p0420 and p0430 even after brand new gm cats
08-23-2007, 12:58 AM
#1
p0420 and p0430 even after brand new gm cats Had codes p0420 and p0430 pop up. Took it to the dealer and they replaced the cats under warrenty. Picked the car up right at closing, got 5 miles down the road and the same codes popped up again. From searching everthing I've read has shown it to be the cats. Could it be an o2 sensor problem on both banks?
The car is bone stock btw.
The car is bone stock btw.
08-23-2007, 07:44 PM
#3
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Originally Posted by promod1955
Took it back today and turns out there was a problem with the pcm. Put a new one in and its been flawless so far.
How much did you pay to change the PCM? I may have the same problem.
08-23-2007, 08:00 PM
#4
TECH Senior Member
Could be wrong but don't see the PCM generally being the problem with cat inefficiency codes, not even in the diagnosis flow charts? Cruz28 according to the federal emissions warranty booklet that came with my car the PCM is covered for 8 years/80k.
08-23-2007, 08:17 PM
#5
That dont sound right.
Both codes are set if the rear 02s mimic the front 02s in voltage waveform. I have o'scope screen shots of just this situation.
Before it ever runs these monitors it needs to test and pass other ones. If there is a failure somewhere else, it wont even run/test/pass/fail the catalyst.
Never heard of a PCM issue causing these codes.
Right out of ALLDATA
conditions for setting the DTC
The PCM determines the oxygens storage capability of the catalytic converter has degraded below a calibrated threshold.
Hence the rear 02s mimicking the fronts.
Diagnostics, ahhhh, one of my fortes.
PS. How ya doin Robbie?
Both codes are set if the rear 02s mimic the front 02s in voltage waveform. I have o'scope screen shots of just this situation.
Before it ever runs these monitors it needs to test and pass other ones. If there is a failure somewhere else, it wont even run/test/pass/fail the catalyst.
Never heard of a PCM issue causing these codes.
Right out of ALLDATA
conditions for setting the DTC
The PCM determines the oxygens storage capability of the catalytic converter has degraded below a calibrated threshold.
Hence the rear 02s mimicking the fronts.
Diagnostics, ahhhh, one of my fortes.
PS. How ya doin Robbie?
08-23-2007, 08:59 PM
#6
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Originally Posted by edcmat-l1
That dont sound right.
Both codes are set if the rear 02s mimic the front 02s in voltage waveform. I have o'scope screen shots of just this situation.
Before it ever runs these monitors it needs to test and pass other ones. If there is a failure somewhere else, it wont even run/test/pass/fail the catalyst.
Never heard of a PCM issue causing these codes.
Right out of ALLDATA
conditions for setting the DTC
The PCM determines the oxygens storage capability of the catalytic converter has degraded below a calibrated threshold.
Hence the rear 02s mimicking the fronts.
Diagnostics, ahhhh, one of my fortes.
PS. How ya doin Robbie?
Both codes are set if the rear 02s mimic the front 02s in voltage waveform. I have o'scope screen shots of just this situation.
Before it ever runs these monitors it needs to test and pass other ones. If there is a failure somewhere else, it wont even run/test/pass/fail the catalyst.
Never heard of a PCM issue causing these codes.
Right out of ALLDATA
conditions for setting the DTC
The PCM determines the oxygens storage capability of the catalytic converter has degraded below a calibrated threshold.
Hence the rear 02s mimicking the fronts.
Diagnostics, ahhhh, one of my fortes.
PS. How ya doin Robbie?
General Description:
In order to maintain a reasonably low emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), the engine controls system uses a three-way catalytic converter. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas. This reaction converts them into harmless water vapor and Carbon Dioxide. The catalyst also reduces NOx, converting it to Nitrogen. The PCM monitors this process using Bank 1 HO2S #2. Bank 1 HO2S #2, located in the exhaust stream past the three-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalysts ability to convert exhaust emissions effectively. If the catalyst is functioning correctly, the Bank 1 HO2S #2 signal will be far less active than that produced by Bank 1 HO2S #1. This indicates that the three-way catalytic converters oxygen storage capacity is below a threshold considered acceptable.
For complete diagnostic steps you can read here.
08-23-2007, 09:42 PM
#7
What doesnt sound right? The pcm was making the car way to rich and the rear 02 sensors picked up all the extra fuel going through them, like there suppose to, getting my below threshold codes. I put 155 miles on it today and everythings fine. None of the 02's were changed. Im sure this isn't a common problem for these cars.
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08-24-2007, 10:19 AM
#9
Originally Posted by promod1955
What doesnt sound right? The pcm was making the car way to rich and the rear 02 sensors picked up all the extra fuel going through them, like there suppose to, getting my below threshold codes. I put 155 miles on it today and everythings fine. None of the 02's were changed. Im sure this isn't a common problem for these cars.
If it were as simple as the computer adding too much fuel, it would most likely set rich bank one and two codes. P0172/P0175
The catalyst efficiency codes are very specific. All obd2 codes are very specific for that matter.
I guess I could see the pcm's threshold voltage being too low, or too high, whatever, and it interpreting the input wrong. But even that, shouldnt take a pcm replacement, only a flash. Never heard of a LS computer going bad, and causing a false code. If they're functioning and running the car, they're ok, and probably only need a flash.
These computers are very, very reliable.
08-24-2007, 11:27 AM
#11
Originally Posted by promod1955
You make some great points, and I agree with them. I would have never thought this would of been the problem, but hey its fixed. 
08-25-2007, 11:01 AM
#13
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Originally Posted by 2001NBMZ28
Could be wrong but don't see the PCM generally being the problem with cat inefficiency codes, not even in the diagnosis flow charts? Cruz28 according to the federal emissions warranty booklet that came with my car the PCM is covered for 8 years/80k.
08-25-2007, 02:23 PM
#14
This is a scope shot of an upstream and downstream 02 (lower wave is upstream, top wave is downstream). This is what they look like before the cat lights off. Its also what they look like when the cat is bad. Notice how they have almost exactly the same waveform. Same voltage differential, same frequency.
This is what they look like after tha cat has lit off. Or turned on, however you wanna state it. At this point, the cat is storing 02, evidenced by the steady high voltage (.700-.800v). Its not rich, its oxygen deplete.
This is what it looks like upon deceleration. you can see by the drop in voltage in the bottom waveform, which is the upstream, the car has went into DFCO (deceleration fuel cutoff), followed shortly by the drop in downstream 02 voltage, which means the cat went from storing 02 to releasing. Working just as it should. This is actually part of the cat efficiency test also. Dont remember the time period, but the computer wants to see a time delay between DFCO and the corresponding drop in rear 02 voltage, indicating the store and release ability of the cat.
This is the information your computer sees and wants to see, in raw form. not viewed thru a scanner which slows it down and actually 'filters' it.
This is the only way to properly diagnose, evaluate, and pass or fail a catalyst system. Anything short of monitoring up and downstream 02s with a scope, is just guessing.
And remember, obd2 systems are very specific about what failures are what. If its running rich or lean, it will know that, and flag accordingly. If the 02s themselves fail, it will know that too. All of these failures are separated by different pass/fail criteria.
99 times out of a hundred, if not 100 times out of 100, a catalyst failure code is a catalyst failure. Some of the ones setting PO420/430 with new cats are probably caused by low quality cats, not living up to the PCMs standards. These computers are very smart, and are looking for very specific things when it comes to passing of failing certain tests. The catalyst monitor is looking for criteria based on amplitude, and frequency. Thats is, how high of a voltage, and how long it takes to rise and fall during storage and release of oxygen.
This is what they look like after tha cat has lit off. Or turned on, however you wanna state it. At this point, the cat is storing 02, evidenced by the steady high voltage (.700-.800v). Its not rich, its oxygen deplete.
This is what it looks like upon deceleration. you can see by the drop in voltage in the bottom waveform, which is the upstream, the car has went into DFCO (deceleration fuel cutoff), followed shortly by the drop in downstream 02 voltage, which means the cat went from storing 02 to releasing. Working just as it should. This is actually part of the cat efficiency test also. Dont remember the time period, but the computer wants to see a time delay between DFCO and the corresponding drop in rear 02 voltage, indicating the store and release ability of the cat.
This is the information your computer sees and wants to see, in raw form. not viewed thru a scanner which slows it down and actually 'filters' it.
This is the only way to properly diagnose, evaluate, and pass or fail a catalyst system. Anything short of monitoring up and downstream 02s with a scope, is just guessing.
And remember, obd2 systems are very specific about what failures are what. If its running rich or lean, it will know that, and flag accordingly. If the 02s themselves fail, it will know that too. All of these failures are separated by different pass/fail criteria.
99 times out of a hundred, if not 100 times out of 100, a catalyst failure code is a catalyst failure. Some of the ones setting PO420/430 with new cats are probably caused by low quality cats, not living up to the PCMs standards. These computers are very smart, and are looking for very specific things when it comes to passing of failing certain tests. The catalyst monitor is looking for criteria based on amplitude, and frequency. Thats is, how high of a voltage, and how long it takes to rise and fall during storage and release of oxygen.
08-25-2007, 08:06 PM
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Originally Posted by edcmat-l1
This is a scope shot of an upstream and downstream 02 (lower wave is upstream, top wave is downstream). This is what they look like before the cat lights off. Its also what they look like when the cat is bad. Notice how they have almost exactly the same waveform. Same voltage differential, same frequency.
This is what they look like after tha cat has lit off. Or turned on, however you wanna state it. At this point, the cat is storing 02, evidenced by the steady high voltage (.700-.800v). Its not rich, its oxygen deplete.
This is what it looks like upon deceleration. you can see by the drop in voltage in the bottom waveform, which is the upstream, the car has went into DFCO (deceleration fuel cutoff), followed shortly by the drop in downstream 02 voltage, which means the cat went from storing 02 to releasing. Working just as it should. This is actually part of the cat efficiency test also. Dont remember the time period, but the computer wants to see a time delay between DFCO and the corresponding drop in rear 02 voltage, indicating the store and release ability of the cat.
This is the information your computer sees and wants to see, in raw form. not viewed thru a scanner which slows it down and actually 'filters' it.
This is the only way to properly diagnose, evaluate, and pass or fail a catalyst system. Anything short of monitoring up and downstream 02s with a scope, is just guessing.
And remember, obd2 systems are very specific about what failures are what. If its running rich or lean, it will know that, and flag accordingly. If the 02s themselves fail, it will know that too. All of these failures are separated by different pass/fail criteria.
99 times out of a hundred, if not 100 times out of 100, a catalyst failure code is a catalyst failure. Some of the ones setting PO420/430 with new cats are probably caused by low quality cats, not living up to the PCMs standards. These computers are very smart, and are looking for very specific things when it comes to passing of failing certain tests. The catalyst monitor is looking for criteria based on amplitude, and frequency. Thats is, how high of a voltage, and how long it takes to rise and fall during storage and release of oxygen.
This is what they look like after tha cat has lit off. Or turned on, however you wanna state it. At this point, the cat is storing 02, evidenced by the steady high voltage (.700-.800v). Its not rich, its oxygen deplete.
This is what it looks like upon deceleration. you can see by the drop in voltage in the bottom waveform, which is the upstream, the car has went into DFCO (deceleration fuel cutoff), followed shortly by the drop in downstream 02 voltage, which means the cat went from storing 02 to releasing. Working just as it should. This is actually part of the cat efficiency test also. Dont remember the time period, but the computer wants to see a time delay between DFCO and the corresponding drop in rear 02 voltage, indicating the store and release ability of the cat.
This is the information your computer sees and wants to see, in raw form. not viewed thru a scanner which slows it down and actually 'filters' it.
This is the only way to properly diagnose, evaluate, and pass or fail a catalyst system. Anything short of monitoring up and downstream 02s with a scope, is just guessing.
And remember, obd2 systems are very specific about what failures are what. If its running rich or lean, it will know that, and flag accordingly. If the 02s themselves fail, it will know that too. All of these failures are separated by different pass/fail criteria.
99 times out of a hundred, if not 100 times out of 100, a catalyst failure code is a catalyst failure. Some of the ones setting PO420/430 with new cats are probably caused by low quality cats, not living up to the PCMs standards. These computers are very smart, and are looking for very specific things when it comes to passing of failing certain tests. The catalyst monitor is looking for criteria based on amplitude, and frequency. Thats is, how high of a voltage, and how long it takes to rise and fall during storage and release of oxygen.
08-25-2007, 09:25 PM
#16
Originally Posted by Cruz28
Thanks for the info, makes perfect sense. I forgot how specific these computers were. I still want to do a dyno tune though. Do you think I could do the dyno tune before I buy new cats? Which brand of cats is best to have a shop weld into the y pipe in place of the ones that are now there?
As for brand cats, I would go with OEs if you can afford them. If not, at least go with a name brand, but you will still probably have issues with them. I've seen so many cars, LS powered or not, have trouble with non-OE cats and catalyst effiency codes.
08-27-2007, 03:52 AM
#17
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First thing I do when I get 0430 or 0420 is look at the appropriate 02 sensor and just see if they are switching.
Front 02's should switch constantly,rear 02's should be constant basically. It give's you a good indication,if you have a wideband you can check at the tailpipe also.
I'm curious of the computer failure,the tech must have measured the pinout voltage's of the PCM to determine that it failed. I wonder as to what he found.
I know firsthand that if a tech can't explain it or figure it out,they will sometimes just replace a likely part right off the bat.(especially under warranty)
I second what he said about going with OE's,with the kind of warranty you have there's no reason not too. And not all cat's are equal,some universal's will have differing amount's of catlyst inside that isn't necessarily up to parr with OE standards.
Front 02's should switch constantly,rear 02's should be constant basically. It give's you a good indication,if you have a wideband you can check at the tailpipe also.
I'm curious of the computer failure,the tech must have measured the pinout voltage's of the PCM to determine that it failed. I wonder as to what he found.
I know firsthand that if a tech can't explain it or figure it out,they will sometimes just replace a likely part right off the bat.(especially under warranty)
I second what he said about going with OE's,with the kind of warranty you have there's no reason not too. And not all cat's are equal,some universal's will have differing amount's of catlyst inside that isn't necessarily up to parr with OE standards.
09-01-2007, 12:05 PM
#18
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If I buy OE cats then I would have to purchase shorties because they won't fit the mid length headers the way they come. I don't want to spend over a grand on the OE cats to cut and weld them into my current y pipe. Does anyone know what brand of aftermarket cats are up to par with the originals? Does GM sell the cats without the y pipe? Last time I checked each GM cat comes welded to part of the y pipe.
09-01-2007, 01:02 PM
#19
Originally Posted by Cruz28
If I buy OE cats then I would have to purchase shorties because they won't fit the mid length headers the way they come. I don't want to spend over a grand on the OE cats to cut and weld them into my current y pipe. Does anyone know what brand of aftermarket cats are up to par with the originals? Does GM sell the cats without the y pipe? Last time I checked each GM cat comes welded to part of the y pipe.
If you wanna keep the downstreams active, for whatever reason, the best aftermarket cats I have found are the magnaflow hi-flow cats. The seem to work the best, as far as staying on as their temperature drops a little at idle, and overall same storage and release of 02, resulting in the same, or very similar voltage waveforms as OE cats.
09-02-2007, 01:02 AM
#20
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Originally Posted by edcmat-l1
If you're modded, that is headers and a tune, turn off the codes.
If you wanna keep the downstreams active, for whatever reason, the best aftermarket cats I have found are the magnaflow hi-flow cats. The seem to work the best, as far as staying on as their temperature drops a little at idle, and overall same storage and release of 02, resulting in the same, or very similar voltage waveforms as OE cats.
If you wanna keep the downstreams active, for whatever reason, the best aftermarket cats I have found are the magnaflow hi-flow cats. The seem to work the best, as far as staying on as their temperature drops a little at idle, and overall same storage and release of 02, resulting in the same, or very similar voltage waveforms as OE cats.