Hi all, As the title says, I have a couple questions on my 1999 Blazer push button 4wd.No lights are on and the service 4wd light is. Here is what I have done: I removed the 10A fuse and the service light goes out, the fuel gauge goes to empty, and the shift indicator light goes off. Still no 4wd lights. I'll drive it like this a short bit, and turn hard to see if I feel it in 4wd. Doesn't seem to be. I then turn the engine off, put the fuse back in, and sometimes the 2hi light comes on, sometimes the service light comes on with no 4wd lights. When the 2hi light comes on, I can push the 4hi and 4lo buttons and everything works fine. However, I turn the key off, and back on, the service light will come on 75% of the time, the 2hi light the other 25%. Pull fuse, repeat, and repeat again. I got it to show 2hi, and then jacked up each front wheel and spun them freely, driveshaft stayed put. But the front driveshaft will not turn by hand in park or nuetral. I do hear a whining noise when driving. So my question is this, even though the light will show 2hi, would it still really be in 4wd, and what would be the next step in troubleshooting? Oh, and I've pulled the vacuum lines from the actuator under the battery tray and no difference was made. I've read here that the front driveshaft should spin freely, but mine doesn't seem to want to. I also read about codes from the 4wd lights, but no explanation to what 1, 2, 3, or 4 mean. Thanks.

 

Need some more information. Do you have Auto4wd? If not, then see the article in the DIY section, OBD2 Non-Automatic Transfer Case Diagnostics. It has the DTC1-4 explanations.

Many of these problems have been covered in past posts. A few searches and some reading and I am sure that you would find information that will allow you to repair your truck.

One of the most common problems with these 4wd systems is due to corrosion at the electrical connections to the TCCM (transfer case control module) which is located behind the passenger kick panel.

 

Yes, it has auto4wd as one of the buttons. I've read most thread links at the bottom and I guess they have me a bit confused. maybe too much info all at once, lol.

 

The auto4wd option complicates things. You cannot access the stored TCCM codes by the easy method. You must use a Tech2 or equivalent high feature scan tool to communicate with the TCCM directly.

Check the electrical connections at the TCCM first. Next, I would check that the vacuum actuator is getting engine vacuum if/when you activate 4HI.

There should be a vacuum switch that is mounted to the firewall near the distributor. This switch allows vacuum to go to the front axle and is used for the Auto4wd mode. If this switch has failed closed, it may cause the system to malfunction.

If there is no engine vacuum at the electronic switch on the firewall, the next thing to check would be the vacuum switch on the transfer case.

 

vacuum from lower hose (comes from tees at driverside) at firewall switch: yes. Vacuum to upper hosegoing to battery tray actuator: no. I assume then the switch is stuck closed preventing any vacuum to continue past this switch? This is all while the dash light fails to go on. And the service light is on.

 

Again, start with the connections at the TCCM. If they are good, you really should get the TCCM codes read. A good repair shop should have the proper scanner to access the TCCM. If you cannot find one, then you will need to go to a dealer. It can get quite expensive if you just try replacing components. The "Service 4wd" light is trying to tell you something.

 

Thanks, I will see if the local shop has a reader. Looks like it'll cost money either way, lol.

 

True, but at least you won't be wasting time and money just taking the shotgun approach to replacing parts.

 

Well, I brought it in, and the first diagnosis was the encoder motor, but after more testing they said it was a short in the wire to transfer case motor. That's as far as they got. Armed with that, is there a way to start checking for shorts? continuity light starting at the TCCM? any ideas welcome.