OK - thanks for the info ... will keep chasing the HVAC deal.. but trying to determine why the "Service 4WD" light comes on every day in about the same stretch of road - flat, straight, just cruising about 50mph - when I drive to work.

 

Any TCCM codes stored? If you are looking for this vacuum switch, you obviously have a 4-button TC.

 

I haven't been able to get to anyone with an advanced scan tool. Tried the shorting out pins on connector and looked for code flashes found in the "4x4 No Worky" thread - but none showed .. not sure if that was actually written for Blazers since I didn't see any sign of a contact on pin 13 of my connector.

And yes - 4 button - 2000 Blazer LT with just over 250K.

 

Yeah, the 4-button won't flash out the codes by jumpering - requires a scanner or software that will do the manufacturer's-specific communication with the TCCM. Not sure what software or scanners other than the Tech 2 can do this on the Blazers, but has been a subject of interest to me.

When i had problems I was able to communicate with my TCCM using a OBD2 terminal on a laptop and a OBDLinkSX (USB) OBD2 adapter by typing in the raw computer heiroglyphics and reading the ones sent back by the car, in order to read and clear codes. It works but you have to be a bit tech savvy to pull it off. Another person got me going by providing what heiroglypics to send and what they mean. If you are interested in doing this yourself, we can discuss further.

What I do know is that the Tech2 has a lot of functions/monitors used with the factory diagnosis charts that makes 4WD diagnosis a breeze. If you don't have the Tech2, you still end up having to make some educated guesses and/or developing your own way of diagnosing with a multimeter (once you understand exactly how the system works and what area the problem lies). Still it helps to know what code (if any) is being set. Then you know what area to look in at least.

The one quick easy thing to check on these systems is for corrosion on the TCCM connectors. If you find corrosion, clean things up, apply dielectric grease, and see if your problem goes away.

Also easy to check is the control switch, as it just requires an ohmmeter (specific resistances on a specific circuit should be observed when pushing buttons).

Often more difficult to diagnose without the Tech2 are the TCCM and the Encoder motor. Unfortunately they are the expensive parts and one going out can damage the other. My encoder motor shorted out intermittently and was blowing fuses - eventually this took out the TCCM too as current for the Encoder motor goes through the TCCM. Had to replace both to get 4WD working at all. This front axle staying locked in was the last piece of my 4WD problems (only caused poor mileage and resistance to rolling when turning wheels sharply while backing out of my driveway at very slow speed). I am happy to report that my milkeage seems to be up a couple of MPG since the last repair.

I recently obtained some new software for my Android that may have some canned TCCM communication possibilities for reading/clearing TCCM codes (as well as many other systems). Exactly what it will do and will not do on the Blazers I am slowly evaluating. I do know the program has a GM 4WD module, and it connects to the proper address when I select it (1A in heiroglyphics). But since I don't currently have any codes I don't know if it will read/clear them or not.

Problem is that the car manufacturers can require different communication, depending on the vehicle and year and system type - with the manufacturer-specific stuff like 4WD there is no standard - so what works for one make/year/model of vehicle may or may not work for another. The software I am looking at recently is Car Gauge Pro (about $8) and the adapter is BAFX Bluetooth from Amazon (about $25). I do know that the GM ABS module provided in the software will not connect at all with the Blazer, so it's a try and see for all the different modules at this point. All I have done so far is to make a list of what modules it appears to connect to on my particular vehicles. I have also bought the $90 OBDLinkMX adapter and found no funtional difference to the $25 BAFX on my vehicles. That probably is not the case for some newer vehicles, since as the OBDLinkMX is not Elm327. Conversely, the software will connect to and do a lot with the ABS on my 2008 Ford Ranger, but that vehicle uses CAN protocol communication (more modern). See what I am getting at? I imagine some of the more pricey softwares with their own specific hardware interfaces cover a lot more vehicles consistently.

Good luck and let us know if we can help!

 

Thanks for the helpful info Les. I have removed the connector from the TCCM and didn't see any evident corrosion. And I am fairly tech savvy - hex code can indeed seem like hieroglyphics. What do you use with the OBDLinkSX to talk like an Egyptian? I saw one on Amazon last week but it required a "Pro" upgrade to read GM FWD codes that was nearly $200 IIRC.

EDIT - checking out bluetooth adapters - wow they're cheap.

 

I used ScanXLPro (GM enhanced) on a Laptop but that was just because I already had the software and I knew it had a terminal mode that another person had successfuly used with the OBDLinkSX on a Blazer.

As I understand it the OBDLinkSX comes with a program suitable for doing the required terminal mode but I have never yet installed it. When you have the hex code and the hardware right for communication in Egyptian, the simple software you use to type/display hex code doesn't matter

What I have never heard of is a person doing this with a bluetooth adapter and an Android terminal. Not sure if USB adapters are subject to Elm327 protocols like the bluetooth ones. However I suspect it is possible and I have downloaded the Elm327 terminal by the same guy that makes Car Gauge Pro for Android ($8 - which by the way will display CMP retard for our Blazers). I intended to try the terminal mode through my bluetooth adapter with Scan XL Pro first (BAFX Bluetooth OBD2 adapter sold on Amazon is by far the best cheap one - check out the reviews on Amazon) but I have not yet done so. It's all pretty interesting stuff, but not a priority once your 4WD works right!

But I can say that if ScanXLPro can indeed communicate "Egyptian" through a bluetooth (and remember I have not done that yet to prove it), then an Android certainly should be able to do the same with some sort of terminal software. What type of adapter you buy depends on how much you want to do with it later. I have 2 USB OBD2 hardwires (one proprietary for HP Tuners, and the generic OBDLinkSX I bought for SCan XLPro. I have 2 Elm 327 devices. One Wifi adapter I tried to use with my iPhone (it was very poor) and the BAFX bluetooth adapter I use with Torque Pro and Car Gauge Pro on my Android. I find the laptop and hardwire interface cumbersome, and the software expensive - but these are definitely superior in both speed and what you can do with them. But common things the Bluetooth and Torque Pro or now Car Gauge Pro is my favorite. Heck I leave the adapter plugged in an forget about it. Then at any given moment I can whip out my phone and be monitoring stuff. But if I want to do a crank relearn or injector balance testing or control my TCC or transmission, etc, I have to hook up the laptop and use HPTuners. Honestly, Scan XLPro is the only software that I don't really need anymore as HP Tuners covers all that it does and more (at a price) and Car Gauge Pro will display the CMP retard (shy I originally bought it) through bluetooth.

If you want to try do this, all the info I have on the hex code is in post 4 of this thread.

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

the saga for repairing my 4WD encoder and TCCM is here:

https://blazerforum.com/forum/2nd-ge...or-lock-89046/

Please read these and if any questions feel free to ask.

Good luck,

Les

 

I found info somewhere on the web (forget where - been looking soooo much) that indicates it may be merely a dash switch issue. The forum article said the TCCM monitors the switch voltage/resistance and if it doesn't receive proper feedback within 5 minutes it throws an error. Seemed like the "Service 4WD" happens about 5 minutes every time so tonight drove it and bang - 5 minutes into two trips the light came on. Sooo - gonna get one and replace it and see if that fixes it... fingers crossed.

 

Just an update on the solution *hopefully* (I hate searching for similar problems and never seeing what solution was found).

Well got a new dash switch and the light still came on after 5 mins - regular as clockwork. So went to a junkyard and got one off a '99 with similar numbers on the case (not sure what all those numbers mean) and the correct connectors. Cleaned it up and stuck it in and sooooo far it has passed the five minute test. So tomorrow will drive it and see how it does.

Other weirdness was this morning - before I got the new (used) TCCM - after driving a while and getting off the interstate ... left a stop sign, cruising about 45 and the 4WD Low light started flashing while 2WD HI was engaged and still lit - for about 30 seconds - and I was praying that the switch that won't let the TC engage at speed kept working - and it did and all was well. Also three times over the weekend when starting from a parking spot it started in 4WD Low - and I had to sit in neutral and switch to Auto - then 2 HI to get going again. So does that sound like a wacky TCCM?