No 4X4 lights...

I have a 1999 Blazer that the 4X4 does not work. It does not light any of the indicator lights at any time and that includes the 2WD light. It's been like this since I bought the vehicle about a year or so ago.

I got an idea off the net the other day that it could be corrosion on the terminals on the tccm. I checked mine and found that the power wire on one the plugs was badly corroded but after cleaning and replugging back in, no change. I'd like to test the switch and the tccm to find out what I need to buy. Any help would be much appreciated.

I should mention that I bought this from an old couple that said 4X4 worked great until they laid it up (year or so of sitting because of stripped sunshell in transmission, they had just installed a brand new engine and couldn't afford to deal with transmission) so I figure that corrosion could be a likely culprit.

I have a 1999 Blazer that the 4X4 does not work. It does not light any of the indicator lights at any time and that includes the 2WD light. It's been like this since I bought the vehicle about a year or so ago.

I got an idea off the net the other day that it could be corrosion on the terminals on the tccm. I checked mine and found that the power wire on one the plugs was badly corroded but after cleaning and replugging back in, no change. I'd like to test the switch and the tccm to find out what I need to buy. Any help would be much appreciated.

I should mention that I bought this from an old couple that said 4X4 worked great until they laid it up (year or so of sitting because of stripped sunshell in transmission, they had just installed a brand new engine and couldn't afford to deal with transmission) so I figure that corrosion could be a likely culprit.


What transfer case?
Have you checked the fuses to it for 12 volt power both sides?

What transfer case?
Have you checked the fuses to it for 12 volt power both sides?

I'm not sure of transfer case model, it has 2Hi, 4Hi, 4Lo and Auto 4wd. Do you mean test for voltage by using the plug that goes to the tccm? What do you mean both sides? Could I just use a test light grounded to body or should use a voltage meter? Thanks for your reply...

Check the fuse or fuses to it for power on both sides of fuse key on.

Test light or volt meter will do that.
Then pull switch and check for 12 volts power to it and good ground.

If fuses are good and power to switch and ground you will need a transfer case scanner to get transfer case codes and to test it out.
If any codes post back codes.

There is two fuses for it.
One is the ATC fuse in underhood box.
The other one is 4WD fuse in IP panel box.

Be sure to test both.

Let us know what you find there.

Check the fuse or fuses to it for power on both sides of fuse key on.

Test light or volt meter will do that.
Then pull switch and check for 12 volts power to it and good ground.

If fuses are good and power to switch and ground you will need a transfer case scanner to get transfer case codes and to test it out.
If any codes post back codes.

There is two fuses for it.
One is the ATC fuse in underhood box.
The other one is 4WD fuse in IP panel box.

Be sure to test both.

Let us know what you find there.


I found ATC fuse missing(peculiar I'd say), put one in and checked, still nothing. With key on and fuse out I get power on one side (normal I guess) in both fuse locations. I found power at the switch and power at the tccm although not on the red wire, only on the orange. When wiggling the plugs/wires on the tccm, it flickers the indicator lights (sometimes just 4lo but sometimes all lights but Auto 4wd). I can't tell which wire triggers it or if it is the tccm not grounding properly. I tried holding a connection from tccm to body but didn't seem to do it. First time I've seen lights though, is there such thing as resetting it now. I have 4x4 fuse (inside vehicle) out and will leave it out for a while to see.

On another note, when I remove the 4x4 fuse inside vehicle, it makes sound at fuel pump and at something under hood (on engine, center rear approx...) but vehicle will run without it.

Thanks for your time...

Red is not a power feed to tccm.
ATC fuse powers the orange wire to TCCM.

The 4WD fuse powers the push button switch on brown wire.

Make sure both have power key on.
And alsp power on the switch and TCCM terminal that the wires go to plus check for good ground.
If plug in or wire wiggle makes thing come and go you have a problem there.

Also some switches have bad solder joints.

Red is not a power feed to tccm.
ATC fuse powers the orange wire to TCCM.

The 4WD fuse powers the push button switch on brown wire.

Make sure both have power key on.
And alsp power on the switch and TCCM terminal that the wires go to plus check for good ground.
If plug in or wire wiggle makes thing come and go you have a problem there.

Also some switches have bad solder joints.

It is now dark here so will try more tomorrow. I'll go over the wires better than I did earlier, they don't look broken but they probably are somehow at fault. Do you think I would need to reset anything such as what I read earlier...
disconnect the battery and let it sit for a 1/2 hour or so -- then reconnect the battery and cycle the ignition from on to off three times -- this should reset the TCCM.

I haven't tried this yet but will try...

Disconnecting the battery does not help much on OBD11 stuff.
Pulling the TCCM fuse should reset it.
Give it a try.
Let us know how it goes.