The tach in my 2006 1500 stopped working. I've read a lot of treads on this issue and performed the tests from the service manual. All gauges sweep appropriately except the tach (doesn't move at all), and there are no diagnostic codes.

I'm fairly certain that the cluster is toast. However, at the end of the test it appears that there are codes showing on the Odometer-I 285, C 447, and S 127. I cannot find any reference to these codes and they are not mentioned in the manual with the test.

Any one know what these mean or where to find a reference to them?

 

I haven't tried this yet, but I plan to this week

 

My 06 mega reads low as well. I am going to do this fix sometime this week, I already need to replace some bulbs, so I might as well kill 2 birds with one stone. I'll post my results when I'm done.

 

Careful. The cluster is a computer in and of itself that I believe is called the cabin control module. A hot iron and plastic printed circuits have many possible bad outcomes. I think I remember reading here that someone tried this fix only to find that it was temporary.

Good luck. I still need to know what those codes mean, if anything.

 

Yeah, I was kind of thinking that too. I'd hate to screw it up to try and save a tach that really isn't all that necessary anyway. I'm in no position to be shelling out $800 for a new cluster. The tach works, it's just at idle it tends to drop a little. Nothing like the OP's problem.
Think I'll just replace the burnt out bulbs and call it a day.

 

Just pulled my cluster out today, was hoping to replace the bad bulb. I'm going to have to order them from Rock Auto. No big deal to remove the cluster again. I decided after looking at the back of the cluster not to touch it with a soldering iron. Way too much room for error. I pulled the black cover off the back, and the damn thing looked like a computer. No way I'm going to mess with that.

 

I performed this today. I had a little trouble removing the radio bezel, but all in all went fairly smooth.

I used the soldering iron as the video shows (I haven't soldered in over 10 years). Reinstalled everything with ease.

My tach is now working as it should.

 

I was able to get the bulbs from my local dealer, reinstalled cluster, and, for now, my tach is working fine. I chalk it up to the cluster being jostled around, and nothing more.

 

This makes me wonder if a "remove and reinstall" may fix this. I didn't really feel like I did much with the iron.

 

Interesting. Taking the cluster out is no big deal. I checked the price of a new cluster with the local dealer and was told $200-300. Maybe it's $800 if they do the work. That's a lot of money for an unnecessary item. Someone here called them "stealerships", a moniker with which I do not necessarily disagree.