type of lube for diff

I have a 99' GMC Sierra z71, reg. cab. What type of lube do you use for the diff. ? Also, how can you clear the message center when it shows service 4x4, check engine , etc. Just got this truck and these seem to be some of the lil things that I can see wrong. I also have that ticking when cranked and it goes away when the truck is ran a while. I saw the post about the heater but mine doesnt have that plug. Any ideas?

Kinardracing

My book says to run 75w90 synthetic, you may also need to run limited slip additive.

Thanks for the response. Any suggestions on my other problems? lol

per tech bulletin:
All 8.6 axles OK with synthetic
All 9.5 axles mid Feb 98 & up OK with synthetic
Pre mid Feb 98 - no synthetic unless RTV sealer
used is replaced with gasket upgrade. the synthetic
will eat the RTV

I'm not sure about the Service 4x4 but the check engine light means you have something wrong and the computer has stored a code. You need to have the codes read with a OBDII scanner and clear them. Look up the codes in a service manual to find what the problem is. It could be something as simple as a wire unplugged.

James

To clear the message service 4X4 and ses, like stated above you will have to get an obd2 scanner and find out what the problem is first, then you will have to fix the problem. You can try to clear the codes and see if they come back. As far as the service 4x4 light it will either be the pos push button switch or the accuator on the front diff. both comon problems.

Before replacing parts, you might want to look at this info I found:

Q: I've got a '96 GMC Jimmy, I didn't use the 4WD much over the last year and when I tried to engage the 4WD, the HI light first flashed then did nothing so I tried the LOW and it did the same. It is now showing no response at all when pushing on either button and does not engage in 4WD. Any ideas on what I should have a mechanic look for to fix?

A: The most common problem we see with these systems is an encoder failure. This means the computer module that controls and monitors the 4WD shifting motor doesn't know where it is. The computer needs to know the location of the shifting motor to perform correctly. If the computer loses location information it stops responding. Diagnostic codes can be extracted but, because you have not used your 4WD much it may be all that you have to do is to clear the computer so it can start over. Turn the ignition switch off and remove the fuse marked T-case (it should be a 20 amp fuse). Wait a minimum of 3 minutes then replace the fuse. Once the fuse is replaced turn the ignition switch on & off 5 times. Then start the engine and push the 4 Wheel HI button. If the system starts working, great. Be sure to exercise the 4WD system regularly to prevent a reoccurrence. If the problem returns then you need a technician familiar with your 4WD system to get into some diagnosis.