Hello,
I have a 2005 Sonata 4cyld Automatic plain Jane,bone stock. Going to work this morning tach drops to zero,check engine light comes on and temp guage starts going up. Car ran fine after this and I ended up turning on the heater to bring temp. needle down a bit. After a few miles tach needle starts working again but check engine light still on and temp is still up. I havent pulled any codes just yet. I thought I would toss this out there and see what you guys thought or see if anyone else ever ran into this? Someone told me it could be a alternator issue. Lights didn't dim and car starts right up so I find that kind of weird. Someone else said crank sensor going bad? Any ideas from you guys?

 

It might be an electrical problem like a short somewhere or a bad ground. Definitely get the codes scanned though. I'm assuming this is a case where the instruments started acting funny but the car is still running fine? You say the tach dropped to zero but the engine stayed running right? The temp gauge may have been giving the wrong reading due to an electrical fault. I've heard of that before.

 

Rally,
Thanks for the reply. After pulling the code and doing some research I seem to have solved the problem. Pulled code and it said the Ignition Failure Sensor was bad. Replaced it and tach works good and no check engine light on. Car still showed that it was getting hot. Replaced battery ground to engine and did a thermostat and now all is well. Don't really know if it was just one thing or all three but between the three I seem to have no more issues... Atleast for now...