Contour Enthusiasts Group Archives Forums General Troubleshooting P0420 Catalyst System Efficiency below Limit

P0420 Catalyst System Efficiency below Limit - Bank No 1.

Just got my code checked and this was it, I was told it is an Oxygen sensor...didn't know if this was covered under my extended warranty or not?? also if not how much of a pain this sensor is to get at? thanks

This is usually not an oxygen sensor problem. This is usually a marginal or dead cat. Your emissions warranty may cover it. Your extended warranty probably does not.

Your car has four oxygen sensors. One on each bank before any cats, and one after the front cat on each bank. The oxygen sensor behind the cat is actually called a cat monitor. It tells how effeciently the cat is operating.

An oxygen sensor produces a small voltage in the presence of oxygen. 0 voltage is a lean reading. .9 volts is a rich reading. The oxygen sensor is constantly switching between 0 and .9 on a properly running engine. The cat tends to stabilize the oxygen sensor readings so the swing between rich and lean will be either much slower or nearly non existant from the cat monitor oxygen sensor if the cat is working properly. The PCM compares the front and rear oxygen sensor and screams "tilt" if the readings are switching nearly at the same speed, turns on the check engine light, and sets a code. The cat monitor system in the PCM does not run constantly. It is an intermittant test that is only done when certain conditions are met including that all other monitors have run and the the engine is well warmed up.

On California emission system cars, the cats are warranted for 7/70. On Federal emission system cars, the cats are warranted for 8/80.

With all that said, I have had that code set on my car from time to time and the cat seems to have restored itself. I have not had it on for at least a year. I have scanned the oxygen sensors and the cat monitor oxygen sensors and they are switching as expected, fast in front and very slow in rear. The cat has not been replaced. It may help that I clean the throttle body, intake manifold, combustion chambers, and injectors often and keep the ignition system and air filter is exception condition.

Let us know how things work out with this.

contours and mustangs have the same problems..in that removing parts to get better performance will cause codes
to pop up and you may have to use MIL eliminators to
turn off the chek engine light.

I had this code intermittently as a result of a faulty
DPFE sensor. (I believe).
I'm not 100% sure how they are connected, I was having EGR
related and P0420 codes, and replacing the sensor fixed it.

Tiv

Thanks all for the suggestions, I read some back posts and saw how many people had faulty cats and this was triggering the error code, however stealerships insist that you change the o2 sensors first.... I will take it in for service after I get back from my honeymoon since I have no time before and I will try and get them to stipulate that if changing the o2s does not remedy the problem that they will reimburse the cost...with all going on now I really cannot afford to play guess that error with the car and I would love to have it be a cat which is covered under the 8/80K...I am in MA so I think that I should be ok with that regard....also any info on exactly what my extended warranty does cover would be appreciated, thanks

My 96 SE at 76,??? miles got its first CEL, the same 420. Took it to the dealer, they replaced both pre-cats under the extended emissions warranty, no questions asked. These are my second set, the first were replaced at 33,000 miles at the time of the original recall. Take it to a different dealer if they give you problems. Just know you might be without your car for a few days.

I have seen on multiple cars that it was just the 02 sensor. When the O2 was replaced the code went away and never returned. I think the dealerships are wasting there time and money when they replace the precats.

I've had that same code for some time now, but I just haven't had a chance to troubleshoot it. Before buying any new parts, I'm going to try swapping the O2 sensors from the front to rear bank. If the sensor's at fault, then I'd expect the code should change.

Also, I've heard you can clean an O2 sensor tip with a propane torch? Not to hijack this thread, but does anyone have information on that?