Cylinder Deactivation

[XR250]

Maybe TLDR.
I have a 2023 Mazda3 6MT with a 4 cylinder 2.5 engine. It has cylinder deactivation where it runs on two cylinders under certain operating conditions. It does this by energizing an oil control solenoid which pushes a pin out of the hydraulic lash adjusters causing them to collapse instead of the rocker arms pushing down the valves.
On the highway, it is pretty unobtrusive and provides pretty impressive fuel economy. Around town though, it is annoying AF. Anything under 2k rpm, it vibrates when in CDA mode. As such, I always find myself driving one or two gears lower than I normally would to keep the RPMs above 2,200 where it smooths out nicely. I typically would like to drive at 1,500 RPM's as the engine has no problem doing this and the "suggested gear indicator" always wants me there for best fuel economy.

None of the aftermarket tuners are able to access this part of the ECU to turn it off. As such, I took matters into my own hands by simply disconnecting the CDA solenoid electrical connector. Sure, I have a constant check engine light, but the car seems to just use the non-CDA map. It is like a completely different car now. So much more enjoyable to drive. I am actually getting better fuel economy as I can drive in higher gears around town without the annoying vibration of 2 cylinder mode.

So other than CEL, i see no downsides to this. I suppose if there is an unrelated fault, I will not know as the CEL is already on. However, I feel like that would be pretty apparent in the driveability.

Y'all have anything for me?

 

[XR250]

Im from Slovenia, far far away from you. Herr u have codes.

P3403 w/ the passenger side solenoid disconnected.

 

[XR250]

This is what the tuner said:

Ok! This is a CEL code that I have access to in the ECU to disable.
I'm now curious if disabling these codes would also disable the system. We've seen that occur with the active air shutters.

Have not heard back from him though.

 

[SwinnyGG]

Sounds pretty reasonable to me.

Will the system re-activate if power is delivered to the solenoid without an engine restart?

If so, I'd investigate putting a switch in-line somewhere in the cabin so that when you're on the highway and want the deactivation again for best economy you can just turn it back on.

 

[XR250]

I imagine it would. I don't want to hack into the harness until the warranty is out though. Is there a place that I can buy the connectors to fit the existing so I can make a sub-harness?

 

[SwinnyGG]

It would take some legwork but you could figure out the mating connectors and make a little sub harness to go between the engine harness and solenoid... You'd need to dig in to a Deutsch catalog.

 

[System Protection]

I've had this one bookmarked for awhile for the next time I needed a automotive connector: https://connectorexperts.com/

Have not used it myself.

Otherwise, I just use Deutsch connectors.

 

[XR250]

I've had this one bookmarked for awhile for the next time I needed a automotive connector: https://connectorexperts.com/

Have not used it myself.

Otherwise, I just use Deutsch connectors.

Wow, nice. They have a bunch but not showing one specifically for the CDA solenoid. I'll take some pictures of it and try to find some matches. Thanks

 

[BrianPetersen]

Intercepting the harness connector won't accomplish the desired task (assuming the desired task is to disable cylinder de-activation without having a fault-warning lamp and underlying code). Even if it contains circuit trickery to fool the system into thinking the solenoid is still connected, the on-board diagnostics are still going to be able to detect that it didn't accomplish the cylinder de-activation. It will just flip from a "circuit open or shorted to ground" type fault code, to a "system performance" code.

 

[XR250]

I am aware of that, Brian.

 

[Byakko]

Thanks a lot for the post

Any updates on the longer-term effects? Or issues

Got a new 2025 Mazda3 Sport GT MT, and the stupid thing is dropped 4cyl on coast and 2cyl while in gear one/two around stop signs and traffic lights

BS dealer said this only engages on highway speeds

From the literature, the ECM can't be modded by dealer and Mazda won't do it either by request, and perhaps tunes when it gets decrypted have no access to that area?


Definitely interested in the selenoid trick

Matt

 

[XR250]

Still have mine disconnected with no negative effects so far. Much more pleasurable to drive. Only have to disconnect one and it shuts the whole system down. I put a latex glove over the connector and plugged it partially back in to keep moisture out.
The gas mileage drops 1 or 2 on the highway but it is well worth it for me.

 

[Byakko]

Still have mine disconnected with no negative effects so far. Much more pleasurable to drive. Only have to disconnect one and it shuts the whole system down. I put a latex glove over the connector and plugged it partially back in to keep moisture out.
The gas mileage drops 1 or 2 on the highway but it is well worth it for me.

Thanks for the reply! I was thinking about protecting the connector pins with electrical tape or something. Glad to hear its been working out.

I'd probably re-engage if I take a road trip out the mountains, but hating this "feature" for city driving.

Seems so odd this would be on a top trim level Sport edition ffs. No Turbo with 6MT in Canada which is also nuts, and would have solved the issue as Turbo has no CDA


Cheers

 

[XR250]

No Turbo with 6MT in Canada which is also nuts

I don't think any Mazda3 turbo has a stick. The gearbox likely does not have the strength. Much easier for the computer to protect a slushbox. In the US, only one trim gets the stick - Premium.

 

[Byakko]

I don't think any Mazda3 turbo has a stick. The gearbox likely does not have the strength. Much easier for the computer to protect a slushbox. In the US, only one trim gets the stick - Premium.

Ahhh, I was wondering about that. Wonder if that puts a crinkle in my 3yr plan of buying a supercharger


Up here it's only Sport GT with stick and zero options available other than paint etc

 

[XR250]

Ahhh, I was wondering about that. Wonder if that puts a crinkle in my 3yr plan of buying a supercharger

I imagine if you don't drive like an idiot, it will be fine.