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2004 Trailblazer, 6 cyl. 4X4 switch not lighting up. My GF took her truck to a transmission joint. They diagnosed the C0-327 error code and informed her her (EM) Encoder Motor was blown. They installed a new one, reset the system, and was thrown the very same code. After looking into it a bit further, they discovered that the encoder motor was being fed two additional volts, and explained to me (I was there during the repair process) that it was this over-voltage that was keeping the EM from working, thus the 4X4 inoperable. The T Shop went on the say that it was most likely this overage in volts that burned it out.

I will add at this point that the EM had been replaced about one year ago.

A reputable contact within a local Chevy dealership was somewhat beside himself that the C0-327 had been interpreted as a potential faulty EM. After I told him about the voltage issue, he mentioned something about a clutch pack, and further added that encoder motors are notoriously hardy; that they can really take punishment and that there is a snowballs chance that a constant push of two additional volts could burn it out.

I looked through the forum prior to posting, but was unable to find anything that covered the error code C0-327 combined with the extra-two-volts situation. She has cared for, and maintained her truck to the letter, and is the original owner.

And oh yah; I thought it amusing that you'd potentially be faced with flashing the 4X4 module...

LIST OF ITEMS HACKED...
-IPhone
-Razor
-PSP
-XBOX
-Nextar GPS
-IPod
-... TRUCK...

Hack a f*#-ing truck... who'd have thought! :laugh:
 

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I'm beside myself as well. The transmission joint robbed her. Did they offer no refund/discount for their incompetent diagnosis and wasted attempt at a repair?

I would predict it's a short between the motor drive wires and the encoder sensor reference or 5V input. Ten minutes MAX work with a meter and the schematic could distinguish the root cause. If it's not in the wiring harness, it's a fault inside the sensor/motor assembly (except that's been swapped multiple times) or the TCCM. Given the history, if I didn't see an obvious problem with the harness I'd get a junkard or Ebay TCCM.

If you reset the system by pulling underhood fuse #8 for 30 seconds, and put it back, does the TCCM wake up next time you turn the ignition to RUN, and illuminate the 2HI indicator lamp?

Does anybody have a meter and know how to use it if I pointed out some things to look at on the schematic?
 

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Discussion Starter #3 (Edited)
I have plenty of time to research, and most likely could grab access to a meter. We're in the process of swapping out parts with the TShop now. And yes; needless to say, there has been a 'stop payment' issued on check number 420 :cool:

Btw... :woot: ... you rock. Throw me what ya got....

(I'll pull the fuse once her old EM is re-installed. The shop recommended that the EM remain installed, but disconnected... again with that voltage issue. ID10Ts...)
 

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And get this; the transmission shop reported the EM receiving 4.9-something volts. I was just told by the Chevy Dealer's service manager of 11 years that the EM is supposed to receive 5 volts... :nono:.
 

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I agree. 5V is correct for the sensor reference. It's bloody instantly obvious from the schematic. What are they smoking?!?!?!?! I'm an electronics engineer, specializing in field failure analysis. And an offroader who might have to fix (and has) a broken 4WD system when 50 miles from pavement.

Anyway, the TCCM (run a search and find a picture I've posted before about its location above the driver's left knee) OR the encoder motor is the place you need to start probing.

The sensor is a potentiometer - a volume control - and gets a 5V reference (accurate) on one end, ground on the other end, and the signal on pin B varies from 0 to 5V according to where the rotation of the motor is in its travel. All this does is report back to the TCCM the motor's position, so the control module can confirm that when it tells the motor to move, it succeeds.

If the motor fails to move because a wire is disconnected, or the motor failed, or if it's jammed by mechanical damage inside the transfer case, such as the clutches, the TCCM will report that to the PCM, which will turn on the "Service 4WD" light. And the lights on the mode control switch (2HI, A4WD, 4HI, and 4LO) will go dark, signifying the TCCM is giving up.

The motor control wires D and E will be 12V on one, ground on the other, or vice versa (the schematic is not precise) depending on whether the motor has been commanded to rotate CW or CCW.

The "brake control" is just a safety interlock to make sure that a single failure of the motor control part of the TCCM can't command the TC to go into 4LO when you're driving along at 80 MPH. That would be a bad surprise, and ruin your day. :eek:
 

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Massive amounts of gratitude! :tiphat: I will definitely be looking these over, and grabbing a meter from a friend. It seems like this is a fairly common issue, so I'll post updates as they occur. The GF is also talking about having Chevy run a $98 diag in the next day or two. That mentioned, updates as they are available.

Thanks again :D
 

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Please help!!!

I have limited knowledge of 4wd systems but am mechanical I recently bought a 2004 trailblazer when I bought it I could switch to 4wd when at a stand still and it would click then I'd drive and it would ratchet I have discovered that the previous owner had two different sized tires on the front end if the vehicle and since the service 4wd light has come on and the 2hi light is on but no matter where you move the switch nothing occurs if I clear the code and then move the switch it will flash on whatever position then default back to 2hi. I have replaced the tired to correct size and was going to by an actuator but am not entirely sure that's what I need. Any insight or tips to prevent spending a ton of money for no reason would be much appreciated.
Thanks, Justin
 

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Please help!!!

I have limited knowledge of 4wd systems but am mechanical I recently bought a 2004 trailblazer when I bought it I could switch to 4wd when at a stand still and it would click then I'd drive and it would ratchet I have discovered that the previous owner had two different sized tires on the front end if the vehicle and since the service 4wd light has come on and the 2hi light is on but no matter where you move the switch nothing occurs if I clear the code and then move the switch it will flash on whatever position then default back to 2hi. I have replaced the tired to correct size and was going to by an actuator but am not entirely sure that's what I need. Any insight or tips to prevent spending a ton of money for no reason would be much appreciated.
Thanks, Justin
 

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JustinR4wf - I know this is a super zombie - but I just have to ask you a question, providing of course that you are still alive and still have this problem.

QUESTION; Are you shifting into 4WD while sitting still in NEUTRAL?

If you are in Drive, the change cannot completely happen and --- YES you will hear a ratcheting noise as the system tries to comply with your incorrect wishes.

Like I said - if you're still alive and can read this .................. just sayin' .........
 

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JustinR4wf - I know this is a super zombie - but I just have to ask you a question, providing of course that you are still alive and still have this problem.

QUESTION; Are you shifting into 4WD while sitting still in NEUTRAL?

If you are in Drive, the change cannot completely happen and --- YES you will hear a ratcheting noise as the system tries to comply with your incorrect wishes.

Like I said - if you're still alive and can read this .................. just sayin' .........

Actually, with these trucks you can do shifts to and from 2Hi, A4WD, and 4Hi at any time, moving or not, in drive or not. The only restricted shifts are 4Lo and nuetral.
Screenshot_20201030-225100.png
Screenshot_20201030-225109.png
Screenshot_20201030-225119.png
 

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That's nice to know. I have In/Out hubs on my K5 and I can go into 2H or 4H any time I want to too as long as I have the hubs locked. .

Like the K5 - I guess a TB won't be able to get into a reduction gear in motion.
 

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Good stuff --- thanks!
I copied and printed it for my own info.
Without ever having disassembled a transfer case it took me a long time and a lot of studying the imagery to get a grasp of how that all works. I still would like to see a teardown of that specific transfer case with good photo documentation.
 

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This TC isn't any different except for the clutch pack to allow a third almost-differential process inside the TC to keep driveshafts from winding up like wet noodles.

Most TCs can be repaired and rebuilt without even taking them out of the vehicle. Just pull off the tailcase and have at it.

I have a set of straight cut gears in my K5 - and I THINK I have another set that might fit my TB version too. When the weather breaks in Spring, I'm going into the TC for a look-see.

Besides - I've got to overhaul the front differential anyway. It leaks.
 
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