Check Engine Light - Knock Sensor

CX5_GC

Member
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Mazda CX 5
Hello all, and thanks in advance for any input.

We just purchased a new CX5 - Touring, FWD - literally three days ago. My wife has put 70 miles total on the vehicle, but today while she was driving the check engine light came on (yellow/orange) and she reported not noting anything remarkable about car performance. I picked the car up from where she was and drove it in to the dealership. They determined the knock sensor had gone off (I thought possibly in retrospect it seemed to accelerate a little less smooth than I had remembered in the test drive, but that could all be in my head).

It was toward the end of business hours today and they said it would be fine to drive it home and bring it in tomorrow. Apparently, one of the more advanced analyzers they link up to (or whatever computer program they utilize to further diagnose these issues) was down today, and will be back up tomorrow.

This seems like a bad omen and is a little more alarming than just a loose gas cap. Anyone else have any similar issues or have any input?
 
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Stuff does happen but, I doubt this is a "bad omen". Thinking back for the last 5 new vehicle I've bought and everyone of them whent back to the dealer at least once in the first 2,000 miles. 1980 Dodge, 1990 Lazer, 1995 Jeep, 2000 Subaru and my 2007 CX7. As long as the dealer takes good care of you, all should be good. Ed
 
Thanks for the input.

We've never owned a new vehicle before ever, so this was a little concerning.

I'll try to post back and update tomorrow after I get more info from the dealer.
 
You are the first to experience this problem here. Let us know what the outcome is please.

Should not be considered bad omen, even the best automakers will deliver cars with minor defects ( I've owned plenty of new cars to experience a variety of defects).
 
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You are the first to experience this problem here. Let us know what the outcome is please.

Should not be considered bad omen, even the best automakers will deliver cars with minor defects ( I've owned plenty of new cars to experience a variety of defects).

Thanks.

They had reset the check engine light last night and it went off on my drive home. When I restarted the car today it came back on. They are going to replace the knock sensor, but it's apparently deep in the engine and will require some time.

I've only driven the car 3 times now (test drives and once when I took it in), it's my wife's vehicle. With that said, it seemed start up a little loud this morning then quieted down after about 15 seconds. It appeared to be running without obvious knocking. So far after only ~90 miles driven our average MPG is only 24.5, with about a 50/50 mix of city/highway.
 
The loud cold start is normal for 15-30 seconds, try a search for details on the unique cold start.

Best of luck at shop today.
 
Thanks.

They had reset the check engine light last night and it went off on my drive home. When I restarted the car today it came back on. They are going to replace the knock sensor, but it's apparently deep in the engine and will require some time.

I've only driven the car 3 times now (test drives and once when I took it in), it's my wife's vehicle. With that said, it seemed start up a little loud this morning then quieted down after about 15 seconds. It appeared to be running without obvious knocking. So far after only ~90 miles driven our average MPG is only 24.5, with about a 50/50 mix of city/highway.


Just to help clarify about the "light" that turns on. Like CX-SV said there's a loud cold start of 15-30 seconds which (at least in our car) is accompanied by a light indicating the engine hasn't reached optimal temps. I believe this light to be either white or blue if I can remember. Could it be possible your wife mistaken it for the check engine light?

Also if it's indeed the yellow check engine light maybe a loose gas cap triggered it.
 
Just to update.

They apparently did a full computer download and then have uploaded the information. The dealership here doesn't have a great handle on the issue and "have sent all the information into the Mazda engineers." They'll have the vehicle for at least the full day today and possibly into tomorrow.
 
Just to help clarify about the "light" that turns on. Like CX-SV said there's a loud cold start of 15-30 seconds which (at least in our car) is accompanied by a light indicating the engine hasn't reached optimal temps. I believe this light to be either white or blue if I can remember. Could it be possible your wife mistaken it for the check engine light?

Also if it's indeed the yellow check engine light maybe a loose gas cap triggered it.

Yeah, I'm aware of the cold engine light. I personally drive the vehicle today and sure enough the yellow/orange check engine light was on again. I adjusted the gas cap and it stayed on. At the dealership both last night and this morning they confirmed with their computers that the knock sensor is being triggered. The question is now whether the engine is truly knocking (haven't heard frank knocking, but it didn't seem to be accelerating as smoothly or quickly as I had remembered from the test drive), or whether it's the actual sensor misfiring inappropriately.

Apparently, it's kind of a big undertaking to replace the sensor, so they're reluctant to just change it out if it isn't the root of the problem.
 
It isn't surprising, given the design/attributes of this engine.
High compression (by design), with very strictly governed fuel usage (for the sake of conservation), and heavy timing advance could potentially lead to engine knock under the right conditions. However, it seems as though it would take bad gas or a mechanical issues for this to happen with any frequency, on this particular vehicle.
Also, it is a tad unusual for the ECU to indicate an MIL for the use of its knock sensor. Input from the knock sensor is something the ECU uses very frequently as it attempts to continually modulate engine parameters.
 
Well rest assured that they will fix it. Back in Jan my wife's Mazda 3 developed a knock in the engine at 14k miles. They replaced the engine no arguments. I am a firm believer in Mazda and their product.
 
Thanks all for the continued input.

No further updates since I last talked to them in the late morning. If I hear anything further I'll let you all know.

If anyone is interested enough I can try to get specifics about computer diagnostics read-out if anyone is that interested. I personally know very little about cars, but I'm trying to educate myself.
 
Little update.

The service guy drove it and didn't see anything obvious. They sent the computer codes off to California for assistance in diagnosis. They too were unhelpful but forwarded on the information to Japan. They are calling me in the morning with any further updates.
 
CX5_GC - I assume they gave you a decent loaner car. And thanks for keeping us informed.
 
CX5_GC - I assume they gave you a decent loaner car. And thanks for keeping us informed.

I was offered one later today (not initially, they anticipated a quick fix initially), but I'm actually flying out early Friday morning to give a presentation at a conference. So my wife and I will just car pool for the time being, as our offices are pretty close to one another.

I'd rather them take their time and fix it correctly than hurrying it along for convenience sake anyway.
 
Are you still on the same tank of gas? Maybe try adding some octane booster? It could possibly be bad gas.

I thought about that, but it's actually the original tank that the dealership had filled up for us. As mentioned, we've only driven ~70 miles and still have 3/4 of the original tank left.

I don't know what the error codes are reading, but it sounds to me that it's something perplexing. They may suggest this to me, but for now they're wanting to keep it, drive it some, and see what the Japanese engineers have to say about the computer read outs.
 
CX5_GC - Are you having the vehicle serviced at MedCenter Mazda? If so, I expect that they will treat you right and eventually resolve the issue. We have dealt with them for years (including a transmission problem on our new CX-5, addressed in another thread in this forum) and though it took a few days, they got the problem fixed and we've had no further issues.

BTW, MedCenter Mazda is the dealer often referenced in this thread for great prices on accessories (www.mazdaparts.org).
 
CX5_GC - Are you having the vehicle serviced at MedCenter Mazda? If so, I expect that they will treat you right and eventually resolve the issue. We have dealt with them for years (including a transmission problem on our new CX-5, addressed in another thread in this forum) and though it took a few days, they got the problem fixed and we've had no further issues.

BTW, MedCenter Mazda is the dealer often referenced in this thread for great prices on accessories (www.mazdaparts.org).

Yes, it is Med Center Mazda. So far they've been good to work with and put our car as a priority on their garage. It's kind of funny because a couple of the service guys and salesman all bought (or leased CX-5's) because they like them so much, and they've been especially interested to see what's going on.

The Japanese Mazda team had them run more in depth computer analysis and it appeared the code was triggered during a deceleration period. They apparently recommended resetting some computer codes and then driving it around a bunch to gain more data, then plugging it back in to get more data. They're driving it around now and I will update if I get more info.
 
Update:

Please forgive me for any mangling of the scenario, but this is how I understood what they told me:

They have apparently discovered a small sliver of metal at or near the PCM box that served as a ground for a spark or short that was triggering the error codes coming from the knock sensor. They have removed the metal sliver and it appears to be running well now. They're sending someone to pick me up soon.

After I drive it I'll report back if anything is awry.
 
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