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Ford Taurus | Mercury Sable | Ford Taurus SHO | 1986-2007 Forum for discussion of the Ford Taurus, Mercury Sable and Ford Taurus SHO. Covers vehicle years: 1986-2007

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Old 09-19-2007, 06:32   #1 (permalink)
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dtc p0420

having a small problem with a mil. need to know where to start. have a dtc p0420 i listened for a vacuum leak and hear nothing. i dont have a lift at the time so im not able to lift the car but if i have to i will. i just need a starting point or even just tell me where to go and i'll be grateful.
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Old 09-19-2007, 13:44   #2 (permalink)
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Re: dtc p0420

That is the O2 sensor after the cat saying the cat isn't doing it's job. Either the cat is bad or the O2 sensor on Bank 1, the exhaust pipe coming from the firewall side of the engine.
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Old 01-10-2008, 06:39   #3 (permalink)
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Re: dtc p0420

ok.... i know that it has taken me awhile to reply, but i have been very busy. I replaced the first O2 sensor after the cat and the same code is showing up. I also banged on the cat with a hammer and heard no ratter so my conclusion is that the cat is good. Any oher ideas because im clueless.
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Old 01-10-2008, 09:32   #4 (permalink)
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Re: dtc p0420

It would be helpful to know what year and engine you have.
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Old 01-10-2008, 10:09   #5 (permalink)
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Re: dtc p0420

Diagnostic Trouble Codes (DTC) P0420 and P0421 indicate that bank 1 catalyst system efficiency is below the acceptable threshold.

NOTE 1: Complete the spark timing check in Quick Test before proceeding with this test step. Spark timing retarded below specification can increase exhaust gas temperature and decrease catalyst efficiency over time.

NOTE 2: Be sure customer has not:

Refueled vehicle with leaded gasoline.
Noticed high vehicle oil consumption.

NOTE 3: If entering this Pinpoint Test for symptoms only, go immediately to HF5 .

NOTE 4: Internal deterioration of a catalytic converter is usually caused by abnormal engine operation upstream of the catalyst. Events that can produce higher than normal temperatures in the catalyst are particularly suspect. For example, misfiring can cause higher than normal catalyst operating temperatures.

Possible causes:

Use of leaded fuel.
Oil contamination.
Cylinder misfiring.
Damaged HO2S.
Damaged ECT sensor.
Downstream HO2S wires improperly connected.
Fuel pressure too high.
Damaged exhaust system pipe.
Damaged exhaust manifold.
Damaged muffler/tailpipe assembly.
Damaged catalytic converter.
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Old 01-10-2008, 20:04   #6 (permalink)
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Re: dtc p0420

P0420 = Bad Cat!
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