Still Getting Engine Malfuntion Light

[foxylady23]

Hello again
I wrote back in August about the Engine Malfuntion Light coming on and off and got alot of opinions as to the cause.Had it tested at 3 different Auto Zones and got PO420 code from each test. Car has always run fine with light on or off and getting great mpg. Called Honda and tech said it could just be a sensor ands unless something starts happening, don't worry about it since mechanics cannot promise that changing catalytic converter will stop light from coming on, cuz it could be the sensor.
So 9 months later I still get the light on and off. Off more then on.Car runs fine.Whatcha think?
Also brake light was coming on for first 10 miles on cool mornings but will deal with that on anotherr thread.Just wanted t omake sure they are not related electrically. Thanks in advance.

[jeffcoslacker]

If the brake fluid level is just at the threshold for the sensor to trip the light, it'll do that, cold fluid will sit a little lower in the resevoir, once you drive a little and the fluid near the wheels warms up and pushes back a bit, the level in the resevoir comes up slightly and the light goes out.

I don't know what that code means on your car, what does it indicate? You might run fine, but fail a smog test, if that's done where you live. That's an OBDII code, so your car must be a '97 or newer, so if you go to get a smog test with a SES light on, it'll fail.

[Igovert500]

P0420 67 Catalyst System Efficiency below Threshold.


Don't know what year, but as Jeff said you will fail an inspection if you have those in your state. A bad cat usually smells bad (rotten eggs bad), causes excess soot out the tailpipe, perhaps some black smoke, maybe even random backfires.

As you said, it could also be a failing o2 sensor. If it completely failed, I would think it would throw it's own code though. So are you getting any of the above symptoms?

[jeffcoslacker]

Originally Posted by Igovert500

P0420 67 Catalyst System Efficiency below Threshold.


Don't know what year, but as Jeff said you will fail an inspection if you have those in your state. A bad cat usually smells bad (rotten eggs bad), causes excess soot out the tailpipe, perhaps some black smoke, maybe even random backfires.

As you said, it could also be a failing o2 sensor. If it completely failed, I would think it would throw it's own code though. So are you getting any of the above symptoms?

Sooting and performance problems usually only occur when the convertor is beginning to get blocked, when it's fully restricted it'll cause engine overheating, stalling, power loss and exhaust valve burning.

A simple test with a vacuum gauge can tell if it's blocked or not, but I doubt it or you'd be noticing it.

They'll code for o2 sensor if the ECM doesn't see enough variation in the readings (indicating a dead sensor), but the efficiency codes happen when there is little or no difference between the pre- and post-cat readings, so it assumes the cat is not functioning correctly. With the cross-checking between the two sensors, it's very unlikely that a sensor malfunction would throw a cat related code.

Chances are the cat really is bad. An exhaust shop can check the convertor's temp while running and tell if the catalyst is dying.