I own a 99 2500 diesel auto trans. First the check engine light came on and off no on all the time and now have been having a problem with the Tach Gauge. It will not work sometimes mostly when first starting, but will work and then not work, noticed the trans not shifting correctly when not working. Also noticed a rough idle when not working. Please help me if you can.

Thank you, Scott

 

The very first thing to check is your grounds. The battery to frame, battery to body, and battery to engine grounds should all be redone with real bolt-on battery straps and the mounting points cleaned free of paint and rust and coated with dielectric grease.

 

Its probably your crankshaft position sensor (very common). It will make the trans. shift bad (auto) and make the tach very irradict.
If you pop your hood and look down at the harmonic balancer, you will see a black piece of metal that is right above and off to the left with a wire loom attached to it that goes up. It probably needs adjusted. You can do this by loosening the bolt and use a matchbook cover to set the space. Or the wires have contacted the harmonic balancer and started to rub through or have rubbed through. Check the harness carefully, I mean pull the sensor and take the wireloom off and look. If they have rubbed through, cut them and solder (not solderless connectors) them back together. A new one is about $75.
Let us know if this was it.

 

Thanks for your input I will look into it this weekend, been working very late every night, I work at the US Capitol and the house and senate have been fighting over our tax money all week. I took a look under the hood trying to find the crank sensor and nothing near the balancer but I have a haynes manual and they say it is back by the oil dipstick pipe on the engine block, I took a look earlier and it is going to be hard to get to, may have to take out the plastic piece in the wheel well then I may be able to see it.

 

Maybe on the 99s they moved it.

 

It is actually behind the starter. I've had them come out easy, and have had a few that I had break off! I then used a dent puller type slide hammer with a drywall screw to get it to come out. What A PAIN! But usually not a big deal.

 

yes its behind the starter. its a pain have to pull the starter.mine did the same thing. put a new one on and problem fixed.