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'05 TB 4.2 EXT
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Discussion Starter · #1 ·
Well --- almost three years into code P2122, I finally found the trouble maker ... the sto-o-o-o-pid fan.

Naturally - after running an oscilloscope on the throttle rheostats and checking both resistance ramps and the mysterious "Null Point" --- I dismissed the foot throttle (APP) as any reason at all for the code; everything was right where it needed to be.

I suspected something was taking a hit off the 5V power supply from the ECM but I couldn't prove it since it was so intermittent ... the fan was never in my suspicion.

The P2122 OBD-II trouble, or fault, code means that the vehicle's on-board computer has detected low voltage in the throttle position sensor (TPS), which is usually below 0.17 volts. Code P2122 is defined as a Throttle/Pedal Position Sensor/Switch "D" Circuit Voltage is Low
....

... this is not the whole truth although it DOES run off the available 5VDC system coming out of the ECM.

The final clue was that the fan decided all on it's own to go into MAX-ON Mode.
The roaring told me all was not well and I got the P2122 instantly - it refused to clear until the fan speed dropped into a more-or-less normal RPM and I got to drive away at that point.​

Here's the sketchy part ---> I cannot find a decent fan assembly and I have to install a brown box, house brand fan from O'Reily's.

I'll be posting the success or failure of this fan - and that might be fun to help debunk or support the nay-saying about off-brand parts.

(OK --> I didn't say to use off-brand spark plugs. That would be bad.)








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2004 chevy trailblazer_lt
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Congrats! If the fan you got at O'Reilly's was branded Murray, there is a very good chance that it was manufactured by Four Seasons/Hayden which I am sure you are aware are brand names of SMP.

My fingers are crossed for it being the cure!
 
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'05 TB 4.2 EXT
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Discussion Starter · #3 ·
Congrats! If the fan you got at O'Reilly's was branded Murray, there is a very good chance that it was manufactured by Four Seasons/Hayden which I am sure you are aware are brand names of SMP.

My fingers are crossed for it being the cure!
Tomorrow --- if it's not actually snowing again --- I'll go out and change it.

I MAY have to drive my '86 K5 for a day or so until the melt-off.
 

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2004 chevy trailblazer_lt
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I'm sure you won't like that. :D
 

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'05 TB 4.2 EXT
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Discussion Starter · #5 ·
I'm sure you won't like that. :D
Oh no ---- I like to drive the K5. Maybe I'll try to find a way to duct tape a camera inside it anfd take it for a ride and video some of where I live.

It might make it to YT.
 

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2003 chevy trailblazer_ltz
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Pretty sure my Trailblazer has an O'Reillys fan on it. Been so long I forgot where I bought it...

Louder at start-up than the previous fan. Whether that was because the previous fan was worn-out, I don't know. But either it's settled-down some, or I've gotten used to it. Doesn't seem to be as loud at start-up as it was.

I put that fan on when we still lived at the "old" house; we've been at the "new" house for over five years. So that O'Reilly's fan is maybe seven years old now.
 
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Discussion Starter · #7 ·
Pretty sure my Trailblazer has an O'Reillys fan on it. Been so long I forgot where I bought it...

Louder at start-up than the previous fan. Whether that was because the previous fan was worn-out, I don't know. But either it's settled-down some, or I've gotten used to it. Doesn't seem to be as loud at start-up as it was.

I put that fan on when we still lived at the "old" house; we've been at the "new" house for over five years. So that O'Reilly's fan is maybe seven years old now.
Good t'know!

It's lightly snowing and that seems to affect my attitude about working on the TB today. But ---> I KNOW I have to, so this is rapidly not becoming an opt-out option, if you know what I mean.

Most fluidic driven fans - it matters not if it's also electric, if it has those clutches and a heavy-ish viscous fluid between them --- will make a lot of fan noise at cold start-up.

If you want to really hear fan noise at cold start, try a Hayden HD fan for a SBC! It'll scare you (Code: BROWN) the first time you install one. BT ---> DT!
 

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When it was me, I used the fan-clutch wrench set that's part of the O'Reillys loaner-tool program; the 36mm unit was what my '03 needed. Remembering this confirms that I bought the fan clutch at the Big O. Most likely a "Murray".

A bigass adjustable wrench works, too, but is cumbersome and substantially heavier.

Regular threads, not "reverse" threads. Seems to me that figuring-out the electrical connector, and the fan shroud were the worst parts.
 

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Discussion Starter · #9 ·
When it was me, I used the fan-clutch wrench set that's part of the O'Reillys loaner-tool program; the 36mm unit was what my '03 needed. Remembering this confirms that I bought the fan clutch at the Big O. Most likely a "Murray".

A bigass adjustable wrench works, too, but is cumbersome and substantially heavier.

Regular threads, not "reverse" threads. Seems to me that figuring-out the electrical connector, and the fan shroud were the worst parts.
I've hardly ever used the B.A. wrench ..... instead I used an air chisel and just popped it on the top of the hex and spun it a bit - then it came off easily.

It never seemed to affect the water pump - although one would think so. But it didn't. Of course I never kept whacking on it --- if the air chisel didn't do it in just a couple of hits - it was time for matching Channel-Locks.
 

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Discussion Starter · #10 ·
Well --- in the interest of honesty --- I STILL wanted to see it (the fan) malfunction ... and throw the crazy P2122 code --- which is NOT related to it in any but one way --- the 5V rail voltage!

In my testing --- (and not yet replacing) --- I noticed some bad juju on the 5V line in the APP, but ONLY when there was some notable hash on the Fan Speed SENSOR!

Hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm.

How in Hell's Bells can a fan Speed sensor throw a P2122 code?
I would be happy if it was/were a P060E or sumpthin' like that.

This is odd. How much hash is also floating in the rest of the 5V line?

Imma should just change the fan and drive the sukkuh --- but I still want to KNOW .... ya know?
 

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Discussion Starter · #12 ·
More questions ----

Since the fan has locked into direct drive --- prolly the internal clutch assy jammed and locked it all together --- now I can run Cruise Control with no problems with no more P2122.

OK --- since we know the fan was going bad and was killing the 5V power - what about the fan is not reporting that it's locked into full speed and hasn't tripped a different code?

Is there a code for "overspeed" of the fan?
 
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