I own a Mazda MPV 2000 with a faulty ECU.

The vehicle has an immobilizer.

It will not start with the former ECU.

It floods the engine with fuel.

After extensive diagnostics on the vehicle and the ECU it was determined that I have a faulty ECU.

How do I mate the new to me ECU to the keys and the immobilizer in the vehicle?

Is this something that an enthusiast can do?

What tools do I need?

I know I need to get a code word based on the immobilizer, the actual programming itself, it is something a DIY can do?

Additional Detail:

The code word is based on the serial number of the immobilizer

The mating of the new ECU to the old ECU and immobilizer can be done without contacting the dealer, it even seems it can be done manually without any computer equipment, will confirm that in the next 48 hours

Remotely related issue: How to program a transponder key of a 2000 Toyota Sienna

Additional detail:

ECU recognizes keys but does not start the vehicle, if all fails, will purchase a new immobilizer and mate it to the ECU so it can start

Additional detail:

I don't know what magic the locksmith wants to pull tomorrow but should it fail, I got two choices: get another immobilizer (brand new so it can be programmed to communicate with the new to me ECU or get another used ECU which has the exact same part number as the one which is bad, I lean towards the former not the later!)

Additional detail:

It appears that Mazda made internal changes to the MPV PCM and immobilizer in later models which necessitated a wiring change after PCM/immobilizer replacement. This means that just before I go through the expense of replacing the immobilizer, I am going to switch the ground which happened to be immobilizer harness terminal B in my built in 1999 as 2000 model to immobilizer harness terminal C which appears to have been the standard from 2000 going forward, see diagram attached, as you can see, there is no B in the circuit diagram. In my vehicle, the ground is connected to B instead of C. Having upgraded the ECU to the latest version number in which this change was effected, I also need to change the ground wiring at the immobilizer wiring harness to ensure that the immobilizer is connected to the vehicle's grounds!

The immobilizer recognizes the keys but cannot start the vehicle, the locksmith cannot explain the situation, but this looks to me like a case of an incomplete ground between the immo, the PCM and the vehicle. Late model changes to immobilizer circuit by Mazda

Full circuit diagram

  • Just switch to sidedraft carbs and dump the security system 😉 Apr 30, 2017 at 16:31
  • Your statement that the vehicle is flooding is not an immobilizer issue. The immobilizer function is to kill the injector pulses and/or interrupt the the starter operation. You may have another issue going on.
    – Inlandsmog
    May 2, 2017 at 18:45
  • @Inlandsmog In the course of repairing a no-start condition due to a faulty crankshaft position sensor, someting nasty happened to the battery connections and since then the car refused to start, all tests and diagnosis pointed to a fault within the ECU that flooded the engine instead of sprinkling fuel, the recommendation was to replace or repair the ECU, before this mistake it would start and go off almost immediately May 2, 2017 at 18:55
  • I apologise, I misinterpreted your post. Thank you for clarifying.
    – Inlandsmog
    May 5, 2017 at 21:02
  • 1
    Yes, there are a lot of sleezey handymen who call themselves locksmiths, but I am here to say we are not all that way. The cheapest Locksmith is not always the best choice but unfortunately most of the general public choose the cheapest! We program ECUs and keys back to the immobalizer and have been around 50 years. I also do this for the dealerships. Make sure your dealing with a good reputable company!
    – Keystogo
    Aug 10, 2017 at 23:45

3 Answers 3


None of the provided answers are specific about programming a replacement PCM to a 2000 Mazda MPV so I wanted to chime in for any future visitors needing help.

There are two things that need to be matched up when changing this PCM.

1. The engine calibrations (software that runs the engine) You can usually buy the same part number computer with same software code and be good here but if you can only find the same part # with a different software code then you can use a j2534 tool along with a subscription to mazda and then flash the correct calibrations. https://www.mazdaserviceinfo.com/pcm-reflashing

2. The immobilizer system (if equipped, not all mpv's have one) The MPV uses a separate immobilizer box that then verifies a unique ID code with the PCM that it stored inside when they where first matched together before it allows firing. This code is unique to each box so even when the part# & software is the same this unique immobilizer code will need to be corrected inside the pcm. It verifies like this. KEY > IMMOBILIZER > ECU . When all are good the immobilizer deactivates.

These old systems will not let you learn a used immobilizer box and ecu together or program when all keys are lost diagnostically. The easiest work around for this is to either buy a secondhand key,immobilizer & ecu as a kitted unit. Another common work around is to clone the synchronization data directly out of your original ecu's eeprom memory (labeled 77005 ) into your new ecu's eeprom memory.

If you unfortunately do not have the original ecu any longer then the immobilizer box needs to be removed and the eeprom read from the hc05 mcu so that the sync codes can be found and matched to the replacement ecu. Its best to remove the mcu for reading and its in a very tight spot so I'd say it requires very good soldering experience.

The only part that is fairly easy to DIY is the 77005 cloning. Its just a soic-8 eeprom chip of the ST 95xxx family. Beyond that I would recommend someone to send the parts to a specialists.

One last thing that could be tried (but is untested by me) disconnect and remove the immobilizer box. Then replace the pcm with one out of a mpv that has no immobilizer system installed (most do not so this should be easily found in junk yard). Have pcm flashed to match engine if needed.

Dealers will want to replace the ecu, key & immobilizer with virgin units. (or they secretly just call people like me in to do the job instead for them with end user never knowing) but you can get it done with used parts regardless of what they may claim.

On a side note for others. IF your MPV does NOT have an immobilizer, then you MUST find a replacement pcm from another MPV that was with out an immobilizer or you will run into some immobilizer problems of your own.

  • 1
    Buy the same part number computer with same software code and be good: Vehicle came with a GY04-18881-E. Other marking on the computer include ERY4, MLM-812, XU3F-12A650-PE which of these is the software code? The replacement computer was a GY04-1888-H other markings on the computer include ILC2, MLM-832 AND XU3F-12A650-AMC. I have two options get a key,immobilizer & ecu from the junkyard or get an ecu without antitheft. I have confirmation that the later option will work (but a modification need to be made to the fuel pump relay driver to take the immobilizer out of the equation Feb 28, 2020 at 17:20
  • mazda-parts.com/v-2000-mazda-mpv--dx--2-5l-v6-gas/… ..... The main number to conern yourself with is either the "tear tag" which is the 4 big digits or the GY04-18880-X number. Looks like G is the newest (except for california) replacing GY01-18-881C, GY01-18-881D, GY01-18-881E, GY01-18-881F. The "H" replacement you have is same thing just slightly updated for some minor improvement of engine controls. Flashing any one of the above numbers would give you the end resauly of GY04-1888-G unless your in Cali then it would be GY04-1888-H .
    – narkeleptk
    Feb 28, 2020 at 22:10
  • Mine is California which was why I got the one ending in H Feb 29, 2020 at 0:50

I went through the "replace a faulty engine computer" drill a year or so ago and it was quite an ugly experience.

1). The manufacturer did NOT sell replacement units. This car was 15 years old. If your manufacturer supports it, having this resolved at your local dealership is your best chance for success.

2). In my case the engine computer failed because of a IGBT chip failure within the box. The control CPU was fine. Memory and communications were fine. The unit just wouldn't generate a spark signal.

3). We ended up purchasing a replacement unit through Autozone. Although they initially made a few mistakes they worked hard to correct them. As a result of that repair I'm a strong Autozone fan for life.

4). We still had to get the unit reprogrammed by the dealer, because of the keys and integral anti-theft system.

5). It might be possible to purchase a used engine computer (junkyard?) but you will definitely have to get it reprogrammed. In some cases there are hardware differences e.g. Six cylinders or eight? My unit only had chips to control six cylinders.

6) Steer clear of locksmiths to reprogram the anti-theft stuff. Those guys were sleezy crooks. I did get all my money back after filing a claim thru my credit card company.

Here's the whole saga... note I get paid by the word. Ouch for some reason that link gets corrupted. http://www.allfordmustangs.com/forums/v6-tech/863298-2001-no-spark-no-start.html#/topics/863298?page=1

In short start at the dealer. If they say no find a high quality auto parts place. Good luck with it.

  • Your experience was nasty. Hope I don't have to pass through that.Actually I am in the middle of this. I have learnt that there is a chip that holds the immobilizer data in the PCM, one way of getting around this is to read the value off the old ECU and write it to the one in the replacement ECU. May 5, 2017 at 12:29
  • Couple of things here. When you buy from Autozone they program the unit for your make and model and odometer. The only piece left is to synchronize the anti theft system to your RFID keys. The dealer also has the ability to clone the entire unit from the old if CPU / memory is still intact.
    – zipzit
    May 5, 2017 at 15:26
  • In theory the fly by night locksmiths have the software tools to program your new unit for keys. No way will their tools clone the entire unit. But I found those guys to be sleazy no integrity dirt bags. Beware. Step #1 there is ask for drivers license. Take photo of license and locksmith for court purposes. When they refuse (and they will!) go to your dealer.
    – zipzit
    May 5, 2017 at 15:33
  • @Zipzit Your experience with one crappy locksmith is no reason to bash an entire trade. Many of us are very professional and far surpass what your dealer can do. In fact I get called in by many of the major dealers in my city for jobs they run into trouble on relating to module adaptions and immobilizer systems. Their methods are limited by their oem software. Where as I am not, I carry both oem and the top aftermarket tools for ALL makes and models. In your case a simple parameter reset was all you needed since your pcm had been pre-flashed. That's a $60-$90 charge with mobile included.
    – narkeleptk
    Oct 18, 2019 at 1:05
  • I wish it was just one guy. Call four totally different places and the same person answers the phone. First guy didn't know what he was doing, calls 2nd and 3rd guy. These sorry losers left quite an impression. If I call you, first thing I do is take your photo, and ask for government issued photo id. Then I check your license plate, sticker and vin tag. Hesitate or balk anywhere and I immediately call the police. These guys were beyond sleazy. Show me where the lock smith industry is trying to clean up corruption among its ranks, and then I'd be impressed. In the meantime, buyers beware.
    – zipzit
    Oct 18, 2019 at 5:10

Experience with other vehicles means you will need the computer / linkcable / software (not an aftermarket one but usually a dealer level) that matches your vehicle and that will be able to code your ecu to your car. Not a function usually possible with aftermarket readers that are used to extinguish the engine service light for example.

  • You are right that about the above. But I also learned that the possible to bypass the computer/linkcable/software if both units are exactly the same, same part number, and have not been internally changed, and by that is meant that the chip the contains the immobilizer code has not been changed from one version to another May 5, 2017 at 12:48
  • That will not work with my vehicle ... some people find they have to replace the keys, steering column, dash unit and ecu all together when taking / upgrading parts from one vehicle to another.
    – Solar Mike
    May 5, 2017 at 13:24

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