Contour Enthusiasts Group Archives Forums General Troubleshooting cel? p0420 catalyst efficiency below threshold......

whats this mean? is it the cat or the oxygen sensors? the EXACT message on the scanner is P0420 CATALYST EFFICIENCY BELOW THRESHOLD (BANK 1)
also whats bank 1?
thanx for the help
corey

Probably means your catalytic converter is about to die. Bank one refers to cylinder bank one I think.

i dont think thats it....i was just told BUT i want to be sure before i start replacing things, that the code is for an oxygen sensor, and bank 1 is the bank which includes plug #1
tell me if im correct

Bank one is the rear bank against the firewall. Try changing the rear lower O2 sensor and resetting the computer to see if it goes away, although the code suggest that the rear precat is f**ked. Time to buy some headers!

another question then, are the precats in the header, so if i were to buy the sho y pipe with hi flow cat it wouldnt make a difference as far as this is concerned

Corey, or anyone else.
How did you get the readout for the CEL? Did you have to go to a dealer? What did it cost?

i work at a gas station that has a garage, i just came in and borrowed the odb 2 scanner and used it.......i was actually thinkin about buying one for myself and keepin it in the car

Ack - I just got this error code too. Same exact thing, same bank. How did you resolve this? Was it a bad cat? Or just bad O2 sensor?

I'm really hoping its an O2 sensor. I had all three cats replaced under warranty at 40k, when they disintegrated and plugged up. I hope this doesn't mean one of the cats died again. It runs fine. I can deal with replacing an O2 sensor. I can't deal with replacing the precat and exhaust manifold on the rear cylinder bank.

Found this it does kinda look like the converter, since there is a code for bad or slow O2 sensor. A bigger question is what caused it. 2nd paragraph gives a few hints, but I believe it's a little out of date.
I'm still looking.

Any Ford Tech listening, what do they do?

On 1996 and newer vehicles with OBDII, the on-board diagnostics will usually catch a bad converter. The OBDII system monitors converter efficiency with a second oxygen sensor mounted behind the converter. The system compares oxygen levels ahead of and behind the converter to see if there's a difference.
Downstream oxygen levels should be lower if the converter is working properly. Little or no change in the downstream O2 readings means nothing is happening inside the converter.
This will usually cause the OBDII system to illuminate the malfunction indicator lamp (MIL) or the Check-Engine light and set a fault code. The generic OBDII code for low converter efficiency is P0420.

Replacement Diagnosis

Replacing the converter will restore proper emissions performance. But the new converter will suffer the same fate as the old one unless you figure out what caused the original problem. Look for fouled spark plugs or wires, low or no cylinder compression, or a computerized feedback system that stays in open loop all the time.
On a dual-cat system, the side with the bad converter tells you which cylinder bank to check. If the converter on the right is bad, for example, check the O2 sensor, spark plugs and compression on the right cylinder bank.
Always replace the oxygen sensor. Converters needs an air/fuel mixture that is constantly flip-flopping from rich to lean. If the sensor is sluggish or dead, the fuel feedback loop will flip-flop too slowly or remain rich all the time.
Bad coolant sensors will also keep the fuel system in open loop. A thermostat that's stuck open or is too cold for the application can also cause similar problems.
It's also important to check the air pump and related plumbing as these components provide fresh air for the converter to reburn the pollutants in the exhaust. If the air pump isn't working right, it can reduce the converter's operating efficiency significantly
Paul

A few months ago, my check engine light came on after a long freeway drive and about four miles off the freeway. I had it scanned and got the same results reported here. I also scanned the operation of the oxygen sensors and found that the rear sensor was switching frequently showing that the cat was not doing well. I cleared the code and drove the car for several weeks before the light came on again. I read the codes again and scanned the operation of the oxygen sensors and found the same problem, which is what I expected. The cat monitor system does not constantly check the cat operation. There is a certain sequence of driving that must take place before the cat monitor will look at those readings. So I expected that I would probably need to buy a rear pre cat before the next time the car needed to be smoged. I cleared the code again.

About two weeks ago the light came on again and I read the codes and found that the light was set by a loose gas cap. My daughter had filled the tank last and didn't get the cap on straight. Since I had the scanner hooked up, I took a look at the oxygen sensors and to my surprise I found them to be reading properly, indicating that the rear cat was functining. With a little bit of luck, I can put off the replacement of the rear pre cat for a while longer. I have no idea why it is working more effeciently now than it was a few weeks ago.