I have RPO NP1. Has anyone had a TCCM work intermittently? I mean sometimes I push the 4HI button and it shifts flawlessly and other times the button flashes and nothing, even though I can hear the TCCM click. Push it again and it shifts, sometimes. It also sometimes does not shift even into 4LO. It has shifted to 4LO with both 4LO and the 4HI buttons illuminated. Other times it will shift into 4LO with no indicator light in the button. I can clear the TCCM and get it to work again for a few shifts and then problems again. Also sometimes it shifts w/o lighting any of the buttons up to tell me what range it is in. I've switched TCCM's with the same end result. Granted it was a used TCCM but it tested fine when I bought it. Also I had times when no range lights light up when I start it. Most times when I start the truck all three buttons light up and then go out except the one, usually 2WD, stays on. I believe this is supposed to indicate the TCCM passed its self check. It's doing so many weird things it's hard to track them all. I really hate intermittent faults. I've tried grounding out pin 13 to pin 4 in the OBD connector to get any DTC's stored in the TCCM and got no lights at all on the 4x4 switch. The three fuses I know of for the 4x4 system are all good. I've checked the TCCM connections for corrosion, none found. I tried a brand new three button switch, nothing changed. I have a rebuilt Cardone TCCM coming but I'm wondering if it could be the position sensor in the encoder motor. Does the four wheel drive indicator switch on the front axle have anything to do with whether or not the TCCM will shift the transfer case? Is there another sensor I should look at? I can hear the front axle lock when it goes into four wheel drive but I hear nothing when it unlocks in 2WD.

 

I had similar issues issues at one time. Long story short, took the selector switch apart and found a hairline crack on one of the pin solder joints. Only could see it with a 10x loop. Reflowed the solder and added a bit also on all the pin solder joints. Fixed the problem. These was several years ago and I have since seen several Gen2 S/T series trucks that needed the same fix. So you might want to take a look at that.

EDIT: Here is the thread I did on it at the time https://blazerforum.com/forum/2nd-ge...tch-fix-96894/

 

Thanks for the reminder. I had reflowed the solder on another switch I had. It fixed the shifting but the bulb I wanted to fix was burned out and I fried the board trying to replace it. I just reflowed and added solder to the pins on my current switch. I noticed the 2WD button wasn't popping back up like the others. I opened the switch and checked the rubber boot, it was half torn by the metal conductor I replace the torn conductor w/ one from another switch hoping this was the cause of my problem but it was not.

 

Check the attached out, pay particular attention to how he describes the checks if you get no lights when you ground pin #13 (you should at least get one flash):

EDIT: Note: Not saying you need to jump to replacing TCCM if self test fails. Can do some additional circuit testing first, but might want to follow the steps listed when you don't get a flash after grounding pin 13:
"2. If the TCCM failed the Self-Test, then test the following circuits: a. Battery Positive Voltage (40 and 1640), and Ignition 3 Voltage for battery voltage. b. Ground Circuit for ground. c. Diagnostic enable circuit for an open or high resistance. d. Transfer case shift control switch connector."

 

That is a great help. My TCCM passes the self check. I tried grounding pin 13 to pin 4 again and it worked, I now wonder if I had not pushed my wire in deep enough. DTC2 "encoder motor does not function correctly enough times" was displayed. It got me thinking of the 4x4 switch again as I was having a similar problem last year. I decided to clear the DTC from the TCCM and reflow the solder on the switch pins again, adding a little solder this time. First time pushing 4HI it flashed but did not shift. Second push and it shifted into 4HI. I drove it forward and reverse for about fifty feet. Stopped and shifted it to 4LO. Shifted flawlessly so I drove it forwards until it shifted to second gear no problem and backed up fine. I just returned from a road test shifting from 2WD to 4HI and back again several times and it worked flawlessly. I don't want to jinx myself but it looks like I don't need to be looking for an encoder motor, at least not at the moment. I will be shopping for another 4x4 switch though. I tried a brand new one from Dorman and I'm not impressed.

 

Great news (knock on wood). Don't know if it needs to be pointed out or not, but when range shifting into 4LO, insure the trans is in "Neutral" (not "Park") for automatic transmission or with clutch pedal fully depressed for manual transmission. Speed has to be below 3 mph.

I've learned that non OE parts (especially Dorman) is a crap shoot. But sometimes there's no choice for new because a part has been discontinued. Sometimes I'll even go to pick-n-pull to get an OE part, even though it's used, depends on the part needed.

Ever since I reflowed the solder on the original switch, I've yet to see it fail. So I'm not even concerned about replacing it.

 

Thanks for the help and thank you for your service brother!