obd 2 trouble code p0420 problem
Thread Starter
Joined: Aug 2009
Posts: 7
From: Georgia
obd 2 trouble code p0420 problem
I have a 2007 ford mustang and I been having this code pop up p0420 Catalyst System Efficiency Below Threshold (Bank 1). I take really great care of my car and this is botherin me. My car still moving like a champ so I'm assuming its a minor problem.
I have shorty headers and pypes exhaust with mufflers deleted. Im tryna figure out if its an 02 sensor or a bad catylitic converter which I hope not. has anyone else had this problem?
I have shorty headers and pypes exhaust with mufflers deleted. Im tryna figure out if its an 02 sensor or a bad catylitic converter which I hope not. has anyone else had this problem?
5th Gear Member
Joined: May 2007
Posts: 2,388
From: Central Texas
Do you have hi-flow cats?
I get this, too, and have dug into the cause in extensive detail.
Another person who had the problem resolved it by backing-out the rear o2 sensor so it isn't so deep in the pipe, so it doesn't get as much of the flow. He used a spark plug space to maintain the seal. Interesting solution.
Another thing I was going to try (and still might), is to put in a very simple circuit modification (a 1 megaohm resistor and a 1 microfarad capacitor) to alter the signal being fed back to the ecu.
The cause. OBDII monitor test (mode 06 pid 21) measures the number of pulses read from the rear o2 sensors, and accumulates counts of those pulses over time. The pid also has defined a maximum value, which for some unknown reason, is lower on the passenger side (the side you're seeing the code for) vs. the driver side. Over a couple of driving cycles, the counts get exceeded and a cel is thrown.
If you look at a datalog of the rear sensors, you'll see the signals closely follow the front o2 signals. But the problem is the amplitude of the signal; if a cat is worn out or missing, or passing too much unmodified air, the amplitude will be too low in spikes, and those count up and cause problems.
I think part of the problem is moving the cats farther downstrea and using headers that cools down the air more as well.
Of course, you can easily rule out the sensor by swapping it with the driver side (rear sensor as well). If the sensor is bad, you'll get a p0430 instead.
I get this, too, and have dug into the cause in extensive detail.
Another person who had the problem resolved it by backing-out the rear o2 sensor so it isn't so deep in the pipe, so it doesn't get as much of the flow. He used a spark plug space to maintain the seal. Interesting solution.
Another thing I was going to try (and still might), is to put in a very simple circuit modification (a 1 megaohm resistor and a 1 microfarad capacitor) to alter the signal being fed back to the ecu.
The cause. OBDII monitor test (mode 06 pid 21) measures the number of pulses read from the rear o2 sensors, and accumulates counts of those pulses over time. The pid also has defined a maximum value, which for some unknown reason, is lower on the passenger side (the side you're seeing the code for) vs. the driver side. Over a couple of driving cycles, the counts get exceeded and a cel is thrown.
If you look at a datalog of the rear sensors, you'll see the signals closely follow the front o2 signals. But the problem is the amplitude of the signal; if a cat is worn out or missing, or passing too much unmodified air, the amplitude will be too low in spikes, and those count up and cause problems.
I think part of the problem is moving the cats farther downstrea and using headers that cools down the air more as well.
Of course, you can easily rule out the sensor by swapping it with the driver side (rear sensor as well). If the sensor is bad, you'll get a p0430 instead.
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