Hi there,

just found this forum site - can't explain why I haven't come across it before having owned my Blazer since 2002!

It's a '99 UK Export RHD build and it's still not topped 50K miles yet.

Any way on to the crux of my problem.
Summary: drive stuck in 2HI and won't shift to either 4HI or Auto

I've scanned a number of the threads about 4WD problems but due to lack of experience with 4WD auto transmissions, I've got to where I think I need some pointers.

I have the 4 button dash-mounted electronic transfer case control switch part nbr 15709327 (AKA 19168767) which I thought had gone kaput so just had a replacement shipped out, but when fitted it did not fix the problem like it did back in 2007. thought it worth trying the easy option first.
So now it's back to square one.

Symptom Details:
engine idling, vehicle stationery in Park/Neutral/Drive/Reverse, when I press either 4HI or Auto the LED on the respective button flashes, there is the faintest click somewhere, the idling engine speed drops by about 100-200 revs for 5 seconds then returns to normal, but the LED stays blinking and the slected drive does not engage. Eventually the system reverts to 2HI by itself. Regardless of the position of the auto box floor mounted drive selector (P/N/D/R) including shifting between them, the 4WD cannot be engaged.

Hope I've given enough details, but holler if I have not.
I've just spent a small fortune having the BCM replaced to fix the starting problem that gradually escalated from being inconvenient to outright breakdown WNS requiring recovery to the garage to get it sorted.
Now I still can't use the Chevy because we've got real snow here in the UK and it won't engage 4WD!

Any assistance anyone can give will be greatly appreciated.

 

Pull the passenger side kick panel and have a look at the electrical connections to the TCCM (at least that is where it is located on the LHD models... Not sure where it is for RHD if that is what you have). It is very common for there to be corrosion problems in this connector that can inhibit shifting.

 

Thanks for the quick response Swartlkk, how can I easily identify the TCCM (Transfer Case Control Module?) - will it have a readily visible sticker with a part or code on it I can look for? The BCM is in the same place on both Left & Right hookers, so chances are this unit will be in the same location also, BUT Sod's Law generally kick's in at this point. ;-)

 

Take a look at the NV236 wiring thread in the Tech Article (DIY) Index link found in my signature. It will have the connector views which should help you identify the TCCM.

 

OK I located the unit behind the passenger kick panel mounted on a metal plate with 3 bolts, two connectors: C2 small black 4 contact supplying power and C1 large 32 pin orange where there looked to be some corrosion deposits on one or more of the pins, so I attempted to clean that and the surrounding pins with a small file - also did the power contacts at same time. Re-assembled unit and tested, but still no successful shift into Auto, 4Hi, or Neutral (forgot to mention that previously).
There's still a click from the TCCM immediately when I select Auto or 4Hi from 2Hi, but the LED on the selected button just blinks away. There's also a click from the TCCM when I reselect 2Hi, but it is delayed by about 5 seconds.
Is there anything else I should have done to the TCCM?
If not, what's the next thing to look at or test?

 

Are you confident that you did not enlarge the terminals during the cleaning process to where they would not make proper contact with the pins in the TCCM?

Is your 'service 4wd' light on in the dash? If it is, get the TCCM scanned for codes.

 

I only cleaned the pins on the TCCM I did not tinker with the connector. I don't think I have a file small enough to insert into one of the pin holes. I was hoping that by cleaning the pins the action of re-connecting it would clean the contact in the connector. Maybe I need to disconnect/re-connect a few more times?
No the 4WD service light is not illuminated on the dashboard.

 

Small brass pipe cleaners work great for cleaning the terminals in the connector.

 

OK, thanks.
I guess I need to visit a pipe smoker's retail outlet then to find them. The only ones I recall my late father-in-law using were the standard white cotton-covered wires.
I'll report back in due course...

 

Hi SWARTLKK,

latest update:

I have cleaned up the connector terminals and pins again using a hobbyist mini diamond finished hand file set so I am pretty certain that all the contacts are now making a circuit.

Having finished that and re-tested I am still unable to successfully engage 4WD, but have managed to engage Neutral, and when I then select 4Hi the rear axle clunks when re-engaging.

There is still no clunk from the front axle, and makes no difference what option the auto box selector is in, the selected option (4Hi or Auto) button LED just continues to flash away and eventually revert to 2Hi.

Accordingly is it fair to say that the TCCM is now operating satisfactorily, and attention needs to shift to the front axle actuator that actually engages the drive to the front wheels? Or is there something else I need to check first?