1997 Ford Contour engine warning light

DANOLEN

MEMBER
1997 FORD CONTOUR
6 CYL
FWD
AUTOMATIC
82,000 MILES

My daughter's car has an engine warning light on. We took it to an Auto Zone store to put on their diagnostic check and a code registered which was P0420 with the following explanation

OEM Brand: Domestic

Definition
Catalyst efficiency low-bank 1

Explanation
the oxygen sensors monitor the catalytic convertors ability to store oxygen

Probable causes
1. Catalytic converter defective (Failure possibly due to #2, 3 or 4)
2. Engine misfire or running condition
3. Large Vacuum leak
4. Engine oil leakage into echaust-valve guide seals, piston rings

Overall the car seems to run fine but occasionally when coming to a stop light or sign, the vehicle will idle rough or stall.

Occasionally there is a keening noise coming from the engine compartment, if I shift to neutral and blip the accelerator, the noise goes away.

I notice a heat smell when I open the hood to check for noise of any obvious leaks.

This is my daughters car that she drives at college. In 12 months, the car will be replaced when she graduates. I want to keep the car running without problems for the next year but don't want to spend thousands on repairs to make the warniong light go away.

Where do you start without replacing part after part to see if that fixes the problem?

2 Replies

SERVICE WRITER

MECHANIC
9,123 POSTS

In almost every instance that I have seen that code, the result has been a bad converter. If there was a misfire, other codes would be set as well as the vacuum leak would do the same. The heat smell is presume is coming from the converter as is is probably overheating from some restriction.

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Thursday, December 13th, 2007 AT 10:03 AM

RASMATAZ

MECHANIC
75,992 POSTS

Worst case scenario: you replace the converter with a new one, drive the car and Check Engine light comes back on. The P0420 code has returned. Now what? This kind of situation can be prevented by doing some additional diagnostics and research BEFORE your replace the converter.

To minimize this risk, it's a good idea to check the operation of the O2 sensors with a scan tool or scanner software. You should see normal switching activity in both sensors shortly after the engine is started, with the O2 sensor voltage switching back and forth between rich (over 0.8 volts) and lean (less than 0.3 volts). A flat line O2 sensor reading or one that shows little switching activity is a bad sign. The downstream O2 sensor should slow down and go flat when the converter lights off (if the catalyst is working). If it keeps on switching like the upstream sensor, it tells you the catalyst is probably bad and the converter needs to be replaced.

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Thursday, December 13th, 2007 AT 10:50 AM