Can I run any tests on my ECU ?

Following on from my crank position sensor thread, where I did not seem to be getting any voltage from my ecu, I have now discovered that my

EOBD / OBDII can not establish a connection to my car. Assuming I remove the ecu, and I can rule out a loose connector, are there any methods for testing the ecu, to see if it is dead or not ? 

Any help would be most welcome.



What model car Phil.

I’m aware of an issue with the MK2’s where a terminal can corrode on the ECU.

There was a thread a few months back with images and a possible fix.


Might be related, or at least worth a look. ???

Thanks for the reply Keat.

My car is a 2002 Mk 2.5 1.8 VVT 107KW (NB18P2).

I have already run a search on the forum, but I’ll try again using your info.



Oops. I did not read far enough to see your link.  

I read through the post that you linked, very interesting by the way, then went out to the car thinking that my problems were nearly solved.

I removed and thoroughly inspected the ecu, its connectors and the connectors on the wiring harness.

My conclusion is as follows:

If these had just been unwrapped, having been purchased as new, I would not be disappointed.

On the board itself, all pins are present and correct. There is not a blemish or trace of corrosion on the board or the connectors.

So I am back to my original question. Is there any way to test an ecu, or do I have to bin it and go for a replacement ?

In the event that this info might give some clues:

The references on the box are S BP6JD, 971224P, BP6J, EGI BP6J 18 881D, 279700 - 1224.

The part number of the card itself looks like 279721 - 1201.

And, if I have to replace the ecu, what are my best options ?

As always, advice and suggestions are more than welcome.



You have to replace the ECU, the specific matching imobiliser that sits near the steering wheel and the get keys cut at Timpsons with the shape of your original key but the electronic code number from the keys that are matched to the replacement ECU which should be supplied by whoever sells you the combo.

There was a company that moified some MX5 ECU’s to alter the mixture they may be able to help.

But, presumably, those who have installed a more modern, programmable ecu, Megasquirt and ME221 / ME442 are those I have heard of, have solved the immobiliser issue. Any idea how ?

I’ll call the company you mentioned Tomorrow. 

Unfortunately, I have run out of time, as the wife and I are heading back to France on Monday, so my MX5 will be left to its own devices for a few months.




Hello Philocd

14 months ago Carl at CBS Autos Nelson BB9 7BJ fitted a 1.8   VVT engine into my 94 1.8 Eunos S Special, the o/e engine with 200k Kms still ran fine but the VVT engine had only 35k miles of use; the transplant just had to happen!!

The MK2.5 VVT ECU was replaced with a ME221 ECU simply to avoid the hassle of the immobiliser problems often encountered with the MK2.5 VVT system.

10k Kms on I must say the transplant has proved successful & trouble free.

Enjoy France.



The OE system has a transponder pill embedded in the head of the key and a reader coil attached to the ignition lock barrel.
When you key on the Immobiliser ECU activates the coil and reads the transponder code. If it recognises the code as valid, it then communicates with the Engine management System to allow the engine to fire up.
Any aftermarket ECU will allow you to delete the immobiliser function, but with possible insurance consequences.


Make your mind up and stop wasting peoples time.

One minute you are asking how to test and tweek the Mazda ECU and now you are wittering on about changing the ECU to an aftermarket ECU.

WTF are you trying to do?

Get an original ECU working or are you wanting to change the ECU for an aftermarket unit.

What I am trying to do is quite simple really. I am trying to get my car started and back on the road.

The title of this particular thread seemed clear  enough to me. I asked if there is any way to test an ecu.

Keat63 suggested a link to a thread about possible corrosion issues, to which I responded, eliminating this issue.

You suggested swapping the ecu, the immobiliser and getting new keys cut.  

You also suggested DCP Tuning, for an ecu modification. (The phone number is “not available”). 

I did not reply questioning the suggestion of replacing 17 year old components with other 17 year old components. I  simply asked if you knew how the after market ecu handled the immobiliser issue.

KeithW posted a recommendation to swap my original ecu for an ME221.       

Fred Gassit posted an explanation as to how the immobiliser system works, basically elaborating on your post.

I do not know how the word “wittering” is used in your part of the world, but, if one reference to after market ecus is considered as wittering and time wasting then I must be guilty as charged.

However, in my defence, would it be appropriate to point out that I have yet to receive an answer to the question posed in the title of this thread?  

In any event, my objective remains to get my car back on the road.

On Amazon and eBay, U.K., France, Spain and Italy, (Original registration was Italy), I have not found a compatible, second hand ecu, immobiliser and key set. There are a few sets available, but none are the BP6J which is installed in my car.

i have been quoted a minimum of £2000 for a new ecu. (Probably more than the value of the car).

Nobody seems to be able to tell me how to go about reviving my existing ecu.

If there is a better alternative, to the £600 ME221, I am more than ready to consider it.



in my opinion, the way to ‘test‘ an ECU is to check all of its inputs are correct and then check all its outputs are working. Easier said than done I know, but if you get hold of a Terminal Voltage list it can be done. If its getting all the correct inputs but isn’t outputting, then it can be considered that the ECU may be at fault. Have you checked the obvious like all fuses? Power supply can be considered as an input.


May I suggest you copy your original post and forward it to Skuzzle Motorsports…

“Skuzzle” is in the business of 5 performance & track modding and most importantly for you, ECU mods/flashing/ spares ( maybe).

There’s not a lot if anything he won’t know. I’ve never used him, BUT…Nick gave me honest advice recently not to buy a flashed ECU for my old NA from him as it would have been only worthwhile as part of a modding…so that was honest.

He does take time to reply though… 

01962 776 167

Thanks for the reply Robbie.

I did not imagine that testing my ecu would be easy. I was hoping to get a reply along the lines of " send it Joe Soap. he’ll test it for you, and charge you £ xx
What I have been able to determine is the following.
All of my fuses are O.K.
My multimeter, across the terminals of my battery shows a minimum of 12.5 volts.
My OBDII can not establish a connection to the ecu.
For both the crank position sensor and the cam angle sensor, where I would imagine I should find either 5 or 12 volts coming from the ecu, I only see 68 / 69 millivolts.

I am resigned to the notion that my ecu has given up the ghost, and will have to be replaced.


Go back a step (or 3).
The problem is your car doesn’t start, right?
When did it last run, and what has been done to it between then and when you noticed the non start issue?

I doubt you can check the signal from a CAS with a multimeter. You need a scope.

Correct Fred, the car does not start. it cranks over, but there is no indication of it wanting to fire up. In addition, when I am cranking the car, there is zero movement of the rev counter needle. From the research I have done I would have thought that, under cranking, I ought to be seeing 200 - 300 rpm. In fairness, Drumtochty offered to look into this, but I think I may have dropped off his list of “members I don’t mind helping”.

The last time the car did run was in July last year. Unfortunately, a long story, but I’ll keep this as short as possible, but this might be more than 3 steps.

I was having the AC gas recharged, on another car, at a local garage, and I mentioned a problem I was having on the MX5, a sort of flat spot between2,500 and 3,000 rpm. (I had posted about this issue on here, but I found no solution, other than a suggestion that I might have a timing problem.). The garage owner offered to take a look at my car, so I took the car the following day. The guy at the garage turned the key, revved the engine a bit and said “it sounds as if the timing is wrong”. As I had already bought the timing belt and water pump, based on advice from forum members, the garage agreed to fit the replacements the following day, if I supplied the parts. 

The next day, the garage fitted the new parts, but when the garage owner called me to tell me I could collect the car, he said that timing had been a part of my problem,( one tooth out,) but my biggest issue was very low or no compression in cylinder 4. I asked if he had performed a wet test, with a bit of oil in the cylinder to get some sort of indication as to where the problem lay, in the head or the cylinder. He said he had never heard of a wet test, and, as he basically wanted a blank cheque to work on the car, I collected the car and drove back to my place. Driving back, the flat spot was no better or worse than it had been previously. 

The following morning, I used the MX5 to do a quick run to the shops. The car started normally, and I drove off. About 100 yards from my place, the engine cut out, and has not turned over since.

So, the last time the car started and ran, more or less normally was the day after my timing belt and water pump were changed. Since then, I have followed the Haynes fault finding section for ENGINE ROTATES BUT WILL NOT START.

I have plenty of fuel.

The battery is properly charged.

The battery terminals are tight and not corroded.

My ignition components do not appear to be damaged, they are dry, and the ht coils show the correct resistance. The plug leads are brand new.

The crankshaft position sensor has been replaced with a brand new sensor.

I have found no broken, loose or disconnected wiring in the ignition circuit.

The spark plugs are new and correctly gapped.

All components of the fuel injection system have been cleaned and tested, and show the correct resistances.

The timing belt is brand new, and has been re-set correctly.

And, finally, I bought a compression tester, and with cold cranking, plugs in and plugs out, ( because the engine won’t run), i have  as near as dammit, identical compression across all 4 cylinders, and pretty much spot on with the original spec.

Apart from the fact that the car will not start, the most significant difference between now and prior to July last year, is that my OBDII will no longer connect to my car.

As I said earlier, in my reply to Robbie, I think i’ll surrender, and buy a new ecu.







Thanks for the suggestion. I’ll try and call him, on Monday.




A bit obvious but have you tried another OBDII reader?



No Paul, but I hooked up my OBDII to my other car, and, as there were no codes to be read, I switched to Live Data, and it functioned normally.




I’m aware that the timing belt has been replaced, but have you checked that it hasn’t snapped or slipped.

Are you ruling out the timing belt without inspecting it, on the basis that it’s been changed, so therefore its OK.

It’s seems very coincidental to me that the car should die soon after having it replaced.


I’m not saying it doesn’t happen, but I personally don’t know anyone, or anyone who knows anyone for that matter who had an ECU fail.

But I know lots who’ve had timing belts go.


Also, are there any plugs under the bonnet that maybe connect the OBD to the ECU, and maybe became dislodged during the timing belt change.