Topic: P0420 Catalyst System Low Efficiency

[sunnygator]

Leaving Joe's today, and noticed my CEL was on.  The code was P0420 Catalyst System Low Efficiency, and another P0420 Catalyst System Low Efficiency was pending.  Now I installed heated seats this weekend.   Even a non-gearhead like me is pretty confident they don't have anything to do with the exhaust.  That said, I wondered if having the car electrical harness disconnected from the BCM to install the heated seats to the fuseblock didn't reset something?  Anyway I cleared the code (btw I love Rev on my iPod) and drove the 2 1/2 hours home, pushed it several times, and the CEL is not back........


Any thoughts?

sunnygator

[2kwk4u]

I really doubt unplugging that BCM connector could possibly trigger a cat efficiency code.  As I understand it, that info is processed in the ECM, vice the BCM.  Even though they're on the same databus, I've never experienced, or heard of unplugging/reconnecting a connector causing false codes.

Your exhaust is all stock, isn't it?  Do you recall dragging it or bottoming out on anything recently?  It might be worth checking into to see if you might have an exhaust leak, or if one of your 02 sensor wires have come loose.  I'm not familiar with Rev, but from what I remember, it's pretty powerful.  Can you use it to monitor/log individual PIDs?  If so, you should be able to check the outputs of both O2 sensors to see what's going on. 

Even though the code didn't come back after your cleared it, you may not be "in the clear" yet.  Certain parameters have to be met for the monitor checks to run.  That code might come back next time the monitor runs - it's quite possible that it didn't run at any point during your drive home.

Here's a link that might help you:

http://www.aa1car.com/library/p0420_dtc.htm

[sunnygator]

I did hit a piece of tire tread about 3 weeks ago.  I will take a look.  Thanks again, your help this weekend was very much appreciated and very much needed too!

sunnygator

[scanner]

2kwk4u is correct, the BCM is not in the mix. The ECM expects that the Pre catalyst O2 is very active and the post catalyst O2 is not when they and the Cat are fully warmed up.  The pre cat O2 "sees" the normal too rich/too lean cycles of the engine management system.  The post cat O2 "sees" less swings in voltage output because a properly working Cat smothes the swings out.  An exhaust leak or a bad Cat are a likely cause.  Cat warranty for a non modified car is normally 8y/80,000m. Just remember Cats are killed, they don't just die.

[sunnygator]

Well a quick look shows no damage to anything under the car, and yes I have the stock exhaust. 

Still no code or pending code. 

Also Rev can check the Catalyst "readiness" monitor which was all green (good).  But it can't check the current readings on the sensors.

I will keep tabs on it, and if it comes back, then I'll be visiting my dealer. 

Thanks for the link!

sunnygator

[scanner]

I/M  Readiness monitors mean diagnosed. They do not indicate passed or failed.  So both passed tests and failed can set the I/M flag to ready. P0420 will take several trips to fail.   

[sunnygator]

Well I found out that Rev can log "freeze frame" data.  When a fault occurs, OBD II logs a code and records all related sensor values at that moment for later analysis.

Now I cleared the code before, so that freezeframe is gone, but I will check it if it comes back again.....

[scanner]

The Freeze Frame is keyed to the lamp. That is, there is no Freeze Frame stored until the lamp is requested. The parameters stored are specified by California ARB and EPA, they are not all parameters related to the DTC. Instead they are a single snapshot record of the driving conditions when the lamp was requested. They include things like vehicle speed, coolant temp, engine load, engine speed and such.  Very general, not specific to Catalyst or O2 etc.  There are many on board diagnostics that can request the lamp - known industry wide as the MIL, Malfunction Indicator Lamp - specified by California ARB & EPA.

GM does make an additional snapshot available.  That snapshot is called a Failure Record. The Failure Record is snapped on the last setting of the DTC, regardless if the lamp was requested. Sometimes there is more information than the Freeze Frame that is intended to help technicians.  Once again it is not expected to isolate a fault, but rather capture the driving conditions.  Additional data is often things like the number of miles traveled since first fault and last fault.      

So in your P0420 case the EMS requires two consecutive failures to set the lamp.  This means two trips where the diagnostic finds a fault.  This is known as a type B fault.  A type A fault sets the lamp on only one fault.  So in your case if the EMS finds a fault it will set the DTC to history and stores a Failure Record, the lamp is off.  Only on the second consecutive diagnostic that fails is the lamp on and a Freeze Frame stored.  

In summary the Failure Record has the driving conditions when the DTC last set. The Freeze Frame has the record when the lamp was requested. The Freeze Frame will not be replaced except by Misfire or Fuel Trim DTCs. It will be cleared on ECM or TCM DTC clear.  Each ECM can have only one Freeze Frame and up to five Failure Records.  

I think that is enough for now.  There is a lot more, exceptions, special cases etc....  Post your questions and if I can help, I will.  All these data require a scan tool to retrieve them.

Scanner    

[sunnygator]

When I asked Rev for a freezeframe, it told me that none had been recorded.  I assumed I'd cleared it when I cleared the code, but there was none nonetheless.

No issues today, no CEL, no codes. 

I realize it might take quite e few trips/key cycles and various driving conditions to come back (or not), so I know I'm not out of the woods.

[shabby]

Any exhaust mods?

[sunnygator]

Any exhaust mods?

No, got stock exhaust, never touched it....

[scanner]

Sounds like the lamp is out now so just drive it and enjoy. Note that the P0420 takes time to fail and at least two trips so it is very unlikely something happend at Joe's.

[DeepBlueGXP]

Great info Scanner, thanks

[sunnygator]

it is very unlikely something happend at Joe's.

Well a lot happened at Joe's but nothing to my exhaust!  Unless, of course, I find a socket in it....

[Critterman]

Those sockets have a way of showing up in the strangest places.

[sunnygator]

Well it took almost two weeks of driving, but the 0420 code came back today. 

I will call the dealer tomorrow.....

In all other ways, the car seems to be running great

sunnygator

[scanner]

Blame on-board filter calculator for being slow, or thank it for being patient, your call.  It is very carefully trying to make very certain there is problem before requesting the MIL. It looks like it finally reached the conclusion that the on-board O2 sensors indicate that the catalyst is not working well enough.  It might be the Cat, if so they are killed, they do not die of old age.  It could also be an exhaust leak, or other engine controls condition causing the O2 sensors to fail the test.  If there are tuner parts or calibrations look at these first.  Otherwise the catalyst is 8/80 warranty by federal law.

Looking at the O2 sensors voltage activity with a scan tool will tell a lot very fast. O2-1 is active when hot, O2-2 is not active when it and the Cat are hot. This is very simplified, if you have access to a scan tool with ECM data and need more analysis ideas ask. Scanner 

[2kwk4u]

Have you heard/smelled an exhaust leak?  Check the nuts at the turbo-to-cat flange.  It's not uncommon for those to work themselves loose.  If you have an exhaust leak there, you should see some carbon build-up around it. 

As scanner says, if it's your cat, that usually points to another problem.  However, if I recall correctly there has been at least one batch of bad cats that were prone to self-destruct.  I can't remember whether it was N/A cars or GXP's... I know that's not much help  I think when that happened the problems were bigger than just cat efficiency codes, though. 

[Critterman]

If I remember correctly, I think it is both, I know that the N/A's ate some stock cats

[sunnygator]

Well I haven't heard or smelled anything. 

Left it at the dealer today.  For what its worth, the tech at the dealer's main suspicion given 0420 is the CAT itself, and he said "they don't make 'em like they used to."  I suggested an exhaust leak or O2 sensor issue - his thought was that other/additional codes would be thrown.  Of course this is all way to preliminary, they will check it out tomorrow, I'll report back.

[scanner]

SunnyGator, Your tech is correct, look at the other DTCs. They are upstream, you know what travels down stream.  The P0420 on-board tests are very very smart, yet they can be tricked so look at the inputs, O2-1 and O2-2.  

They might look okay, lets look at their influences - O2 in the exhaust stream.   Exhaust gases are made of many things, a very small percent is O2, the preCat O2 verifies this, if the the postCast O2 sensor reports less O2 then the Cat is coverting HC & CO to H2O, CO2 & H2.  If not the ECM reports the issue by the MIL and DTC. A skilled diagnostic technician will verify O2 performance since they are a primary input to the P0420 on-board test.

ICE 02 sensors can be influenced by electrical problems like poor grounds and bad heaters. Also mechanical problems that influence combustion quality or exhaust aftertreament like AIR.  Look for those other DTCs too.

scanner
 

[sunnygator]

Well the dealer is ordering a new CAT.

They cleared the code for now, and told me it will take a week or so to get the part.  I wasn't able to get more info today, they were kinda busy.  The pick up slip doesn't give any other new info either.

[DeepBlueGXP]

I have a bunch laying around the house

[scanner]

The wild CAT here is keeping the rabbits away, that is, I have a good Cat at no cost. I hope your next CAT is good and at no cost too.

[sunnygator]

Everybody wants a brand new CAT,
'cause havin' a CAT
is where it's at