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2001ZR2 the big reason for using Torque Pro for this, is that it will plot more than one PID on the same graph at the same time. A very nice feature when you need it. Otherwise Car Gauge Pro does a lot more. For the price, anyone considering this should get both.
WTF???
replaced the cats, re-set codes, waited for I/M readiness (smog check) to run... and BLAM, as soon as the cat cleared green on I/M readiness the P0420 code popped again.
Anybody have any ideas as to what else could pop it?
Oxygen sensors all passed checks, the only thing not passing the check is the secondary air.
WTF???
replaced the cats, re-set codes, waited for I/M readiness (smog check) to run... and BLAM, as soon as the cat cleared green on I/M readiness the P0420 code popped again.
Anybody have any ideas as to what else could pop it?
Oxygen sensors all passed checks, the only thing not passing the check is the secondary air.
Damn! The description for the test the PCM does for the P0420 is below. Maybe pull off a vacuum hose to create a leak (or give a shot of propane into the intake depending on where the post-cat O2 sensor is running) and look at the time delay for the post-cat sensor to cross 0.45v in the plots? If a cat is bad or marginal, there is less or no delay. If you can wait, I'll try it this weekend to have reference to a vehicle that is not setting a P0420. Are you trying to pass the emissions readiness for your state tags?
Supposedly, all that can cause the P0420 is O2 sensors, cat converter, or exhaust leak. Some people report non-factory cats giving problems, but I think this may be more of an excuse.
Another thing you might do with the Car Gauge Pro is to log the O2 sensors to a file for long enough to catch what is happening during the P0420 test that fails. That might shed some light on what is happening.
good luck and let me know if you want me to go down this path with you.
CIRCUIT DESCRIPTION
This diagnostic test is designed in order to measure the efficiency of the Three-way Catalytic Converter (TWC) system. Catalytic convertor efficiency is a measure of its ability to store oxygen after converting the levels of Hydrocarbon (HC) , Carbon Monoxide (CO) , and Oxides Of Nitrogen (NOx) to less harmful gases. The control module is able to evaluate the catalyst efficiency once the vehicle has met the enable criteria and the vehicle is at idle instead of the steady cruise speeds used in the past. Once the conditions for running this Diagnostic Trouble Code (DTC) are met, the control module commands either a lean or rich air/fuel ratio depending on the current state of the exhaust oxygen level. The control module issues a rich command if the exhaust is currently lean, or a lean command if the exhaust is currently rich. After completion of the first command, a second and opposite command is issued.
For example, if the control module were to command a rich mixture, the upstream Heated Oxygen Sensor (HO2S) voltage would increase immediately. The rich mixture is delayed in reaching the downstream HO2S due to the conversion process occurring within the converter. The higher the efficiency, the more the delay before the rich or lean mixture is detected by the downstream Oxygen (O2) sensor. As a result of the lower conversion efficiency within a damaged or poisoned catalyst, the delay in the rich or lean mixture reaching the downstream O2 sensor is significantly shorter. This DTC monitors the amount of time required for both the upstream and downstream HO2S voltages to cross a calibrated voltage threshold in response to the rich or lean command.
Ya, my registration is 10 days past due, need to smog.
I read another article that said some of these blazers would trow the P0420 if the the internal cylinder temp is too high relating in more hydrocarbons in exhaust, which is a result of bad plugs.
Ever hear of anything like that?
Might just need to take it to an exhaust shop and get it figured out, I hope not, already thrown too much money at this thing with the cats already.
Ya, my registration is 10 days past due, need to smog.
I read another article that said some of these blazers would trow the P0420 if the the internal cylinder temp is too high relating in more hydrocarbons in exhaust, which is a result of bad plugs.
Ever hear of anything like that?
Might just need to take it to an exhaust shop and get it figured out, I hope not, already thrown too much money at this thing with the cats already.
I would think the only way to get to a too-high cylinder temp would be too lean of mixture, which would end up with extra oxygen not hydrocarbons. But I didn't fix your P0420 with the cats, so guess I don't know everything either!! I'll try the rich/lean thing I suggested this weekend, and post my results. That's the only way that I know to go about helping you. I read that a bad o2 sensor could cause it too, but I really am against replacing O2 sensors *****-nilly. But other than exhaust leak I think that might be your only possibility.
does the P0420 always come on right after the catalyst emission readiness test passes? I would think that a pass would indicate that it was OK.....
If you're having trouble getting the A.I.R. system to complete it's emission readiness testing (with SES light off), several people now have had bad thermostats not allowing the engine to get hot enough for this particular test to run. I believe SES light on prevents the tests from running, so when Po420 sets all bets are off for the emissions readiness tests. You then have to clear the codes and start the emissions readiness tests over from the beginning.
I would think the only way to get to a too-high cylinder temp would be too lean of mixture, which would end up with extra oxygen not hydrocarbons. But I didn't fix your P0420 with the cats, so guess I don't know everything either!! I'll try the rich/lean thing I suggested this weekend, and post my results. That's the only way that I know to go about helping you. I read that a bad o2 sensor could cause it too, but I really am against replacing O2 sensors *****-nilly. But other than exhaust leak I think that might be your only possibility.
does the P0420 always come on right after the catalyst emission readiness test passes? I would think that a pass would indicate that it was OK.....
If you're having trouble getting the A.I.R. system to complete it's emission readiness testing (with SES light off), several people now have had bad thermostats not allowing the engine to get hot enough for this particular test to run. I believe SES light on prevents the tests from running, so when Po420 sets all bets are off for the emissions readiness tests. You then have to clear the codes and start the emissions readiness tests over from the beginning.
Good luck and let me know if I can help.
Yah, the code pops within seconds of the cat passing the I/M readiness, so I don't think it's the new cats.
This is frustrating.
The fuel millage is really low too, so maybe running rich.
Can you explain how to run the test on torque that you were talking about?
I’m pretty sure once reset the system has to run so many miles for so much time and reach x temp before it everything says ready I just cant recall the amounts but I do remember reading it. I know my 98 has those same two “X” on my little pocket Autel AL329 scan tool currently and was recently reset.
03-16-2019, 10:47 PM
