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Discussion Starter · #1 ·

G'Dayall
Well if you have been following the engine bay sound threads, some of you willknow I tracked that sound down to the Transmission Control Module. Knowing itslocation and giving my best technical guess at it being one of the transmissionsolenoids, it was off to GM in the USA to get the technical reason for thissound.

With a very nice return email from them, they asked me to contact Holden backhere.
This is where the loop starts.
Holden Head Office, advised me to contact a Dealership, the Dealership asked meto contact Holden.

So after I forwarded the email from the parent company GM back to Holden, theyadvised they would do a little research.

Today I got the call following that research.

That sound is "classified". I kid you not!
Holden advised they were unable to release that information to a customer, whojust happens to own the item...
So I guess in a world of IP, TM and Copyright, Holden and GM are keeping thisunique sound under wraps.

Still, give it a few years and it will be on ITunes for the world to enjoy.

I'll have to use this at work next time I'm asked by aircrew, "whats thatsound in the engine nacelle?"


 

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Interesting. Are you sure it's the transmission? I too have had that high pitch electrical noise, but my transmission's a manual.

Kinda weird they won't say anything.
 
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The MTs also have the Transmission Control Module - it's just programmed differently.
 

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"Classified" usually means "I don't know", or if military "I don't want you to know".
 

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Don't forget the government's other definition of "classified" - "I'm embarrassed to let anyone know I'm such an idiot."
 

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The MTs also have the Transmission Control Module - it's just programmed differently.
Are you sure? There is no listing of a module in Service Information.. nor have a seen one.
 

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OK - I may be wrong. What's controlling the red-line engine limiter then?
 

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The ECU controls everything in a MT car. There's no transmission computer on a manual car.

The ECU is usually programmed differently for a MT car. You will notice that the Cruze has a "rev hang" when you shift, and bumps up RPMs when you let the clutch out in neutral. The MT Cruze also hits full boost at 2500 RPM rather than the 1850 RPM AT's do.

My theory is that it's the expansion valve in the AC system. They are known to "squeal" at times.
 

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Discussion Starter · #10 ·
chevrolet_100317939_m.jpg

Good theory, and it could be the case with a gas bypass type of sound.
However, after locating it within the transmission outer black plastic cover, I'm sure its not the AC system.
That is, unless my tranny oil is cooled by heat exchangers and a very classified AC cooling system.
 

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Discussion Starter · #11 ·
Transmission Control Module
A 32-bit transmission controlmodule (TCM) monitors transmission performance and compensates for normal wearin components such as clutch plates, so transmission performance remainsconsistent for the life of the transmission. The control module also “tests”the components of the transmission following assembly to optimize theinteraction of the components.

The TCM is mounted inside thetransmission, where temperatures remain mostly constant compared to an external-mountedmodule. It is small in size, which helps minimize the overall size of thetransmission. The transmission and module are assembled together, so noadditional connections are necessary during vehicle assembly.

TECHMThe 6T40/6T45’stransmission electronic hydraulic control module (TEHCM – pronounced “TECH-im”by engineers) contains basic software and algorithms shared among allHydra-Matic six-speed variants, including RWD, FWD and AWD. The module islocated inside the transmission, which reduces manufacturing complexity, andrequires only vehicle-specification calibration to the core program. The TECHMalso enables features such manual shift control and grade logic.
 

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That is, unless my tranny oil is cooled by heat exchangers and a very classified AC cooling system.
GASP! You discovered their secret!!!

Quick, run and hide before the black Suburbans show up...
 

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Can somebody explain to me why, when the noise has stopped after the engine has been off for a minute or so, the noise starts again if I lock or unlock the doors with my remote?
 
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I haven't heard this sound since last summer. Just heard it again last night, when I shut the car off in the garage. If you key the car back on, and off, it is gone. It sounds like an energized solenoid or transformer to me. Some cheap HID kits I've had in the past, made similar noises. It is definitely electrical.
 

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When opening the hood Ive had heard this noise. Sounds to me like a purge of some sort.
 
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