Contour Enthusiasts Group Archives Forums General Troubleshooting CEL codes PO430 and PO174

'97 Contour Sport, 6-cylinder, 5-speed, 122,500 miles

Situation: The CEL light comes on, bring it to AutoZone and find out these two wonderful sets of digits: PO430 and PO174. It's not the first time that these codes have appeared. Over the years I think I've replaced the O2 sensors at least a half-dozen times. Most recently my cat convertor was replaced and I can't understand why this would be happening again. For someone who's always taken care of his vehicles, I have never encountered SO MANY problems with this one. I guess there's always bound to be one bad one in the bunch.

Question: Is there some inheren't problem with the O2 sensors in the Contours? Seems like it's a pretty commonplace situation.

Happy Holidays to All!

I would hazard a guess that the two are related.

Going from lean to rich can trigger a false CAT code.
Look for a problem on the front bank - more than likely a bad intake manifold gasket. Such a leak will cause a lean condition on that bank and cause more fuel to be dumped. This will cause a subsequent rich condition, and some of the extra fuel burning in the pre-cat will then cause the CAT code.

I think you just need to change the O2 sensor. On my 99 I got a P0420 and the code for the O2 sensor failing to switch causing lean condition, I forget the number, I suppose it is P0173. We replaced the sensor and the Cat code has not come back at all, not yet anyway

p0174 and p0430 are not related. expect to find a vacuum leak or low fuel pressure causing the p0174. It may not be just on bank 2 also - there could be a "pending" code p0171 that aftermarket scanners aren't capable of reading. As for the p0430, they do not indicate a sensor problem. p0420 and p0430 are set by comparing the switch ratio between the front and rear sensors. When the rear switch rate reaches 75% of the front switch rate on two consecutive drive cycles teh light is set. Which catalytic convertor was replaced?