I have three engine code on, two for two O2 sensors and one for EGR Value ($350). My mechanic is suspecting a short somewhere. My O2 sensors give almost 0 home resistance when it should give about 6 ohms. My question is this, repair is going to cost me quite a bit esp that the car is running 100% OK, it is just the checkengine light on, that I need to take care of.

  1. Is there an easy and standard way to find short in the circuit? My car did give me some indication of it. If I dont drive it for a day or two, it might not start because of almost dead battery.

  2. Can if fix the EGR value which is kind of expensive?

The car is MAZDA 626 year 2000

this page lists side affects of bad EGR value, my car has none of these. No rough idling (800 rpm idle), great fuel economy, no knocking, no overheating.

2 Answers 2


The only foreseeable problem would come from mixture problems due to your O2 sensor readings. Look for a wiring diagram somewhere, and see if the components share any common grounds or points. Repairing a wire can be cheap if you can do it, as the bulk of the labor cost will likely come in trouble shooting it. As far as the EGR goes, it is more of an emissions item and unless leaking would likely not cause any bad problems. It recirculates unburnt gas from your exhaust to decrease the amount released into the atmosphere.


I assume youre talking about a parasitic drain. A "short" is easy to find because it will blow a fuse. Take a compass around the wiring and it will point to the location of a "short". Another easy way to find a short is using a guass gage(google it)

  • 1
    there was a parasitic drain problem before but now i confirmed, started the car after 2 weeks and it started quick. So I assume that was just the battery problem (which I replaced). How can Use compass to detect fuse?
    – TheTechGuy
    Nov 20, 2011 at 14:05

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