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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 😉 – plainclothes Apr 30 '17 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 '17 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 – ElectronicsNewbie May 2 '17 at 18:55
  • I apologise, I misinterpreted your post. Thank you for clarifying. – Inlandsmog May 5 '17 at 21:02
  • @Inlandsmog You do have a point though! I checked the was a direct connection from the fuel pump relay to the ground that was responsible for the flooding. Once fixed it went away. Thanks for the lead. But the old ECU is gone for good. Communication via the K-line was restored and there was battery power, yet the ECU failed to communicate. Also a J2534 device was required to change certain ECU parameters in the course of the ECU replacement, see mechanics.stackexchange.com/questions/44157/… – ElectronicsNewbie May 6 '17 at 4:59
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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. – ElectronicsNewbie May 5 '17 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 '17 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 '17 at 15:33
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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 – ElectronicsNewbie May 5 '17 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 '17 at 13:24

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