SOLVED! 2002 TB PCM bad 5v to tranny sensor

[rolo95]

Guys,
my 2002 TB tranny was doing strange stuff like hard shifting and late shifting when the engine gets to operational condition
when it is cold it works ok

so i take it to a tranny shop and they diagnosed that the temp sensor reads 300F instead of 160F even when the engine was cold
they said that the PCM line that goes to the sensor and suppose to have 5v , is giving around 2v when it gets hot
so they sad they need to replace the PCM, i am waiting for a quote,

Is there any recommendations to where to get a PCM fro my TB
i found this place that charges 99 for one but you need to tell them your VIN number so they flash it
no core swap, you can keep your old PCM
i do not know if that online seller is ok

any good places to get one ?

2002 Chevrolet Trailblazer EXT 4.2L GM Programmed Engine Computer number 12576463 | ECM ECU PCM |

Compatible with 2002 Chevrolet Trailblazer EXT 4.2L GM Engine Computer Number 12576463 Programmed to your VIN | ECU PCM ECM This listing is for one computer number 12576463 ECM PCM ECU (Engine control module) that is programmed for your vehicle using your V.I.N. (Vehicle identification number)...

www.flashmastersecm.com

 

[Mooseman]

It is unlikely it's the PCM as these have a very low failure rate. If it was the 5v, you would get errors from other systems as it is shared. One thing to try is unplugging the cooling fan clutch connector as it has been known to sometimes bring down the 5v reference when it fails (although mostly affects the throttle system). Then I'd check the wiring. Could also be a failure of the sensor that's affecting the 5v reference. It's part of the manifold pressure switch.

If you want to try a PCM anyway, grab one from a same year and gearing TB in a yard. No programming required. Just need to do the security relearn.

 

[TJBaker57]

With a cheap obd2 bluetooth adapter and an app like Torque or OBD Fusion you can see the two 5 volt reference circuits as well as the transmission temperature yourself! Could also be some bad wiring between the PCM and the Transmission.

 

[mrrsm]

If it helps... Here are the Class 2 Wiring Layout Schematics for the Trailblazers & Envoys...in Color:



Oh... Almost Forgot... Here are the Three PCM Direct Connectors Pin-Out to Wiring Diagrams...if needed as well:



Oh Well... What The Hell... Might as well throw in one for the BCM Class 2 Network Pin-Outs ...also in Color:

 

[rolo95]

Guys!!
Mooseman
TJBaker57
and
MRRSM
thanks so much for the info !!

MR :
what did you use to make your color schematic, love it !!
Many Many THANKS!!

BTW, i have a Tmobile syncup drive hotpsot (ZTE z6200) thingy that you plug in to the OBD2 port
will that work with torque or obd fusion,? i remember it can read the codes with the tmobile app
mmm...
i researched and looks like the ZTE although uses the ELM 327 protocol do not work with torque
i have an android phone
so i need to get an OBD2 reader, but there are lots of brands and some are clones that do not use the genuine elm 327 chip, they use clones that do not follow the command set correctly

any recommendations on a nice Bluetooth obd scanner for torque ?

 

[Mooseman]

Honestly, most of them will work, even clones. I've used the small blue ones and the bigger black, orange and blue ones. I don't think I've ever seen a real Elm327. I've had failures with both but will work initially. It's the longevity that's questionable. The V1.x seem to have better connectivity than the V2.x.

 

[rolo95]

what do you think of these ones

https://www.amazon.com/dp/B005NLQAHS/?tag=gmtnation-20

https://www.amazon.com/dp/B011NSX27A/?tag=gmtnation-20

https://www.amazon.com/dp/B00H9S71LW/?tag=gmtnation-20

 

[Mooseman]

The Veepeak I have two of. One failed, the other still working. No experience with the other two but the Bafx looks to be the same as this one, which I also have.

https://www.amazon.com/dp/B07CP5ZJVQ/?tag=gmtnation-20

 

[rolo95]

Thanks Mosseman ,i will get a Veepak

 

[mrrsm]

The serious Props for the "Colorization" belong to others... I just had to change my Google Search Tactics from using the "Web" option over to "Images" and then sift through whatever showed up on the screen. The PCM Connector images are courtesy TV... and the rest come from "GOKs" (God Only Knows) Where. :>)

 

[rolo95]

LOL!!! Thanks!

 

[Mooseman]

Those coloured schematics are actually in the manuals in my download link (in my signature)

 

[rolo95]

heads up
it was the computer, i got one on the junkyard for 20 bux, do you guys think i need to get one from flashers,com at 99 or keep this one ? anyway as soon the new PCM or ECM was installed and did the relearn procedure, the temps from the tranny read ok now as it should and the shifting come back to normal ( i did the filter change and refilled with oil like 2 months ago , no debris in the pan , no metal shavings actually i was like new, and no grime on the pan magnet, it was all clean)

Special Thanks to Mooseman
TJBaker57 and MRRSM for all the input and help

can you guys update the thread as solved ?
so to close this service ticket
All the best !!
Rolo.

 

[Blckshdw]

If the one you got solved your problem, there's no real reason to spend 5x as much money on another one IMO

 

[Mooseman]

Yep, no programming required.

 

[rolo95]

Thanks guys !
and one last observation

Mooseman said that before replacing the pcm, i unplugged the fan clutch connector, i did it and nochange, so i replaced the pcm,

BUT!!!! i remember that when my tranny symptoms started, i hear that the fan clutch and i mean the fan itself was making much louder than normal sound, i mean like a roaring fan sound when you run the blades at much higher RPM , so i thought that was caused but the clutch to completely engage so the fan blades were pushing too much air.

Anyway, that sound is gone, so i assume it was the PCM also that was wrong controlling the fan clutch

Now, this is the question, if the fan clutch itself is bad, it will fry my replaced PCM ?
so i need to change it ASAP or i can run like it is now, sounds ok, temp is normal
Rolo.

 

[Mooseman]

Not likely as it is controlled through a module (relay). It can short out and bring down the 5v but haven't heard of a PCM getting fried by it.

I guess as these trucks become geriatric, more issues that were previously unheard of are coming out.

 

[rolo95]

I guess as these trucks become geriatric, more issues that were previously unheard of are coming out.

Haa, it is the mandela effect, we are on a parallel reality now, thus all this unheard issues are starting to rise