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Mazda 6s check engine light

I need some help I have put a 2005 Mazda 6s motor in my 2004 Mazda 6s and now my cel keeps coming on with code “loss power to control module” I tried to get the ECU out of the other vehicle but it was too late it was crushed!!:frowning: is there any way to fix this please any help would be great full

How long since the swap? Which engine? Did it occur right away? What actual code are you getting in the format P0123? Which engine wiring harness did you use, the 2004 or 2005?Are there any connections on the engine that don’t exist on the wiring harness? Or vice-versa?

You are using the 2004 ECU, it shows a different ECU for 2004 and 2005 on RockAuto (4cyl). Neither are available, anyway but that is a big hint that they are not interchangeable.

Short of understanding the difference between the 2005 engine and the 2004 engine by comparing wiring harness pin-outs, it is unlikely you’ll ever get this solved.

Okay here’s what I did I took the old intake, injector’s, throttle body the whole top of the motor and put it on the new block so the wiring harness and fuel line was the same. What it’s doing is from a start acts like it’s in limp mode until it gets to about 3 grand then it opens up like it should but another wierd thing is on the highway I don’t feel any loss of power and I forgot to write the code but I do know that it said lost power to control module thanks again for the reply and the ingredients helps at this point

Oh and it’s the 6cyl 3.0L. it did not happen right away either it was after about 200 miles. Also the motors are identical I don’t have any extra plugs on the motor or the harness

That is a significant hint. All was well at first, but not now. I would check the electrical system - battery and alternator just to be sure they are not your lack of power. Having the code would answer which is the power control module. The Mazda 6 has several computers so that would narrow down the search. I’d check the ECU wiring first just to make sure you didn’t damage a wire with the engine install. Hook a voltmeter to the power pin on the ECU and drive it around to make sure it is consistent.

The fact that the engine runs OK at 3000 rpm up seems to point to an alternator issue. Good Luck! Post back with what you find.

Alright it’s coming along I think the old motor had bad valves I think that was throwing oil down bank 2 if that makes any sense. Well with the newer motor I think now my pre cat on bank 2 might be bad what’s your opinion should I get a new pre cat or just swap the o2 sensors The codes I had last night when I checked it was p0431 p0171and p0174 in that order but p0174 was pending I was thinking that the pre cat was bad because of the problem with the old motor but the pre cat is around 600-700$ and the sensors are about 100$ a piece please give me some advice on this subject I have put allot of money into this car just trying to get it to pass emissions and my last day on my temp tag is friday. Thanks for your time

Adam Valerio

Just swapping sensors won’t solve the problem of a bad cat and you will still fail an emissions inspection. That just affects the P0431 code and neither of the others. Both the others are lean fuel condition on both sides of the engine and a reason for that code needs to be found. I’d suggest pressure regulator is bad as long as my earlier suggestion of making sure the electrical system checks out. Low voltage to the fuel pump could give low pressure to the regulator and a lean condition to the engine.

Passing inspection Friday does not look promising.

When I got off of work I swapped out the o2 sensor I had in my car started it and heard a huge vacuum leak coming from my pressure regulator I fixed it but the cel is still on I pulled the positive of the battery and held the brakes till all my lights were off but the cel never went off??? Did I do that wrong?

Yep, you did. Your throwing parts at a problem instead of finding out what the problem is.

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Those are almost always a vacuum leak, check and double check all the vacuum lines, including PCV valve and brake vacuum booster line.

Could also be your intake manifold gasket(s)

With a vacuum leak your computer is telling the injectors to dump more fuel into the engine which could possibly give you the p0431

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Yes, you did it wrong

Congratulations on finding the apparent cause of P0171 and P0174

The preferred way to clear codes is with a scanner . . . or at least a cheapo code reader

If you want to disconnect the battery, remove the negative first, NOT the positive

But like I said, clearing codes is best done with a scanner, not disconnecting the battery

P0431 seems to indicate the warm up efficiency of pre-cat Bank 2 is too low . . . I’d say some more diagnosis is in order

You have almost zero chance of passing an inspection on Friday, in my opinion

Your car is new enough, so it probably won’t go on a dyno, and there will be no tailpipe test. But the inspector will still look if the check engine light is illuminated. And he will also check if you have the appropriate readiness monitors in a “complete” status. In many states, the catalytic converter readiness monitor must be complete, or the car fails.

Best thing you can do is google obd2 drive cycle procedures and try to follow them to the best of your abilities. Then use a scanner to check if all of your readiness monitors are “complete” . . . it’s quite likely you’re allowed to have one incomplete monitor, but the cat monitor has to be complete.

By the way . . . we have no idea what state you’re in. Does the inspector hook up to the car, or merely see if the check engine light is on at idle? It can vary widely, depending on where you live.

Oh okay that makes sense I’ve taken the intake plenum of more times than I can count so replacing them gaskets would probably be best. Andto add I pretty much just took the block I had to switch out the intake and injector’s cause the 05 motor didn’t have a pressure regulator on the fuel rail like the 2004

you reused the plenum gaskets when replacing the motor . . . ?!

You should have replaced them. It could also be a contributing factor to P0171 and P0174. But it depends. If they’re no longer able to seal properly, they were quite likely a contributing factor.

That suggests that the 2004 and 2005 motor . . . and maybe the car itself . . . had significant differences

Lack of a pressure regulator on the fuel rail for the 2005 motor suggests it’s designed to be used with a returnless type of fuel system

And if your 2004 motor had a pressure regulator on the rail, it’s a more conventional, return- type of fuel system

Those are significant differences right there, and there may be more, which we’re not aware of, and which you might not even be able to see

If you left the vacuum hose off of the fuel pressure regulator, that would result in higher fuel pressure, which might itself cause some problems

Is that what happened, or was the regulator itself somehow leaking?

What about the inspection procedures . . . ?!

What happened last time?

The hose on the regulator was cracked so I cut it and re connected it and the block was identical to the 2004 the only difference was the fuel pressure regulator every mount and sensor was the same I had problems with the pre cat on bank 2 last time with the old motor but I found one at the junk yard and reset my light drove it till my emissions was ready and got it to pass by the skin of my ass