General Question

I have to admit that this is not about the Chrysler, but this is one of the
better newsgroups for information. So I hope nobody minds that I ask.

We are considering buying a car that has the "check engine" light on.
Anticipating that this might be the case when I went to look at it, I
brought the handy code scanner with me.

The scanner said o420. The code description is "Catalyst System Efficiency
Below Threshold (Bank 1). What I have been able to determine, so far is that
either:

1. The downstream O2 sensor is misreading the output of the catalytic
converter or
2. The catalytic converter isn't doing it's job properly, which the O2
sensor is correctly reporting.

The car is a 2000 Mazda Protégé with about 115K miles on it. Thanks in
advance.

Ken

 

I wouldn't mind if you cross-posted this to rec.autos.makers.mazda but since
you didn't it's like your saying that the Mazda owners on Usenet are a bunch
of morons.

If the owner doesen't have receipts for an o2 sensor replacement I'd
assume at minimum that BOTH components have had it.

Replace all o2 sensors in the vehicle and make doubly damn sure there
are no holes in the exhaust system, then feed the car highway miles for
about 5K miles, and with a big slice of luck you might not have to replace
the converter.

Ted

 

They are simply not as supportive. Thanks for your input, Ted.

Ken

 

I hope you read the rest of my post regarding the o2 sensors.

Ted

 

I did. Thanks again, Ted.