noise from top end when tranny shifts - Mazda 6 Forums : Mazda 6 Forum / Mazda Atenza Forum
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post #1 of 5 (permalink) Old 10-07-2018, 01:02 PM Thread Starter
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Question noise from top end when tranny shifts

car is 2004 mazda 6 3.0L speed wagon with automatic transmission. less than 80K miles.

this one has me truly puzzled. if i am driving at slow speed....like through town...there is a very distinctive sound coming from engine bay each time the tranny shifts gears. the best i can tell, it is coming from the top end of engine( but origin of noise is difficult to determine since car is in motion, etc. ). The sound is similar to the "Cha-Ching" sound that people might make to imitate a cash register opening. A little lower in tone and more metallic. the car drives fine and is smooth at hiway speeds.

just to be thorough: i have been getting random misfire code for some time now...P0300. I do not know if this is related. i have been trying to resolve this misfire issue for a couple months now, to no avail. i tended to think these 2 issues are unrelated, as they did not initially appear at the same times. Thanks for any help you can throw my way.

2004 Mazda 6 Sport Wagon 3.0L Automatic
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post #2 of 5 (permalink) Old 10-07-2018, 04:02 PM
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Originally Posted by raleigh5 View Post
car is 2004 mazda 6 3.0L speed wagon with automatic transmission. less than 80K miles.

this one has me truly puzzled. if i am driving at slow speed....like through town...there is a very distinctive sound coming from engine bay each time the tranny shifts gears. the best i can tell, it is coming from the top end of engine( but origin of noise is difficult to determine since car is in motion, etc. ). The sound is similar to the "Cha-Ching" sound that people might make to imitate a cash register opening. A little lower in tone and more metallic. the car drives fine and is smooth at hiway speeds.

just to be thorough: i have been getting random misfire code for some time now...P0300. I do not know if this is related. i have been trying to resolve this misfire issue for a couple months now, to no avail. i tended to think these 2 issues are unrelated, as they did not initially appear at the same times. Thanks for any help you can throw my way.

If I had to guess I would say the shift noise is motor mounts. Start with the "dog-bone" trans mount at the bottom. Remember if the other two are torn it will stress the replacement mount excessively and lead to its premature failure. I replaced all three.


The random misfire code is deadly for your car
https://forum.mazda6club.com/members...l#vmessage9866
I would replace all coil on plugs (COP) and spark plugs immediately. The misfire will lead to catalyst failure and possible motor failure. Bite the bullet and do them all. If you cannot them all at least do the rear bank ones.
Yes it is possible to have a misfire (or shift noise)from another problem but it is significantly less common.


Good luck and ask questions if you need to.


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2004 6s Wagon 3.0, 5-speed ATX, Performance White (A2N)
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post #3 of 5 (permalink) Old 10-07-2018, 04:56 PM
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As said above, the misfire code is of paramount import to address quickly. I would replace all 6 coils and do your plugs while you're in there. The coils often show signs of unreliability right around the 100k mark give or take 10k miles. The repair now is cheap compared to the repair required if you don't address it quickly.

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post #4 of 5 (permalink) Old 10-07-2018, 09:58 PM Thread Starter
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thank you, i appreciate the replies.
i had already replaced all coils and plugs( correctly gapped ). also tested that all injectors are good; compression is good all around and engine vacuum is good. will definitely have the cats checked out, or just replace them.

Question: is it not possible to determine if the cats are bad by reading the various O2 sensor values and how they vary between idle and under load?
edit: as performed in this vid:

Good info on the motor mounts!

2004 Mazda 6 Sport Wagon 3.0L Automatic
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post #5 of 5 (permalink) Old 10-10-2018, 07:49 PM Thread Starter
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Took the mazda in and had the exhaust checked by a trusted performance exhaust shop. He gave it a thumbs up......no problems. I believe he based this on checks he did testing back pressure(?), exhaust flow.

He did present me with a few codes that my reader does not pick up. Though i am uncertain exactly how alarmed to be with these:
"U0101" - lost communication with TCM
"U0121" - lost comm with ABS control module
"U0155" - lost comm with instrument panel cluster control module.

I guess this is good news/bad news then. Back to searching for the cause of the P0300 random misfire.

2004 Mazda 6 Sport Wagon 3.0L Automatic
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