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Randall
Randall, ASE Master Tech
Category: Transmissions
Satisfied Customers: 12744
Experience:  ASE Master Tech, 32 yrs, Auto trans diagnostic and repair
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I need a help with replacing the transmission trailblazer

Customer Question

Hi experts, I need a help with replacing the transmission for 06 trailblazer 4.2L 4x4 Automatic. Junkyard told me 05-07 4.2 4x4 transmissions will work for my truck. But can you tell me the difference between mine and 03 and 04 transmissions? Are the case,
gear ratios and shafts the same as long as it's 4.2 4x4? I don't mind swapping bolt on parts at all. Thanks for your help!
Submitted: 1 year ago.
Category: Transmissions
Expert:  Randall replied 1 year ago.

Hello, it is not so much about hard parts, case, shafts etc it is about trans controls, The solenoids, , sensors and switches internally are much different between the 2 trans missions, You just cna not use any except the years you were told, others? sure they will fit but the PCM /TCM computers, wiring etc and shift controlling is very different than the 05-07 , you must find this range of trans years

Customer: replied 1 year ago.
cool. how about 2x4 transmission? According to some sources, only the end shaft is different (requiring removing all internals to swap output shaft). And the a transmission re-manufacture company listed 2x4 compatible from 03-08. AC delco listed the valvebody same from 03-07. Other sensors are speed sensors, neutral switch that are bolt-ons? valvebody is not bolt on but easily accessible once the oil pan is out?
Expert:  Randall replied 1 year ago.

I can not answer about 2x2, I think the output shaft is the difference, I have never been asked to chage one on this trans from 4x4-2wd vs versa. Yes,, you would have to swap out the valve body to converty between older years and current,All I can confirm is 05-07 is the same and prior is not and looking at diagrams of electronics, this is where the problem lies, They are not the same from older to newer, sensors etc are bolt ons per say but most all incorporated in the valve body, Hard to explain, I do know the trns part numbers are one digit difference between 4x4 and 2 wd and about a $ difference so sure it is all about the output shaft

Customer: replied 1 year ago.
AC delco (OE?) listed the valvebody the same 03-07. And rest of the switches and sensor are easy bolt-ons (if they're different). The only thing left is the wiring harness and connectors. Maybe that's the main difference.I'll pull some factory diagram and let you know. it seems you're busy
Expert:  Randall replied 1 year ago.

not busy, It just takes a bit of time to pull up each of the various years and configs etc, I can honestly say, the wiring harness is different computer is different and trans controls are different per you original question, I know you added on about the add;l years and 2 wd, this is where it becomes a bit foggy, I was/am working on the 03 vs 05-07 I have all those diagrams and they differ in a big way between them, Sure solenoids bolt on etc , but all are internal on the valve body, The case, internal hard parts as mentioned prior are the same between the years / etc

Customer: replied 1 year ago.
06 transmission has 3 connectors: Neutral switch, c175, and c310(vss). C175 is the main one. The others are easily swappable. Although I still need to research the parts compatibility to be sure.There is no difference between 2003 and 2006. Pins are all the same, even circuit no. and functions are the same. They both are 13pin.If the valvebody and c175 are the same, then are we missing something else?As long as you can point me to the right direction, don't worry about spending time on research. I'm happy to do that to save you time.
Expert:  Randall replied 1 year ago.

I have all of this on my end as well, I do know for a fact wire colors are different at the plug, and they should both be 20 poin plugs, maybe onl;y 13 used, Not looking, I agree but wiring diagrams and pin numbers at the TCM are not the same, That is the first red flag, If you have all the connectors, do you have the wiring diagrams so you can see what I speak of?

Customer: replied 1 year ago.
it's technically 20pin connector but has only 13 pins in them. ECM and TCM are integrated. Pins are different at the ECM but wiring colors are the same. They may have updated the ECM for additional engine sensors and rearranged the ECM pins. This is necessary as different or more chips are on the circuit board and good circuit board design is far more important than keeping the same or similar pin arrangement. (possible CAN upgrade comes in mind).For example PC solenoid valve high control is a Rd/Bk wire in circuit 1228. This circuit goes to connector 2 pin5 at 2003 ECM but connector 3 pin6 at 2006 ECM. Same colors. I checked with at least 5 other circuits with the same positive results.It's worth mention the C175 connector table (GM published Doc ID(###) ###-#### ***** into left and right sides. Left side seems to have the colors consistent with 03 and 06 ECM colors. Right side has different colors but it doesn't matter because the circuit no is matching. I think ECM is color blind :)Are you sure whatever internal parts that "drives" the VSS and park/neutral switch are identical?
Expert:  Randall replied 1 year ago.

I am not and would prefer to opt out, Its just getting too complex from my end bouncing all these different specs, years and diagrams, I was answering based on information I do know but do not want to say each and every little difference outside of what the correct trans should be, You seem to have as much of the information on your end as I, I am sorry I can not help so will opt out and open the post to the other experts, One should be along soon to continue helping,

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