LTKNT101

Hey guys I'm hoping someone out there has ran into this problem I am having with my car and has found a solution. First of all, I am the proud owner of a 2001 Pontiac Trans Am WS6 coupe with 280,000+ original miles. Still runs like a champ.

It is smog time again and I have been hard at work trying to get the car in shape to pass the emissions test. The pesky codes I was struggling with were P410 (Secondary Air System), P420 (Catalyst Below Efficiency) and P440 (Evap System Leak). The PCV tube had deteriorated and broke apart in 3 sections creating a huge vacuum leak. I replaced the complete PCV assembly which included the valve, rubber grommet, and tube. I also replaced the 8 intake manifold gaskets, and the airflow absolute pressure sensor. I rest the monitors and was pleased to see that P410 and P440 did not return. A few days later, P420 set. I did some engine diagnosing and determined that cylinder low compression was the cause of the P420 code. I got a bottle of Engine Restore V8 formula and added to the engine oil as I changed it. I replaced the oil filter and reset the monitors. P420 did not return. I noticed improvements in power and idle which indicated that the engine restore formula was working as advertised to improve compression. (I am aware that simply adding fresh oil to an engine improves compression). After just two drive cycles, 20 total miles driven after being reset, 7 of the eight monitors returned to 'Complete' status leaving only the evap monitor incomplete. No codes were detected!

Not knowing how long this perfect running condition would last, I rushed to the smog shop only to be told that the part numbers on my catalytic converters were no longer valid! The car failed the test because California decided to change the part numbers for all converters made after 2013. Around 75 miles driven since resting the monitors, the check engine lamp lit again, cause: P440! I realized that either a new leak in the system had opened, or I had not fully taken care of the problem as I had thought.

I spent $500 dollars on two new California valid catalytic converters. As I drove away from the muffler shop, the car started running rough and low on power. The check engine light began to flash indicating a random misfire had occurred. This set a P300 code. I deduced that this happened because the car had sat on the lift in the muffler shop with the old catalytic converters removed for two hours while the tech waited for the new ones to arrive. Air most likely found it's way into the exhaust system and had to be flushed out. I reset the monitors and conducted the drive cycle again.

This time at total miles driven, 5 of 8 monitors were completed. The catalyst monitor, o2 heater monitor and evap monitor remained incomplete. It occurred to me that the fuel level was below the requirement of between 70 and 30 percent full when I conducted the drive cycle. I added enough gas to get the gauge needle at 70 percent full. The next morning I went through the drive cycle again. The catalyst monitor set bringing the complete total of complete monitors to 6. I was startled to see that the O2 monitor had not been completed as it did before. I took the car to 45 miles past monitor reset. The O2 heater monitor remained incomplete. Without that monitor ready, I could not go back to the smog shop. At 56 miles the check engine lamp lit. P440 again. The evap monitor had completed which gave me 7 ready monitors but now the check engine light was on and a code was stored. Can't go to the smog shop like that. I reset the monitors again. It was painfully clear that the evap leak remained. However it took on average between 30 and 70 miles For the ECM to set the code. If I could get the O2 monitor to complete along with the other 6 monitors in that window of opportunity, I could pass the test before the check engine lamp triggered.

Unfortunately, I could never get the O2 heater monitor to complete again. Sometimes the cat monitor would lag behind. I suspect that the new catalytic converters are to blame. The computer may still be trying to get a baseline reading measurement which could take a few drive cycles. My questions are:

Could this be affecting the O2 heater test?

Does the car's computer have to adjust to the new parts before normal drive cycle tests can be performed?

Is the O2 Heater circuit controlled by a fuse?

Any help regarding this would be appreciated. Thanks and keep the pedal to the metal guys.

RPM WS6

iTrader: (3)

P0420/P0430 has nothing to do with compression or any internal engine wear/abnormalities. A bottle of "engine restore" is not a fix for this problem, it's more likely that the cats were marginal and the code simply didn't come back on that cycle, perhaps due to hotter exhaust temps on the next cycle. These codes (P0420/P0430) indicate reduced (or eliminated) oxygen storage capacity of the cat(s) and are set by comparing front O2 sensor readings to rear O2 sensor readings during a period of A/F adjustment. If the rears respond too quickly to A/F changes, then P0420/P0430 is set. Again, compression does not play a role in this.


It doesn't really sound like you've done anything so far to address the EVAP system. P0440 might be due to something as simple as a bad gas cap. There are several components to the EVAP system (purge valve, vent valve, canister, lines, etc.) Sometimes a smoke machine is needed to find small leaks, especially pinhole leaks in a line but that usually results in a P0442. Either way, you don't mention having replaced or diagnosed any components of the EVAP system so I would certainly expect this code to keep coming back.

Not sure where this thought process came from, but it's definitely not the case. There is always air in your exhaust system, the cats are not sealed and no part of any exhaust system is under vacuum (or pressure for that matter) when the engine is off - whether the cats are, or have been, removed or not. P0300 (random multiple misfire) could be caused by poor spark, poor A/F ratio, or some other internal cylinder issue (such as bent push rods, broken valve springs, etc.....but usually those more serious issues would also come with a cylinder specific misfire code - P0301 thru P0308.)

There may have been damage to the O2 sensors/wiring during cat replacement. You mentioned some rough running and P0300 immediately after leaving the exhaust shop, and it sounds as though the O2 heater test hasn't completed since that time. This test should run and complete from a cold start, but not if you leave the key in the run position (engine off) for too long before starting the engine. If you're sure you haven't done that, then perhaps there is an issue with one or more O2 sensors or wires related to them.

No. All DTCs have programmed thresholds to run and set, the PCM has no idea if new parts are installed or not. If everything is installed and working correctly, DTCs will run, complete, and either set or not set a MIL within the first complete cycle after installation. There is no "adjustment" period as far as the PCM is concerned.

Kevin Lee 487

iTrader: (1)

Just a little tidbit to add. I had a O2 heater code earlier this year. Replaced the sensor, reset the monitors and I swear it took like a week of driving 30mi+ per day for the related monitor to complete.

eseibel67

iTrader: (10)

Evap monitor does from run from driving, it runs when sitting. I do not remember exactly what it's looking for, but it checks temperature and tank pressure decay over a period of time to check for leaks. Also if I recall correctly, it requires a relatively large outside temperature swing in order for it to run.

RPM WS6

iTrader: (3)

I seem to recall EVAP monitor running during accel/decel, not idle. I've never had trouble getting this one to set when following the standard OBD drive cycle (no large ambient temp swings required.)

eseibel67

iTrader: (10)

Again, I am going off my fading memory, but I think EVAP monitor is run AFTER ignition has been turned off. I could look it up to confirm, but I'm too lazy right now.

RPM WS6

iTrader: (3)

No monitors are actively running with the ignition off.

EVAP test is in fact listed as occurring during accel/decel within the GM OBD drive cycle, and in my experience this is definitely the case.