P0420 and P0430 Simultaneously

Post by **Big_Tone** » Sun Jan 14, 2024 12:46 pm

So, now that I have more or less worked through most, if not all of the issues I was experiencing with my M56, I am now getting the P0420 and P0430 simultaneously. I read in another thread that this may be due to the coolant thermostat being bad. I used my scanner to try and check it and the only thing I found that referenced temp at all is in the pic. Is this what I should look for? If so, does this look right?

Post by **mdmellott** » Sun Jan 14, 2024 9:42 pm

The CATEMP11 is the catalytic converter. bank 1/sensor 1, temperature reading from the air/fuel sensor at the input end of the cat. Downstream, there is an O2 sensor (sensor 2) that monitors the efficiency of the catalytic converter by measuring the oxygen content of the exhaust gases flowing out of the cat. When the catalyst system efficiency is below the expect threshold, P0420 (bank 1) and/or P0430 (bank 2) DTC codes will be flagged. The coolant thermostat has no effect on this nor does the coolant temperature.

Your profile indicates quite a bit of intake and exhaust modifications with PPE Headers; HPS Intake
Custom 2 1/4” exhaust with Jones Exhaust X-Pipe. I suspect your stock cats may worn out from the mods or the downstream O2 sensors have stopped functioning as they should. Checking with a better scan tool to see real time component data of everything going on would help figure this out. Your code reader is only capturing a minimal amount of component data in the freeze frame at the moment the DTC codes were flagged.

Post by **Shanehsmp** » Mon Jan 15, 2024 10:57 am

Do you have catalytic converters before your O2 sensors? If you don't, seeing as you are using PPE headers, this will always occur.

You need a defouler to trick the system. The ones I use on my M56 are only available in Canada, but I can help you get them if you need.

Post by **Big_Tone** » Mon Jan 15, 2024 4:49 pm

mdmellott wrote: ↑
Sun Jan 14, 2024 9:42 pm
The CATEMP11 is the catalytic converter. bank 1/sensor 1, temperature reading from the air/fuel sensor at the input end of the cat. Downstream, there is an O2 sensor (sensor 2) that monitors the efficiency of the catalytic converter by measuring the oxygen content of the exhaust gases flowing out of the cat. When the catalyst system efficiency is below the expect threshold, P0420 (bank 1) and/or P0430 (bank 2) DTC codes will be flagged. The coolant thermostat has no effect on this nor does the coolant temperature.

Your profile indicates quite a bit of intake and exhaust modifications with PPE Headers; HPS Intake
Custom 2 1/4” exhaust with Jones Exhaust X-Pipe. I suspect your stock cats may worn out from the mods or the downstream O2 sensors have stopped functioning as they should. Checking with a better scan tool to see real time component data of everything going on would help figure this out. Your code reader is only capturing a minimal amount of component data in the freeze frame at the moment the DTC codes were flagged.

That make sense. I was looking for the coolant temp reading and didn't see anything close to it. The only temp reading I found was this. I don't have stock cats anymore. I have hi-flow cats installed after the air/fuel sensors.

Post by **Big_Tone** » Mon Jan 15, 2024 4:51 pm

Shanehsmp wrote: ↑
Mon Jan 15, 2024 10:57 am
Do you have catalytic converters before your O2 sensors? If you don't, seeing as you are using PPE headers, this will always occur.

You need a defouler to trick the system. The ones I use on my M56 are only available in Canada, but I can help you get them if you need.

I have hi-flow cats installed after the air/fuel sensors and before the secondary o2 sensors. Which sensors need the defoulers?

Post by **Shanehsmp** » Mon Jan 15, 2024 5:06 pm

Big_Tone wrote: ↑
Mon Jan 15, 2024 4:51 pm

Shanehsmp wrote: ↑
Mon Jan 15, 2024 10:57 am
Do you have catalytic converters before your O2 sensors? If you don't, seeing as you are using PPE headers, this will always occur.

You need a defouler to trick the system. The ones I use on my M56 are only available in Canada, but I can help you get them if you need.
I have hi-flow cats installed after the air/fuel sensors and before the secondary o2 sensors. Which sensors need the defoulers?

It would be the downstream O2 sensors, the ones in the Y pipe, there's a chance the high flow cats got burnt up or that they aren't 3 way cats(only 2 way, which do not remove NOx)....were they from PPE or another manufacturer?

Post by **Big_Tone** » Mon Jan 15, 2024 5:15 pm

Shanehsmp wrote: ↑
Mon Jan 15, 2024 5:06 pm

Big_Tone wrote: ↑
Mon Jan 15, 2024 4:51 pm

I have hi-flow cats installed after the air/fuel sensors and before the secondary o2 sensors. Which sensors need the defoulers?
It would be the downstream O2 sensors, the ones in the Y pipe, there's a chance the high flow cats got burnt up or that they aren't 3 way cats(only 2 way, which do not remove NOx)....were they from PPE or another manufacturer?

I didn't get them from PPE, but they recommended I get Magnaflow 59905. They have only been on a year, so I'd be surprised if they both burned out at the same time. Not sure if they're three way or not.

Post by **mdmellott** » Tue Jan 16, 2024 8:57 am

Big_Tone wrote: ↑
Mon Jan 15, 2024 5:15 pm
Not sure if they're three way or not.

I looked up the specs. They are 3-way cats. I decent scan tool will show you how the downstream O2 sensors are behaving while the engine is running. The voltage readings that would be shown on the scan tool live data should be fairly steady. If the readings are flatlined or zero, those sensors are shot or the harness connection to them is not making contact on one or more pins.

Post by **Big_Tone** » Tue Jan 16, 2024 10:01 am

mdmellott wrote: ↑
Tue Jan 16, 2024 8:57 am

Big_Tone wrote: ↑
Mon Jan 15, 2024 5:15 pm
Not sure if they're three way or not.
I looked up the specs. They are 3-way cats. I decent scan tool will show you how the downstream O2 sensors are behaving while the engine is running. The voltage readings that would be shown on the scan tool live data should be fairly steady. If the readings are flatlined or zero, those sensors are shot or the harness connection to them is not making contact on one or more pins.

Ok, I'll take a look today to get that info. I read in another thread that sometimes the coolant thermostat goes bad, which could cause the P0420 and P0430 to simultaneously trigger. I initially was trying to get the coolant thermostat temp to see if it was in range. It's just really odd that both codes are thrown together.

Post by **mdmellott** » Tue Jan 16, 2024 8:07 pm

Big_Tone wrote: ↑
Tue Jan 16, 2024 10:01 am
I read in another thread that sometimes the coolant thermostat goes bad, which could cause the P0420 and P0430 to simultaneously trigger. I initially was trying to get the coolant thermostat temp to see if it was in range.

The coolant thermostat is a mechanical device. When it fails, it fails to open and your engine would overheat. The ECT (engine coolant temperature) sensor would be read by a decent scanner to give you its temperature indication of the coolant. If it failed, there would be another DTC indicating it had failed. If it reading wrong, and the coolant is actually much hotter or much colder than the ETC indicates, that could throw off the prescribed fuel mix by the ECM, based on a bad temperature reading, but that would make your engine run lousy. A better scan tool, than what you have, is needed to see more data.

Post by **mdmellott** » Wed Jan 17, 2024 6:52 am

mdmellott wrote: ↑
Tue Jan 16, 2024 8:07 pm
When it fails, it fails to open and your engine would overheat.

Oops! When it fails, it fails closed, not open.

.... If the ECT reading was wrong, and the coolant is actually much hotter or much colder than the ETC indicates, that could throw off the prescribed fuel mix by the ECM, based on a bad temperature reading, but that would make your engine run lousy.

It is possible that a false reading by the ECT sensor could cause a P0420 and P0430 DTC at the same time. Basically, the O2 sensors are a "witness" to what has occurred upstream. If the O2 sensors are in good working condition, the O2 sensor will react to actual conditions of air/fuel mix in the exhaust. The ECM would expect a specific reaction from the O2 sensor based, to part, on the false ECT data but since that data was a "lie", the ECM could flag the P0420 and P0430 errors.

Get a decent scan tool to verify the component data.

Post by **Big_Tone** » Thu Jan 18, 2024 5:31 pm

mdmellott wrote: ↑
Wed Jan 17, 2024 6:52 am

mdmellott wrote: ↑
Tue Jan 16, 2024 8:07 pm
When it fails, it fails to open and your engine would overheat.
Oops! When it fails, it fails closed, not open.

.... If the ECT reading was wrong, and the coolant is actually much hotter or much colder than the ETC indicates, that could throw off the prescribed fuel mix by the ECM, based on a bad temperature reading, but that would make your engine run lousy.

It is possible that a false reading by the ECT sensor could cause a P0420 and P0430 DTC at the same time. Basically, the O2 sensors are a "witness" to what has occurred upstream. If the O2 sensors are in good working condition, the O2 sensor will react to actual conditions of air/fuel mix in the exhaust. The ECM would expect a specific reaction from the O2 sensor based, to part, on the false ECT data but since that data was a "lie", the ECM could flag the P0420 and P0430 errors.

Get a decent scan tool to verify the component data.

That makes sense. When I get my car scanned with a better scan tool, what readings should I look/ask for?

Post by **mdmellott** » Thu Jan 18, 2024 8:56 pm

Different scanners sometimes have different ways of identifying the components but when you look at the live streaming data, you should be able to make sense of it. The downstream O2 sensors will be identified as something like O2B1S2 and O2B2S2, for O2 sensor, bank 1, sensor 2 and O2 sensor, bank 2, sensor 2. The ECT may simply be identified as ECT, for the engine coolant temperature sensor. Once the engine is warmed up, those downstream O2 sensors should be reading a fairly steady voltage of .45V or so. If the voltage is zero or the voltage constantly fluctuates between .1V and .9V or so, or fluctuates at all more than .2V, then those sensors have a problem with wiring or they are shot. The ECT sensor should be a temperature reading of at least 180F when the engine reaches normal operating temperature. If it does not get up to a temperature reading that is normal and it stays at a lower temperature, then the ECT sensor is probably shot.

Post by **mdmellott** » Fri Jan 19, 2024 12:31 am

Have the MAF sensor checked as well. Those are notorious for getting dirty and sending false readings on air flow and air temperature to the ECM, which in turn makes the care run lousy and could potentially trigger the P0420 and P0430 codes at the same time. Failure of the MAF sensor to be accurate is very common when intakes are modified with aftermarket cold air intakes and high flow rate air filters, especially oiled air filters like K&N.

Post by **seymore4** » Mon Jan 22, 2024 3:45 pm

Do you have emissions testing required? You need a tune... You have long tube headers, P0420/430 are to be expected.

Post by **Big_Tone** » Thu Jan 25, 2024 10:49 am

seymore4 wrote: ↑
Mon Jan 22, 2024 3:45 pm
Do you have emissions testing required? You need a tune... You have long tube headers, P0420/430 are to be expected.

Yes, I'm in Illinois and we have testing. That's somewhat of a relief to know a tune is all I need. I was getting concerned that it may be something else wrong. These are the only codes I'm getting now, so I should be ready soon. Thanks!

Post by **seymore4** » Thu Jan 25, 2024 12:48 pm

Ok so if you do have emissions testing required then you'll have to get the codes to stay off without disabling them in the tune. The tune is highly recommended to make sure it's running right and to get the most out of it, but it most likely won't solve your problem.

Post by **Big_Tone** » Sun Jan 28, 2024 10:52 am

mdmellott wrote: ↑
Fri Jan 19, 2024 12:31 am
Have the MAF sensor checked as well. Those are notorious for getting dirty and sending false readings on air flow and air temperature to the ECM, which in turn makes the care run lousy and could potentially trigger the P0420 and P0430 codes at the same time. Failure of the MAF sensor to be accurate is very common when intakes are modified with aftermarket cold air intakes and high flow rate air filters, especially oiled air filters like K&N.

I'll try to check the MAF today. Got sidetracked because my drivers exterior door handle broke last week. But... I scanned again to get more data and noticed for the heated catalyst it read N/A. Also, the coolant temp was 83º, so I'm guessing that's within range.

I have read that when the heated catalyst reads N/A that there is a procedure to reset it. Does anyone know the procedure for our cars? Could it also be a blown fuse? Any other possible causes?

Post by **Pimperish1** » Sat Feb 24, 2024 9:43 pm

mdmellott wrote: ↑
Thu Jan 18, 2024 8:56 pm
Different scanners sometimes have different ways of identifying the components but when you look at the live streaming data, you should be able to make sense of it. The downstream O2 sensors will be identified as something like O2B1S2 and O2B2S2, for O2 sensor, bank 1, sensor 2 and O2 sensor, bank 2, sensor 2. The ECT may simply be identified as ECT, for the engine coolant temperature sensor. Once the engine is warmed up, those downstream O2 sensors should be reading a fairly steady voltage of .45V or so. If the voltage is zero or the voltage constantly fluctuates between .1V and .9V or so, or fluctuates at all more than .2V, then those sensors have a problem with wiring or they are shot. The ECT sensor should be a temperature reading of at least 180F when the engine reaches normal operating temperature. If it does not get up to a temperature reading that is normal and it stays at a lower temperature, then the ECT sensor is probably shot.

I use a blue driver scan tool. Funny thing is it shows the upstream sensors with flat voltage and the down stream sensors fluctuating (with no check engine light, go figure). I've been fighting with these codes off and on for a while now. Always thought it seemed backwards, but bruh, if that light is staying off, who am I to rock the boat. Lol. The last punch thrown at those codes was replacing all the O2 sensors and spraying DPF foam cleaner in both cats. I get an occasional "rich" code in bank two followed by a catalyst efficiency code in that same bank but it's not consistent. Think my catch can install was causing a vacuum issue. Just tweaked that last weekend so we'll see....

Post by **VStar650CL** » Sun Feb 25, 2024 6:25 am

The upstreams are A/F and not HO2S (probably 2.2V types but I'd have to look it up). A/F's don't oscillate, they're direct-reading with voltages below nominal being rich and above nominal being lean.

Post by **Pimperish1** » Mon Feb 26, 2024 1:38 am

VStar650CL wrote: ↑
Sun Feb 25, 2024 6:25 am
The upstreams are A/F and not HO2S (probably 2.2V types but I'd have to look it up). A/F's don't oscillate, they're direct-reading with voltages below nominal being rich and above nominal being lean.

I see.... Wasn't sure if I was interpreting it right as far as being "normal" or not. But that light stayed off so well enough was gonna get left alone. Lol. I did notice they would peak when I lifted off the throttle, so that aligns with what your saying. Makes more sense now.
So the downstreams are supposed to bee-bob back and forth?

Post by **VStar650CL** » Mon Feb 26, 2024 7:52 am

Correct. The A/F's always spike rich on throttle-up and then lean on drop-throttle. That's a normal response to inertia in the intake airstream. People don't tend to think of air as Newtonian, but yes, Virginia, the moving mass tends to remain in motion and the static mass tends to remain static. What that means in practice is whatever reaches the exhaust is always lagging a step behind what the injectors are doing.

P0420 and P0430 Simultaneously

P0420 and P0430 Simultaneously

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