bandit67

My recently acquired 05 is popping the 420 cel code every few days now. In scanning the net for some trouble shooting tips I have learned that many things can cause this code. As I understand it, the ecm is seeing either a large or not large enough reading by the fore and after O2 sensors. Causes can be, from burning too much oil, coolant leaking into cylinder, clogged cat converter, bad sensors, bad gas, 'dirty" converter, and other conditions. Heard horror stories of folks replacing EVERYTHING......some even twice and not stopping its resetting. Scotty on U tube says run a gallon of lacquer thinner in a half tank of gas and clean up the converter can solve the problem. I prefer to troubleshoot first before I start to replace parts when possible. O2 sensors first. I did a scan last nite while the car was running and system was at normal operating temp. Both sensors were constantly moving from as low as .079 to as much as .856 at idle. Trouble shooters say that if one locks in at like 1. something , it is for sure bad. Mine seems to be on the correct working parameters.
The car has 202k miles and the PO said the head gasket had been replaced. I usually drive about an hour to work in the morning ........no code. And if the temp stays low.....no code driving home late in the day. But, now that temps in the afternoons are warming up....code sets on the way home.
I have not driven the car long enough to see any oil consumption. I changed the oil at first with the listed 5-20 wt non synthetic. Not sure what the PO was using. If the problem is being caused by oil consumption......changing in new converters prolly will not be the quick fix. One guys problem did not get fixed until he found a shop that put in a California emissions converter even though his car was NOT a California car. Anyone with any luck in solving this code on your car.........

bbarbulo

it sounds like the code is intermittent, so keep the scanner plugged in on the way home when you normally see the code come up and watch the live readings.

also, most scanners have a feature where it will give you the snapshot of all the sensor readings at the time the code was set. the ECU saves this info for troubleshooting purposes, so your scanner should be able to read this data. See what the primary O2 and secondary O2 sensors were saying at that time.

bandit67

Thanks bb, I have never done that......tried with my scanner to catch a code as it popped. What might I see...........a close reading or wide. Which sensor is primary......the last one catching the 'work' of the final cat.

bbarbulo

so on the scanner, it's called 'freeze frame data' - that is what the computer is reading at the moment the code is triggered. it captures all the sensor readings at the instant in time. if your scanner can pull it up, it should tell you what the PO2 and SO2 were reading.

if i remember correctly, P0420 is the catalytic converter efficiency below threshold code - meaning that the primary and secondary O2 readings are close to each other. primary is the 1st O2 closest to the engine, secondary is the O2 after the catalytic converter. the controls theory here is that the engine puts out whatever it puts out, so the primary O2 is the baseline reading. then the cat 'scrubs' (chemically) the exhaust so in theory the secondary O2 should be a reading significantly different from the primary O2. so when the two readings are close to each other, that (in theory) means the cat is no longer able to effectively 'scrub' the exhaust.

now, I absolutely despise aftermarket catalytic converters. and the sale of used OEM converters is illegal. so the law forces my hand in this matter... I think (while great for the price), that aftermarket cats are abominations. the biggest mistake one can make is to incorrectly diagnose a 'bad cat' and mistakenly replace an OK OEM cat with an aftermarket one. then you're gonna be replacing them every couple of years b/c the aftermarket ones CANNOT last nearly as long as OEM ones. OEM ones are made with precious metals, aftermarket ones is ceramics basically. I would attempt to incinerate the debris from an OEM cat to effectively clean it. Or chemically strip the carbon deposits... or anything to prolong the life of it. By definition, catalyst means it isn't consumed, so in theory a catalytic converter should last forever. What happens is carbon buildup blocks the catalyst from touching the gasses and then the catalyst is ineffective. also catalysts are high temp metals... like beyond anything your engine can generate (and still survive). Your engine will melt before the platinum, rhondium, palladium, etc... in the catalytic converter even heat up. Platinum for example melts at over 3200 degrees F. In the foundry, we cast engine blocks at around 1400F - pure aluminum melts around 700C (1300F).

Failing that, I have found that providing a small injection of fresh air to the secondary O2 will keep it happy. So I have previously used spark plug non foulers with a tiny hole drilled into the side, and that was enough to make the ECU happy.

bandit67

thanks again , bb, great info. Now I understand how that system is SUPPOSED to work.....and now to determine what is causing the code to set. Obviously, the voltage being returned to the ECU is staying to close to the parameters for too long a time and that causes the code to set. Since it is not locked in trouble at all times, and the O2 sensors are moving quite abit, I am pretty sure they are not defective and needing to be replaced., I am leaning to a 'dirty ' cat. So, the suggestion made to run a gallon of lacquer thinner at a half fuel tank is an attempt to burn some of the carbon clogging or prevent the cats from performing effective scrubbing of the exhaust. I agree completely with your opinions on aftermarket cats......avoid them if possible. Based on the high temp metals that the OEM cats are made from , it would seem that just about any chemical used in an cleaning attempt would not damage the function of the cat when done., is that correct. I may try a few things prior to using the non fouler option just yet.

bbarbulo

I haven't tried lacquer thinner in the gas... I've heard of it before, but never needed to do it. If I was in the situation, yeah, I'd prob try it. But I would be replacing the engine oil immediately after, any washdown from that treatment would badly contaminate the engine oil. so replacing it immediately would be imperative.

My thought was more removing the catalytic converter and soaking it in increasingly harsh chemicals.... soapy water, simple green, alcohol, mineral spirits, etc... until the desired result was achieved. but try the easy way first - do your due diligence though; I have't tried it. But I would research first what the theory behind it is, and if lacquer thinner would affect seals, fuel pump, injectors, and any coatings that may be present on the pistons. I wonder if gas-line antifreeze would have the same effect (ISO HEET or whatever they call it)

TailZ

My GF Infiniti I35 had this problem.. P0420 would pop up every 80-100 miles or so. Tried fuel additives = waste of money. Decided to just buy the spark plug non foulers and hook it up to her downstream o2 sensor and call it a day. Code no longer pops up and just passed smog here in CA.

bandit67

Ok , after listening to several vids saying the lacquer thinner in the gas tank trick was unsuccessful in burning off the crud that may be responsible for causing the converter not to be efficient enough to stop the PO420 code, I went with a non fouler and after three days , no code has popped. Will continue to monitor.......thanks all......