Hey Les
Having played with my friends 2000 blazer today with NP8 , I'm 99% sure that your TCCM IS at $1A and if you use the code 6C 1A F1 19 C2 FF 00
you will get your DTC just like your post read up ......and 6C 1A F1 14 will clear your code when your ready..... 2000-02 and 03 are all at $1A ....I'll bet most GM's are

 

Houston, we have TCCM Communication!

With the connector off the TCCM I checked the encoder motor wires for short to ground with an ohmmeter - was fine. Put another fuse in and did the 6C 1A F1 19 C2 FF 00 (current codes) in OBDII Terminal of Scan XL Pro. Got a 6C F1 1A 59 00 00 93 BB back (00 00 indicates no current codes). 4WD selector switch lights appeared normal showing 2WD lit steady. No Service 4WD message. I then did the 6C 1A F1 14 (code clear) to see what it would do. It made the TCCM click loudly and the TCCM gave back a 6C F1 1A 54 8E. Need to determine what the 8E stands for - hope it means codes were successfully cleared. Unfortunately when I went to start it up and take it for a drive to try to induce a problem, I found the battery had run down. So it's on the charger. I'm done for tonight!

If anyone can tell what the 8E coming back after clearing codes means, that would truly give me a warm and fuzzy feeling.

Got it started and all seemed fine. Selected Auto and control light lit and stayed lit (not slick enough close to my house to try it out). Then selected 4WDHi. Flashed for a bit and then went back to auto. Then selected 4WD LO while rolling in neutral. All button lights went out and service 4WD came on. Checked fuse and voltage to TCCM - still good.

Checked current codes and got back a 6C F1 1A 59 43 87 93 67 which translates to a CO387 Transfer Case Shift Failure.

Per Captain's link provided in post#8, the encoder motor either can't get where it wants to go or it can't recognize when it gets there. Factory diagnosic charts appear to have the problem being either a problem with wiring between the TCCM and the encoder motor, or the encoder motor assembly (which could include position sensors and unlock) is bad. Unfortunately I don't know the hexadecimal commands to do the acutal factory diagnostic chart with the OBD terminal. But I can check/inspec all the wiring from TCCM to encoder motor for continuity and no shorts to ground. If all that is OK - then it must be encoder motor, and with a couple blown fuses in the recent past this seems likely. It does seem the TCCM is OK.

At least that's my logic at the moment. What do you guys think?

Les

 

I'm going to go with encoder as well, I seen a broken wire once and the code was permanent , when the encoder was bad the code would only show up with the light on.....weird.

 

So I put a brand new encoder motor on this weekend. Definitely made a difference but still not operational. Removed the old one and turned the transfer case through its range with a wrench until I felt a springy stop at each end of the range. Took maybe 10ft lbs max to click the case through its range. Does this sound about right? Could tell when in neutral as could turn the rear driveshaft. That is the position the encoder motor came in. Now I can hear the motor running when I push a button (was absolutely quiet right before replacement). Unfortunately it ultimately goes to flashing 4WDHi and stays there (for at least a couple of minutes) without setting a code or turning on the 4WD light.

For example if I press 2WDHi I can hear the motor run for a few seconds - shut off - then start up again for about the same time and goes back to flashing 4WDHi. Seems motor can't get where it wants to go (or can't recognize when it's there) and then it returns to its point of origin? (this is definitely a question I would like to have answered!)

So I checked the voltage on the 4 encoder signal circuits at TCCM pins E5-E8 and found the voltage on E6 (Encoder circuit C), and E7 (Encoder circuit B) were both pulled down to ground (indicating two positions at the same time?). Can't seem to find which circuit gets pulled down at what transfer case position - help please. If I disconnect the 6-wire connector at the encoder motor, all 4 of these circuits show 5V as they should. I then disconnected the TCCM and checked resistance between E6 and E7 - there was no continuity between them. The encoder motor lock circuit is being completed by the TCCM as measured with a voltmeter at the TCCM as it begins to operate. Note all of this is shown on the 4th schematic down on this post:

https://blazerforum.com/forum/2nd-ge...-blazer-89044/

So it seems like I still don't know Whether the TCCM is internally screwed up and is pulling down the voltage on a second encoder circuit when the encoder moder pulls the first one down - or if it is possible for two Hall effect encoder motor sensors to be tripped at the same time by the motor position being in between them. This is my biggest question. It does not seem to me like it would be possible for two Hall effect sensors to trip at the same time. In that case the TCCM would have to be bad. Yes, I know it would be easy to figure out with the Tech 2 scanner, but I don't have one and I'm not going to pay someone I'm not sure about to try to diagnose it without my standing right there.

I did check for codes with the 6 wire connector off the encoder motor to verify it is capable of recognizing a malfunction and setting a code - yet when I plug the connector back in, clear codes, and try to select 2WDHI it will return to a flashing 4WDHi indefinitely without setting a code and the service 4WD light does not come on.

So what do you think?

p.s. if the transfer case has actually gone bad, with all the other problems in this vehicle returning or starting to return (false misfire code, oil pressure, knocks when hot), I'll button this POS up and trade it off at whatever loss I have to take to be rid of it. My requirement for any further work is that the 4WD works on my 4WD vehicle. Otherwise it is worthless to me and I draw the line on putting a transfer case in it in addition to fixing the engine again. I kind of wonder if the two problems are related since they were both fine and the engine went downhill fast again less than 2 weeks after the first 4WD problem appeared and even blew fuses for some time, but I can't figure out how unless the encoder motor was shorting to the transfer case and ended up running juice through the crank bearings while searching for a ground. If this is the case, running the juice through the transfer case might have screwed it up as well. I did check for the outside of transfer case being grounded well when selecting 4WD with a volt meter before removing the encoder motor, but at that time it was no longer blowing ATC fuses (guess the encoder motor had completely shelled electronically by that time).

Thanks for listening and for any help you can give. I find if I can write things out in a post it also helps me think and put things into perspective.

Les

 

Lots & lots of information to absorb here. Check post #10 again


Gotta do it before you try to shift it after installation.

 

Thanks Captain! Yep I previously understood your message about clearing the codes. It's also why I later intentionally set a code, read it, and then verified I could actually clear it using the obd2 terminal method and my laptop. Wanted to make sure the code clearing was actually happening. Probably I'm going to go ahead with the TCCM but I have a bad feeling that the TC shifting may be sticky. Unfortunately I have no frame of reference to judge correct shifting effort for a known good transfer case. Any info you can help with will be greatly appreciated.

 

The new encoder is shipped in the neutral position. The case must be manually shifted to the neutral position to install the encoder. When everything is mounted and connected, that's when the DTC's need to be cleared, BEFORE you try to shift it with the switch. Is that how you did it?

 

Yes, manually shifted to neutral with the encoder off - then installed encoder in neutral position. Turned key on and cleared codes with my laptop rig. Then tried to select 2WDHi and encoder motor ran 2x for several seconds each with a slight pause between. At that point the 4WDHi button was flashing. Push 2WDHi again and same sequence with motor running happened again - ending up with 4WD flashing again and no service 4WD light on and no codes set. I can say that the transfer case did move out of neutral as I can no longer turn the back wheels.

Is this typical operation when codes are not cleared with a tech2? Could it be that clearing codes with my laptop does not do the same thing as a tech 2? Or could it be indicative of a problem where the encoder motor cannot physically complete the shift. Or is there something wrong with the TCCM where it can't read the position of the encoder motor correctly (2 circuits pulled down to ground at the same time). Trying to understand what the system is trying to do when I push the 2WDHi button.

Thanks for any enlightenment you can give.

Les

 

I'm firmly convinced the encoder motor was definitely bad, since it stopped blowing ATC fuses and I can acutally now hear it running. Still it will not complete the shift for whatever reason. I have checked out all the wiring between the TCCM and encoder motor with a meter and it is all good and not shorted. I have verified that I can click the Transfer Case selector between the different positions using a wrench - so that is presumably OK (unless it is simply too stiff for the motor to handle). I have installed the encoder motor in the neutral position and cleared codes using my laptop and the OBD2 Terminal code method before trying to operate the new encoder motor. I have subsequently verified that I can create a fault - then display a code and clear the code using the OBD2 terminal mode method. Encoder signal curcuits B and C are both being pulled down to ground, presumably indicating that the encoder is either between positions or the TCCM is internally shorted, pulling down voltage on both circuits when only one circuit is tripped by the hall effect. Terminals for Encoder signals B and C are right beside each other on the TCCM board.

So I still don't know if my transfer case is screwed up and the new encoder motor can't get it where its suppose to go, or if the TCCM was also taken out by the bad encoder. I want the 4WD fixed before I spend any more effort or money on the engine. If it's the transfer case itself, I will probably trade the vehicle as is and I won't deal with the engine as it's not very bad yet.

I am really starting to believe that the encoder motor was shorting internally and running current to ground internally through the transfer case, transmission, and the thrust bearing - taking the thrust bearing out again, with subsequent additonal bearing wear. The engine was beautiful for 2 months after the 100% rebuild that was done. Then the 4WD started acting up, the torque converter stopped locking, and within 1-2 weeks almost all the engine symptoms appeared again (P0304, suddenly lower oil pressure, some bearing knock at RPM). I am betting they are all somehow related. What a cascade of problems/symptoms! It all could have potentially come from a bad encoder motor.

At this point I'm going to throw the cheaper part at it and see what happens (about the same price as a hook up the scanner at the dealer). I was able to negotiate a really good price for the Cardone Rebuilt TCCM with Summit Racing, on a Beat the Price with Parts Geek. In addition to beating the total to the door by $1, they found they couldn't lower the core charge, so they ended up taking additional off the price of the merchandise. Heckuvadeal I think! Who knows if it will fix things but what's another $113 at this point. If it does fix it - then great - if it doesn't then I'll know it's transfer case. I really wish I could have gained an idea of how much torque it should take to move the transfer case selector with the wrench, but that is water under the bridge at this point. I still would be interested if anyone has a transfer case out and a way to measure the torque required.

AAZ-73-42102 BODY CONTROL COMPUTER
Shipping From Manufacturer $113.23 1 $113.23

Merchandise Total $113.23

Core Charge$114.00

Total Charges $227.23

 

The TCCM ultimately controls the encoder motor, not the BCM. All of the modules request and supply data to one another through the network. If the TCCM receives the proper data from each module, it will command the shift. During the shift, if the TCCM doesn't receive the expected data back from the encoder or axle engagement switch, the TCCM commands the encoder back to the original position.