Blazer 4wd works ONLY in Auto 4wd

HI

I'm dealing with a 2000 S- Blazer in which 4WD will ONLY work in "Auto 4wd". No codes have been set.

Initial problem was intermittent 4wd engagement and also once the vehicle disengaged while in 4wd into neutral. The Service 4wd light has come on only once and as stated NO service codes.

I have already changed the switch after finding loose soder joints. After replacing this there you can hear the TCCM and vacuum exhausting etc as you switch from 2 --> 4 etc ( which is an improvement ) BUT the 4wd is not actually engaging EXCEPT in Auto 4wd. I have also rebooted the system.

ANY ideas?? where to go next??

Thanks

Welcome to AF.
How are you checking for 4W engagement?
Any service engine or transmission or transfer case lights coming on?
Will the transfer case shift from high to low range?
Is the front axel locking in in 4H and 4Low range?
Does the 4W shift lights all come on for a bulb check key on and the go off?

Hi and thanks for repling.

How are you checking for 4W engagement? --- All 4 wheels have power to them - and it will pull out of the snow, 4H or 4L will not - rear wheels spin only
Any service engine or transmission or transfer case lights coming on? --- ONLY the one time "Service 4wd"
Will the transfer case shift from high to low range? -- All I hear when going 4H or 4L is the tccm click - but nothing @ the encoder motor or power to front wheels.
Is the front axel locking in in 4H and 4Low range? -- NO , only when Auto 4wd is selected
Does the 4W shift lights all come on for a bulb check key on and the go off? _--- yes__They also come on when 4H or 4L are selected - before changing the switch they would flash and then go back to 2wd position.

Thanks____________

You will need to get it hooked up to a transmission/transfer case/engine capable scanner.
A lot of info and shifting test and code reading and transfer case data with a transfer case scanner.
It should point you to the prbblem.
Get codes and post back code no.
And we can help.
Mt

Thanks -

Not to sound stupid but. . .is there a separate scanner for the transfer case? I have the OBDII scanner and it shows me NO DTC's. ALthough I haven't driven with it and looked at the streaming info.

You need a high end high dollar scanner manf spefic engine and transmission transfer case capable scanner.
The OBD11 scanners will not rear or check transfer case computter stuff.
And AZ scanners does not do it either.