oldanteek

OK, I could really use some expert advice on my issue. I've read many previous posts, but I am still scratching my head on this one. I have the VSC, VSC off and check engine light on over and over. I have replaced oxygen sensors, had it smoked and replaced the rear cat with a universal and still the lights come on with P0420 bank 1. What to do? How do I know I replaced the correct cat? Could bank 1 be the #1 spark plug and I should have replaced the front cat on this unit? Please help. Thanks!!

GEORGE_JET

Here is a write on this code that explains the steps to troubleshooting this code. It should help you out.

oldanteek

OK, so we replaced the front two O2 sensors and the rear one was deemeed good by the dealer. We replaced the rear cat with a universal, as the walker after market didn't fit (CA emmissions?) After installing the universal the VSC, VSC off and check engine came on with days. We then replaced the mass air flow sensor and the lights came back on within days pulling the P0420 code again. The dealer smoke tested and did all the diagnostics with nothing found. They now say the rear universal is too small for the car and I need to put a OE cat back on the vehicle.

I did go to Auto Zone and used their OBD II tool and cleared the codes. Within 10 minutes, the VSC and VSC off lights came on (no check engine light came on) and when we got home and stopped the car and then restarted the lights were off. We then used the vehicle this morning to work and the lights were still off. Does the code have to hit 3 times before the check engine light comes on?

What can I do at this point...PLEASE HELP!!!!

GEORGE_JET

I suspect that the source of the issue is further upstream. The ECM is alternating the mixture between rich and lean, and then monitoring the downstream O2 sensor, it expects that the cat will use the excess O2 to oxidize the byproducts from the rich mixture.
Do you have access to a scanner that will show you what the fuel trims are? Both short and long term fuel trim? Since this code is for bank 1, you want to compare these numbers with bank 2. A leaky or partially clogged injector will throw the numbers off (make sure to note if the numbers are neg, or pos).
Once you have determined that the fuel trim is acceptable, I would want to look at the patterns on a o'scope. You can pick up a basic scope off ebay for less than $100, you want to be able to verify that the patterns off the upstream O2 sensors are switching properly. Once again, use bank 1 as a reference.

I feel that you have to verify that the engine is running correctly, first by checking the fuel trims, next by checking the O2 signals. I think that the fuel trims alone will point to a problem.

Ps the ECM is designed to adj the fuel trims to optimize running, so it can adj the trims to considerably large numbers. The ECM is not programed to see this as a problem, so it does not turn on the check engine light for this.

oldanteek

I had the dealer check the fuel trims and they were -2 to -3 and the acceptable range from dealer was -1 to +1.

The short was -2 and the long was -3.

GEORGE_JET

Both banks were only 2~3 %? I am surprised that they are that close, that would indicate that the engine was running very close to ideal. Odd. The next thing I would suggest is trying to get a hold of a o'scope and checking the signals from the O2 sensors, comparing signals from both banks, paying close attention to amplitude (although if the fuel trims for both banks are very close to the same, it would indicate that the signals should be the same).

Has any other work been done to the engine in the last several months? ESPECIALLY around the intake, air induction? That is before this problem first showed up?

oldanteek

OK let me say I am not a mechanic, but trying to be an educated consumer and get this fixed once and for all. I asked the dealer to tell me my fuel trim readngs and they came back with -2 to -3%. I did't ask if this was bank 1 or a combination reading from bank 1 and bank 2. I take it each bank will have their own readings both short and long term? From what I'm being told -2 to -3% really isn't that bad and this doesn't gave any clue based upon those readings.

If you need better numbers on the fuel trim, what should I ask for? A fuel trim reading for bank 1 and one for bank 2?

We did get a knock sensor code and replaced the two knock sensors. They had to take the intake manifold a part to replace them.

GEORGE_JET

The fuel trim will have separate numbers for each bank, and as far as 2 or 3% is not much, certainly not enough to indicate a problem. But are both bank trim numbers close to each other? (again a couple % would not be a major issue). If one of the banks was in the double digits, ie 14 ~20, then yes that would certainly be cause to look further.

Now the knock sensors in themselves, could not cause this problem, BUT as you are aware, they had to remove the intake, as this could be part of the problem for two reasons. First and most obvious, if there was a leak which could affect only one, or cylinders. Second and worse, some gasket dressings, ie such as most RTV's can destroy a O2 sensor. When working on the intake manifold one must be aware of what chemicals are being used, and what their impact will be. Not all mechaincs are aware of this.

Now if this were my car, I would be checking the O2 signals with a o'scope. But most mechanics do not have access to a scope, or would even know how to use on. Although I have ase certs, 1 for advanced engine diagnostics, my background is repairing computer controlled equipment for the production of computer chips.

You state that you replaced the O2 sensors, was that all three, or just two? At the minimum I would suggest that the O2 sensor after the main cat be replace, (once after verifying that both bank1, 1 and bank 2,1 O2 sensors are switching properly. After that point I would recomend changing out the cat again. Do you know if the universal cat they replaced was a 3way cat?

oldanteek

When they replaced the knock engine sensors, they initially didn't replace the gaskets and used the old ones. My foreign car mechanic discovered the leak and had me bring it back to the dealer. They replaced the gaskets, but I could still smell anti-freeze, so they power washed everything off in case of residual anti-freeze.

The lexus dealer only replaced the front 2 sensors and not the back. The last time I had it in for diagnosis, they checked the rear O2 and said it's fine.

GEORGE_JET

Interesting, I wonder what the fuel trims were before they replaced the front two O2 sensors. The trim numbers are very low, which appears that the engine is running well. But the fact that the rear O2 sensor has not been replaced concerns me. How many miles do you have on the car? I have not worked a lot with the AF sensors, but I have worked a lot with the older style O2 sensors. The basic operation of them can be compared to a battery, and they have the same finite lifespan. The elements that generate the voltage (inside the O2 sensor) on top of a finite lifespan, are also easily contaminated, on top of that, there is a heater inside of it. As you can imagine, the heater also has a finite lifespan.

The computer uses the rear O2 sensor (the one behind the main cat) to determine if the cat is working correctly and normally the O2 sensor should fail before the cat. But there is one large cavet there, and that is the fact that you had the issue with the knock sensor, coolant leak. Did you notice any smoke after they replaced the knock sensor? How long ago did you have the coolant leak? It is starting to sound like they could possibly have caused this problem.

One thing is confusing me, you state that a universal cat was installed. A Dealer installed this? Not that I have a issue with aftermarket (my issue is more with dealers, I used to work for a chrysler dealer, and I know some of the cr@* they pull. I get major tweeked that they are now looking for a bailout after all the stunts they pull.

oldanteek

It's probably been 3 or so months since the knock sensors were replaced. I actually found out about the leak from my foreign car mechanic who discovered it and told me to bring it back. I did smell anti-freeze, but no smoke. No clue what the trim numbers were before the leak.

I think what I really need to do is try and collect all of my paperwork and get you a full picture of the sequence of events up to this point. The vehicle has 130K on it and yes it runs wonderful! I do need to check gas milage and see where we stand. I thought it was getting good milage, but wife thinks it maybe going through gas as of recent.

The universal cat was installed by my foreign car mechanic. He tried to get a after market Walker, but when he tried to install it didn't fit. I don't know if it was CA emmissions (which I have) or what, but the correct Walker part # didn't work, so I opted for universal. (regreting now) It wasn't even days after the light came on and they said the mass airflow needed replacement and then a few days after the P0420 came on again and here we are...

If I knew replacng the cat withan OE would solve the issue, I may possibly do it, but I am not convinced that it's the cat. I have good power and acceleration.

GEORGE_JET

The universal cat wasinstalledby my foreign car mechanic.He tried to get a after market Walker, but when he tried to install it didn't fit. I don'tknow if it was CA emmissions (which I have) or what, but the correct Walker part # didn't work, so I opted for universal. (regreting now) It wasn't even days after the light came on and they said the mass airflow needed replacement and then a few days after the P0420 came on again and here we are...


I assume that the check engine light originally came on, before the cat was first replaced, was the code then P0420? But why did they clean the mass airflow? The rear O2 sensor has never been replaced?

ivory98es3

iTrader: (1)

I have gone through this code before (search for it). It is a Pain In The @$$!! It started for me by having to replace the flex pipe section of my exhaust due to a leak. Well toyota wanted $1200 for the pipe because it is integrated with the CAT. I told my mechanic if there was an aftermarket he could get for less. He came back with one for $650. SOLD!! He installed it, checked for leaks, found nothing and I drove off. About 15 days later, I get a CEL for code P0420. I had everything checked, A/F sensors on bank 1 & 2, the O2 sensor after the new CAT - All were good and working perfectly. What it comes down to is that the ECM's on these cars have such "tight" tolerances that anything but OEM parts are gonna cause the P0420 code. I went to a testing station for car inspections, I asked them to put the sniffer in the tailpipe and give me a reading - everything was in normal ranges for emissions. I found a work around by installing a diode inline w/ my O2 sensor faking out the ECM - I have been CEL free for almost 25 months now. I know it's the best solution but it works for me.

oldanteek

Do you have a part list and instructions on how to perform this work around.

GEORGE_JET

I would be interested in the work around too, if you don't mind.