Mazda 3 ECU swap question

[newguy90]

Hello,
(sorry for thread hijacking)
I have the same issue with the same ECU on the same car.
Trying to put hand on some wiring diagrams, especially ECU pinouts (as I only have the ECU for repair right now).
Thanks a lot if you can help.
Be sure I'll keep you informed if I solve the problem.

EDIT : Mazda dealer service told : "no power to fuel pump => ECU"
I'm not aware of any DTC he might have found

What do you mean by "same issue"? Car cranks but doesn't start? When you turn the ignition to ON, do you hear the Fuel pump working ?
Can you explain your problem in more detail?
If you need the wiring diagram of the mazda 3 , you can find it in my #10 message from this post.
From the wiring diagram you can see that Fuel Pump relay (K20) gets its power directly from the car battery through F24 fuse, and it feeds 12V to the fuel pump.
ECU is controling the Fuel pump with the help of the Fuel pump relay (ECU grounds the fuel pump relay). This is done by ECU through 1AC pin .

You must check the continuity / short to ground/ short to power of the fuel pump. I attached a document from the Mazda Workshop manual for you (FUEL PUMP UNIT INSPECTION [ZJ, Z6, LF]).

[electronico]

Hello,

Thanks for your inputs !

I came back to car.
Fuel pump relay is well activated and fuel pump 12v supplied.
Engine cranks, but no start.
Supplying a 12V on PCM 2T pin allows car start.
I'll enquiry about PCM, trying to fix it.

[newguy90]

Then why did your mazda dealer say that your car's pump fuel it's not powered ? (your Mazda dealer service told you : "no power to fuel pump => ECU").
So you don't have any power on 2T ECU pin? That means you have indeed the same problem like I have. Not only 2T has no B+, like it should, but also 2BG, 2E, 2F, 2G and 2L of the ECU pins. As far as I know, all those pins are connected to each other, so the ECU doesn't feed 12V (or B+) to the MAF, EGR, HO2S1, HO2S2, EVAP, and fuel injectors. ... Can you confirm that?
What voltage do you have on pin 1AB and pin 1P when the ignition is ON? Also, can you tell me what's the electrical resistance between 2T pin and 2BH pin of your ECU (measured when ECU is disconnected)?

[electronico]

Then why did your mazda dealer say that your car's pump fuel it's not powered ? (your Mazda dealer service told you : "no power to fuel pump => ECU").
So you don't have any power on 2T ECU pin? That means you have indeed the same problem like I have. Not only 2T has no B+, like it should, but also 2BG, 2E, 2F, 2G and 2L of the ECU pins. As far as I know, all those pins are connected to each other, so the ECU doesn't feed 12V (or B+) to the MAF, EGR, HO2S1, HO2S2, EVAP, and fuel injectors. ... Can you confirm that?
What voltage do you have on pin 1AB and pin 1P when the ignition is ON? Also, can you tell me what's the electrical resistance between 2T pin and 2BH pin of your ECU (measured when ECU is disconnected)?

I can't tell for the Mazda dealer, that's what he told to the end-user.

Yes all these pins are connected together on the ECU.
I have brought only the ECU back to bench, so can't measure anything on car right now.
2BH is GND and I read infinite resistance between 2T and 2BH, which is normal.

Up to now I haven't found any destination on ECU for these 2T - 2E - 2F - 2G - 2L - 2BG pins, so I wonder if these B+ missing line isn't wired out of the ECU.

Looking at the schematic, pins 1BB - 1BC - 1BF - 1BG should be connected to B+ but they are not on the ECU itself.
And this B+ line goes to Vehicule Speed Sensor too.

Next week will be off for me, so next tests on August 24th.

[newguy90]

I can't tell for the Mazda dealer, that's what he told to the end-user.
2BH is GND and I read infinite resistance between 2T and 2BH, which is normal.
Up to now I haven't found any destination on ECU for these 2T - 2E - 2F - 2G - 2L - 2BG pins, so I wonder if these B+ missing line isn't wired out of the ECU.
Looking at the schematic, pins 1BB - 1BC - 1BF - 1BG should be connected to B+ but they are not on the ECU itself.

Hm.. Now I'm confused... My old ECU, which is on the car now, has infinite resistance between 2T and 2BH pins, but my new ECU which I bought to replace the old one shows 0.775 ohms when I measure with the multimetre set on 2 Kohms reading!
If you say infininte is good, then colud my new ECU be bad?? I'm lost.


About the 1BB - 1 BC - 1BF- 1BG ... NO, they don't have to be all connected to B+, because 1BC and 1BG are for the automatic shift version of Mazda 3, not for the manual shift version.

You said that B+ line goes to vehicle speed sensor? Do you mean CKP sensor? Or the speed sensor inside Instrument cluster?

I am taking a short vacation too for the next 10 days, so good relaxation to us.... and to all others who need it .

[narkeleptk]

Hm.. Now I'm confused... My old ECU, which is on the car now, has infinite resistance between 2T and 2BH pins, but my new ECU which I bought to replace the old one shows 0.775 ohms when I measure with the multimetre set on 2 Kohms reading!
If you say infininte is good, then colud my new ECU be bad?? I'm lost.

Your "new" ecu is completely different hardware from your old one if its the same pictures you posted, you would not be able to compare them.

[newguy90]

I hope you're right, narkeleptk! 😁

[electronico]

Hm.. Now I'm confused... My old ECU, which is on the car now, has infinite resistance between 2T and 2BH pins, but my new ECU which I bought to replace the old one shows 0.775 ohms when I measure with the multimetre set on 2 Kohms reading!
If you say infininte is good, then colud my new ECU be bad?? I'm lost.

About the 1BB - 1 BC - 1BF- 1BG ... NO, they don't have to be all connected to B+, because 1BC and 1BG are for the automatic shift version of Mazda 3, not for the manual shift version.

You said that B+ line goes to vehicle speed sensor? Do you mean CKP sensor? Or the speed sensor inside Instrument cluster?

The model I work on is an automatic shift version.
You're right, it seems Vehicule Speed Sensor is only for ATX (Automatic Shift).

I am taking a short vacation too for the next 10 days, so good relaxation to us.... and to all others who need it .

I have attached the PCM (ECU) wiring diagram I found.
Strange thing (for me) is :
- Why is the B+ line called :
'i' on pins 1BB 1BF 1BG
'e' on pin 1BC
'g' on pin 2BG
There must be things between them, or they would be called by the same letter.

Attached on-board diag through radio, mainly because I can't see any default (they have been cleared by previous techs) with my generic VCI, I'll test this ASAP.

[electronico]

So :
Wiring a 10A fuse between ( 1BB 1BC 1BF 1 BG ) and ( 2BE 2BF 2BG 2L 2T ) allows car start.
Car seems to be in degraded mode with MIL lit (4000 rpm max).
I should have car at end of week to test better.

[newguy90]

Hello! I'm back from the vacation... So let's get to work.

Strange thing (for me) is :
- Why is the B+ line called :
'i' on pins 1BB 1BF 1BG
'e' on pin 1BC
'g' on pin 2BG
There must be things between them, or they would be called by the same letter.

Those things baffled me too at first glance, but I realized they are indexes of the connections (the Mazda guy didn't want to over_lap lines in the diagram )
So, the "i" on pin 1BB, 1BF, 1BG is actually a "f" (poor graphic file) and indicates that is connected to the"f" from Main Relay and Fuel Pump ( a bit lower and to the right on the same diagram page).
The "e" of the pin 1BC indicates that is connected to the VSS terminal noted with the same letter "e" .
And, lastly, the "g" on the pin 2BG is connected to the "g" terminal of the MAF Sensor.
I attached the two pages diagram modified by me, if it helps.

Attached on-board diag through radio, mainly because I can't see any default (they have been cleared by previous techs) with my generic VCI, I'll test this ASAP.

If the trouble codes were previously cleared, you won't find them anymore. But if you want to replicate them, then all you have to do is :
1) turn the ignition to ON,
2) feed B+ from the 1BE (IG1 = ignition) to both (or at least one) of the output lines (2T / 2BG),
3) turn the key to start the engine (the engine should start, and run without any issues or DTC's - at least my car's engine works fine, and it revs without any issues - it doesn't lit the MIL and no rev limitation, until the 6500 rpm, of course)
4) while engine running, disconnect the feed line connected as indicated at step 1). When you remove the B+ feed line, the engine will stop, and the following DTC's will show up: P0031, P0037, P0102, P0403, P0443.


NOTE 1: Don't run the engine for long periods if you connect the B+ feed to just one of the output lines (2T/2BG) or you may burn the circuits inside the ECM due to overloading.


NOTE 2: If you encounter errors when you power the car using a B+ feed line like I told you above, and the MIL is lit, read the DTC codes and let me now what you have found.


p.s. When you will have the car for testing, can you verify also the voltage you get at pins 1P and 1AB (with the ECM connected) as I previously asked you? The mazda workshop manual shows B+ at those pins, but my car has only 5.91 V! Thanks!

[electronico]

Hi,
Sorry for the late reply,
I should have had car for testing this week-end, but I had to schedule to next one because of urgent works.
Be sure I'll let you know how it goes.
Customer complains mainly with bad automatic shifting and power lack (this last felt by me while testing).

[newguy90]

How are you , electronico? Did you managed to test the car yet?

[electronico]

Hi, I have the car, but have many urgencies to deal with before having a look.

[electronico]

Well,
Forcing B+ to 2E went OK.
2E is wired to 2BG on ECM.
Car was well running as usually.
After 40km drive, the 2E to 2BG track fused.
Replaced it with a thin wire : blown again.
Wired a 20K resistor between 2E and 2BG : still got 0 Volt at 2BG.
2BG is for sure the problem.

About your asks,
1P was 4.91V
1AB was 6.91V
(automatic shift)

I gave up and loose 2 days of work on these, won't see car again.

[Meat-Head]

So either something silly like lamda sensor rubbing once in a while to earth or something
simular, sounds like second time it’s blown a hidden track as your thin wire was too ‘thick’

great To read about stuff like this, nice when car comes in the same and great for pub quiz question

thanks