Renewed complete exhaust system from manifold back on my 1998 mercury mountaineer. Now there is a P0420 code coming up. Anyone have any ideas ? Thanks


Asked by Nov 21, 2015 at 11:21 AM about the 1998 Mercury Mountaineer 4 Dr STD AWD SUV

Question type: Maintenance & Repair

Had all catalytic converters, sensors and pipes replaced by mechanic. Had a misfire code but took care of that. Now have a P0420 cade (catalytic converter efficiency below standard bank 1) . Mechanic is now talking about injectors. Any ideas would be gratefully appreciated.

4 Answers

Tom Demyan

Could be many things, sorry you have a mechanic who is just guessing.... Replacing the whole exhaust for big $$$$ to find out that isn't the issue is hard to swallow

Best Answer

Thanks Tom. The exhaust system needed to be replaced anyway and it was better to do it now than in the middle of winter. The "check engine " light does not come on when there is a P0420 code and it sometimes runs a little rough when stopped at the lights. Do you think it could be an injector leak ? Thanks.

Tom Demyan

It's on the list of possibilities, but without diagnosing your car, I'd be guessing. Try another mechanic to get a second opinion.


Hi Tom, I have had a couple of other mechanics diagnose the problem and most only use a simple OBD II code reader which of course gives the same results as I get. One charged $87 and had the car for a day to get the same result so I'm a little skeptical of their ability. I am thinking I will try testing the injectors next and move onto the vacuum hoses after that. Thanks for your time, I appreciate it.

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