My Nissan Frontier 2002 just turned off while I was driving. OBD II codes said P0300 then changed to P0302. Had the knock sensor changed, new spark plugs and new cables. Still turning off! Help!

...yes but the MAIN ground connection off the battery to the frame/chassis/fender was not tended to...undo the bolt and use a coarse wirebrush to restore the 300 or so cold cranking amps that this starter needs, yet can approach the needs of the ignition, fuel pump and accessories such as the windshield wipers, stereo and dash components reliably with steady voltage that doesn't waver in available amperage or voltages~

P3000 and P0302 are ignition misfires, which I believe will go away once proper grounding to the chassis, the ECU will have un-corrupted data to deal with~....could buy a cheap diagnostic scanner and "clear codes" with it~

http://www.obd-codes.com/p0300 --- check out the possible solutions section of this link. It might help you out.

...okay there is an "ignition relay" or "starter relay" you might look for this one~ https://www.google.com/#q=nissan+frontier+2002+ignition+relay&tbm=shop

Ground is good, no Check engine light.... Frontier still turns off while running

Could be low fuel pressure, try changing the fuel filter.

Changed the fuel filter and pump, broke and fixed a gas line in the process. Turned it on....it turned off. Checked the new spark plug cables and checked the ignition coil while my brother turned the switch and it turned on....and stayed on for a while. So went and got a new one and installed it... It worked! Rode the truck for 45 minutes straight! But then, the "repaired" gas line bursted and had to get towed home. Thanks guys!

One may ask...how pray tell did the gas line break?...you must have been OFF- roadin' it~

Oh no, it broke while he was changing the fuel pump and filter. He made a "quick fix" and it didn't work.

what? cross-threaded a connector and wasn't keen on aligning it properly?

migration_judge_roy is an ass.