My wife's 2000 Maxima has had its share of problems. At 40K, a seized rear caliper, now at 44K its been throwing the "service engine soon light." Recently it started flashing. The dealership says it needs all new ignition coils, and they cannot get a code on which one is misfiring. I take it to a non-nissan garage, and they get little or no information on each diagnostic. I think back to when the car was 2 or 3 years old and recall that it had issues with knocking, (with no trouble lights) and the dealer poo-pooed it as bad gas or low octane fuel. I think this is a Nissan bungle that they won't own up to. I am baffled, I've never had such issues with any car previous. Any suggestions??? Anyone?[:@]

 

The coils are a common problem, they go bad quite frequently, and most people have to replace usually up to 4, but occasionally they do require all 6 coils to be replaced.
if the knocking went away, I don't think they are related, even if the knock did not go away, I don't see how a knock could cause coils to go bad.

 

My 1999 SE had the same issue. At first I was like you...unsure as to which coil was bad. I ended up buying a ODB scanner myself and clearing the codes until it actually showed me which one was failing. Overall, it took almost 2 weeks for the ECU to indicate which ones were failing. Eventually, the ECU will tell you, but at first you will get a "Multiple Misfire"... Don't despair...

I ended up replacing all of them out of frustration, it tunred out that three were bad, so I wanted to get that issue overwith. Replacing all six as well as my O2 sensor brought my Maxima back to it's potential.

If you are looking to replace them, Rock Auto, or Redline Maxima has a good deal on them...should run you about 50 - 60 per.

You may want to replace your plugs too. Make sure that you go with the NGK iridiums, Bosch is crap! Denso also makes a good plug.

If you aren't willing to buy an ODB scanner, you can go to any Advance or Autozone to have them scan and clear your codes for FREE!

I hope this helps...

Judas