

I'm having a similar issue with my Mazda 2, don't want to fork out $3000 unnecessarily, but not sure what my options are...
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