No idea whats causing these error codes

hello we have a 1996 that has error codes p0300 and p0138. the light has been on for awhile and we dont know what causing it any help is appreciated!

oh sorry i guess i typed to fast its a 1996 dodge neon. sorry!

I don’t see a P0300. P1300 indicates a random misfire. P0301 indicates misfire in cylinder #1, P0302 indicates a misfire in cylinder #2, etc.

P0138 is secondary oxygen sensor circuit high voltage.

Hope that helps.

what could cause the random misfires? the ignition coil wires and plugs are all new?

here are sites that i found. and

I noticed that “faulty oxygen sensor” is listed as a possible cause of a random misfire. Perhaps the O2 sensor is causing both codes. I’d have someone test the O2 sensor and see if it needs to be replaced.

A fuel system problem can also cause misfires. How old is the fuel filter?

Actually, P0300 is the code that indicates a random multi-cylinder misfire. P0138 has something to do with an oxygen sensor.

With a 1996 Neon, you have to consider the possibility that the codes don’t mean anything at all. Our 1995 turned on the Check Engine light several times a year for no valid reason. My experience was that it was best to clear the code(s) and see if they returned before taking them seriously. There is a fuse in the fuse box under the hood that you can remove momentarily to clear the codes – memory says it’s the Radio fuse, but it could be something else.

That said, Oxygen sensors don’t last forever and it’s entirely possible that it actually needs replacing. An aftermarket sensor from Autozone or the like should be fine.

Here’s a link on P0300 –

um until now we did not know it had one. we thought it wasnt suppose to have one. but were glad u mentioned it were gonna look and see if it does and if so more than likely its shot