I was told by the dealer I have a hard code stored for a knock sensor problem. I have no CEL. They would gladly charge me $600+ to change it. I wonder if the full of it? Any ideas?

My car seems to been running fine. 24mi gal hwy, 20mi gal city

 

run away as fast as you can

 

I don't know how the G is, so take this for what it's worth.
On most VQ's a failed/failing Knock Sensor stores a hidden code. Not all scanners will see it. This is referred to as a 'ghost code' by some people.

I've never heard it called a hard code. dunno what that means but perhaps they're eluding to the above.

Either way, you can buy a knock sensor and install it yourself, not that hard. Under $100.

A bad Knock sensor will set a default timing/fuel Map. This will rob some power and fuel economy. Kind of like a very very light limp mode. Most (all) drivers will never know they've lost the power/mileage unless the sensor is really bad, and even then, most will only notice the bad mileage.

The location of hte Knock sensors is a very high heat high vibration area, the housing is prone to cracking.
You CAN test the Knock sensor for ground and continuity, but that's about it, you can't really check it's active functionality. I'd recommend doing those 1st two tests, but you might not get conclusive results.

http://www.nicoclub.com/FSM/G35/Sedan/2004/ec.pdf

If both pass you're left with pulling it out to inspect the housing for damage. they're normally cracked. But it's hard enough to get out, that you won't want to put the old one back in, especially if it IS cracked. I recommend getting a new one.


AS FAR AS THE DEALER GOES: They can print out this fault. Request that. If they don't, they might be taking you for a ride.