My check engine light is on


Asked by Feb 18, 2014 at 01:24 PM about the 1994 Dodge Ram 1500 2 Dr LT 4WD Standard Cab LB

Question type: Maintenance & Repair

My check engine light is on and the codes that flash are 12 and 21. the truck idles rough
and i replaced the iac sensor thinking that was the problem. didn't fix it, and haven't gotten
around to replacing the O2 sensor just yet, but I don't think that would cause it to sputter
and almost die, or would it?

11 Answers


O2 sensors will not cause any rough idle or misfire how do you know is code 20 and 21?

1 out of 1 people think this is helpful.

if you do the on off on off on deal with the ignition the check engine light flashes to give you the codes that are registered. it flashes once pauses then twice and pauses making it a 12, twice pause once pause making it a 21, and then it does the twice pause once again.


If you rev the engine does it backfire?


no it doesn't. it did it to me today and it almost died completely and the oil pressure light started to come on. i tapped the accelerator and it went back to normal.


You mean it back fired today?


no it has never backfired. what i meant is it was starting to sputter on me and almost died. sorry for the confusion


Do you have a distributor?


If I do it is not readily accessible. I can trace my plug wires to the back of the block, but i can't really tell what they are plugging in to.


What size engine do you have?


it's the 5.2L V8. I am thinking maybe the TPS but my multi meter has gone MIA....


Only be concerned with the code 21. The code 12 is just telling you that the battery has been recently disconnected. Code 21 is a problem with the oxygen sensor circuit. It's shorted. You'll have to inspect the wiring going to the oxygen sensor. HTH. -Jim

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