My big block 2005 Avalanche has been great, but for quite a while, now I cannot get the 4wd to engage.
I have NORMAL lights on the dash switch no blinking, no service 4wd light in the cluster and 2wd is fine
If I push either 4wd button, I hear the system trying to engage the front axle it will CLUNK 5-6 times with the chosen 4wd button flashing, then revert to the 2wd light position........No engagement........
I thought that since there is response , but no engagement the switch must be good, and the round actuator that screws into the front axle was bad, like the travel on the 'plunger' was not enough.
I bought one and installed it in 15 minutes................Yep, the reason I am here is to tell you that was not the problem.
I have the same clunking but no engagement problem.......
Right now nowhere close to where I live to get a scanner check.
Let me know your thoughts on this , this website seems very good
Last edited by goodride (4/3/2016 6:19 PM)
There have been problems with the speed sensors for the front and rear drive shafts. Check the connectors for proper installment making sure the plugs don't slip out of the connector. If it does then there is a service bulletin on replacing the plug and or wire harness.
The speed sensor signal may have become corrupted. Possible openings in the speed sensor wire insulation (twisted pairs) can allow water intrusion. Also wire connections contaminated by water may result in short circuits and erroneous speed sensor readings. This most often occurs on the rear speed sensor circuit.
To help repair this problem according to the service bulletin number Bulletin No.: 05-04-21-003C Date: April 15, 2008 Subject: Service 4WD Light Illuminated, DTC C0374 Set (Inspect Wiring Harness to Transfer Case speed sensors).
Replace or repair wiring harness use service connector pack, P/N 88987993 at the speed sensor end and terminal, P/N 15326267 if needed.
Also check the control module for water intrusion, corrosion or loose connectors.
It would be better is you could get a scanner on the truck to get any trouble codes that may be stored in the system. I know you said it is hard to get to one but sometimes a local auto parts store will scan your truck for free. Check it out if you can, knowing the trouble code is a big help if you can get it.
Get back to me with your results when you can. We can diagnose the problem further if needed.
Thanks for your quick reply.
I thought since I hear the 4wd TRY TO ENGAGE of course not at speed, at idle in neutral....
the process to get 4wd has started, but there is a mechanical reason preventing the engagement....
..yeah gonna get the scan next.