Engine making a whining sound, check engine light turns on and seems to go into limp mode

  • 2007 MAZDA DEMIO
  • 1.3L
  • 4 CYL
  • 2WD
  • 89,000 MILES

I’ve had trouble with the check engine light since buying my car mid-last year (2020). I’ll try and break it down and hopefully someone might have a suggestion!

Check Engine Light - I took my car back to the dealer about 4 months after purchase. Mechanic checked the computer and the engine knock sensor had triggered. There was no knock, so the sensor was reset. The check engine light stayed off for a while but eventually the knock engine sensor was triggered again so the mechanic replaced the sensor. This did the trick for a while, but it seems the problem has returned, with the same issue - sensor triggered but no knock. The check engine light can turn off from time to time, but it is typically on as soon as I start the car.
Limited go - the more recent check engine light/sensor issues have been accompanied by some kind of “limp mode”. It’s worse when it’s cold and worse when trying to head uphill shortly after turning the car on. This is where, regardless of how much I push the pedal; the car just won’t go above 30km/hour? Maybe 40km/hour? Occasionally a bit of acceleration will get through but only for a second. Then, after maybe 2-3 minutes, it will kick in and the car will drive as usual. I haven’t spoken to the mechanic about this as I haven’t been able to book in since the sensor was reset last.
Whine - when accelerating, I can sometimes hear a high pitch whine. Not always and usually only if I accelerate with speed. It sounds like a whistle.

Other things to note, I got the serpentine belt replaced shortly after getting the car (so only a year ago), I’ve recently ran an engine cleaner through the fuel (petrol), last service was June 2021, but no oil change was done.

I hope I’ve explained that well enough. I’m not sure if the issues are related so I’m hoping for some advice on if it could be connected to one problem or if it’s more likely that lots of things are buggered.
Thanks in advance. :)
Do you
have the same problem?
Wednesday, October 6th, 2021 AT 11:21 PM

1 Reply


This vehicle isn't offered in the US, but I'll try my best to help.

First, the knock sensor is designed to fine tune the ignition timing. This prevents valve ping and improves the vehicle's performance. If it is bad, there could be an issue with timing itself, so we really need to have the computer scanned for diagnostic trouble codes. Here is a quick video showing how it's done:


If you own a scanner, do that, and let me know what codes are stored. If you don't, have it done and let me know what is found.

Next, the description you provided leads me to think it could be a couple of other things. For example, low fuel pressure or even a partially plugged catalytic converter.

Take a look through this link. It describes common symptoms related to a plugged catalytic converter.


If you want to check the fuel pressure to make sure it isn't low, here is a link that explains in general how it's done:


Let me know if this helps or if you have other questions.

Take care,

Was this
Thursday, October 7th, 2021 AT 6:43 PM

Please login or register to post a reply.

Sponsored links