Instructions for reading codes (check engine)

[rick619]

I have a check engine light and my code reader is saying no codes found.

I had a check engine a few months ago and the code reader was able to read it then, cylinder misfire. Got that fixed under warranty.

So I've tried with the engine power in all 3 positions, engine off and engine on. It's still saying no codes found. Not sure what I'm doing wrong. I checked youtube and didn't find a good video showing the proper procedure.

 

[2025 Ram Limited]

I had mine come on on Monday while cruising down the highway. Everything seemed to work as normal and then yesterday morning it went off. Some think it could be signs of a battery going bad. I have had the truck for a year now and this was the first time.

 

[John Kloehr]

Some (most typical from auto parts stores) only read P codes, the light could be due to a code in a different system (B, C, or U codes). Also some will only read active, not pending, codes. But if the dash light is on, there is an active code.

Anyway, key in engine-on position should be fine for all cases.

 

[2025 Ram Limited]

Some (most typical from auto parts stores) only read P codes, the light could be due to a code in a different system (B, C, or U codes). Also some will only read active, not pending, codes. But if the dash light is on, there is an active code.

Anyway, key in engine-on position should be fine for all cases.

So when the light went off by itself that means it cleared the code on it's own? With all the electronics on these trucks it seems odd.

 

[LaxDfns15]

So when the light went off by itself that means it cleared the code on it's own? With all the electronics on these trucks it seems odd.

The event that caused the code could have gone away, but the code should still be stored in the system. It just won't be active.

 

[rick619]

Some (most typical from auto parts stores) only read P codes, the light could be due to a code in a different system (B, C, or U codes). Also some will only read active, not pending, codes. But if the dash light is on, there is an active code.

Anyway, key in engine-on position should be fine for all cases.

The check engine light was still there this morning. It is ready for an oil change, not sure if that would cause a check engine?

I tried the code reader again when I got to work. Still saying no codes found. Really odd.

Seemed to drive like normal on the way to work, so not likely a cylinder misfire again. I was likely going to an oil change place to have that done. Now probably just have it done at the dealer. It's a '23, but I bought it new in '24 almost exactly 2 years ago. So still under warranty at 15K miles.

 

[rick619]

I had mine come on on Monday while cruising down the highway. Everything seemed to work as normal and then yesterday morning it went off. Some think it could be signs of a battery going bad. I have had the truck for a year now and this was the first time.

I did have an issue with it not starting around a year ago. AAA said nothing wrong with the battery. The dealer couldn't find any problems and replaced the battery anyway. So hopefully not that (though and easy fix).

 

[rick619]

I'm bringing it to the dealer Saturday.