I have a CEL on my truck that comes on few a couple minutes, then goes off for a few minutes and continues.

I scanned her today and got three codes, 335, 336, and 337.

335 = EGR sensor circuit voltage higher or lower then expected.
336 = EGR sensor circuit voltage higher then expected.
337 = EGR sensor circuit above maximum voltage.

any ideas what i could look for and where?

i'm clueless.........

1994 3.0 4x4

 

I am going to start here even if this thread is as old as Jesus and has no replies... so my 94 2.3l Mazda B2300 has started to throw up codes again. The CEL has been intermittent lately then started staying on just yesterday. The whole time I have religiously been doing the KOEO test every time I turn the engine off...so what i noticed was that the codes 335, 336, and 337 came up in that order over a period of 3 days ... so I assume my voltage is rising... right? But I am clueless as to why. RON if you see this HELP!

 

You should start your own thread, always, people hardly look at 13 year old threads, lol

335 (O) EGR feedback signal is/was out of range - EVR or PFE
336 (O,R,M) PFE sensor signal is/was was high - ">PFE
337 (O,R,M) EGR feedback signal is/was was high - EVR

So EGR system issue
In this case EGR sensor issue that's what "feedback" means
I think 1994 2.3l used a DPFE type sensor, 2 hoses 3 wires
Check the hoses for cracks, they are port specific, so don't mix them up
The hoses can get moisture inside(exhaust gases) so make sure they are clean
Check 3 wire connector for corrosion
Put everything back together and see if codes come back
If so replace DPFE, common failure when they get older(years and years), the moisture in the system eventually kills them