'03 LE - P0420 Code

[cny03owner]

I've owned my '03 Corolla since it was brand new, and in the 6 years I've had it I've racked up 110k miles on it, with few problems other than the basic maintenance -- oil changes, filter changes, tires, brakes, etc. About 6 months ago, the check engine light started coming on intermittently, and stayed lit constantly starting about a month ago. The dealer read the code, indicating that it was a P0420 code, and stated that the catalytic converter needed to be replaced, along with an assortment of gaskets, oxygen sensors, and assorted hardware -- with repairs totaling around $1700.

I've done some research online about this problem, and noted that there are a wide range of suggestions on the repairs, but most indicate that the catalytic converter should be replaced (primarily from a anti-pollution standpoint, not a performance standpoint). The car will not pass an upcoming NY State Inspection, as long as the check engine light is on.

In the last year, I've put about $2000 into the car for 2 wheel bearings, tires, front brakes, and some other minor repairs, and another $1500 into body work from a minor fender-bender. Add in the latest repair estimate, and I'm getting relatively close to what the car is worth as a trade-in, and that's assuming that nothing else goes wrong in the near future. So at this point, I'm asking myself if I should do the repairs, or if I should cut my losses, and start hunting for a new vehicle.

If not for the inspection issue, I'd likely continue driving it without replacing the catalytic converter, as it runs great and it's paid for -- and I consider the car just broken in (a previous Corolla I owned made it to 182k before the rust did it in). I anticipated getting another 2-4 years out of it, before relegating it to winter rat/second car status. The body is clean, no rust, and other than losing a little oil between changes (down 1/2 quart at the last oil change), something I'd expect at that mileage, the car is reliable transportation for me.

Anyone have some advice or thoughts on this for me? Thanks in advance.

[holler1]

My daughter's car (03 Corolla 92500 mi) just had the same code last week. With advice from some people on this forum 2003 Corolla maintenance at 90K?
I replaced the rear oxygen sensor and so far the code hasn't returned, although it has only been driven about 100 miles since. The oxygen sensor is much cheaper than a cat converter so I would try that first. It is easy to change from underneath the car on the passenger side. The electrical lead goes through the floor under the left side of the passenger side mat and connects behind the center console.

[cny03owner]

Thanks for the reply. Got the same advice from a couple other folks I know that are mechanically inclined. Definitely disappointed with the dealer at this point for trying to sell something that might not be needed.

Update at this point is that the check engine light hasn't come back on since the dealer reset it, and the car passed the state inspection the other day. I'm keeping my fingers crossed, and will see what happens. If the light comes back on, I'll definitely try replacing the rear oxygen sensor and see what happens.

[holler1]

Update- code P0420 came back on my daughter's car after I replaced the rear O2 sensor.

[new echo owner]

It has been the general assumption that the rear O2 cause P0420 to set, but that isn't exactly true. It is only one of the possible cause that sets P0420. A bad Pre-Cat A/f or O2 sensor can cause P0420 to set to, that is besides the Cat itself. Even internal engine problem can sometimes cause a false P0420.

N.E.O.

[rwd_3tc]

the problem may be the ECM. i just checked for any TSB or bulletin's on ETAS

[holler1]

I think I'll replace the front A/F/O2 sensor and see how if that helps. I was planning to do that anyway but could not find an OEM O2 sensor locally, have to order one.
NEO- What other kinds of engine problems might trigger a P0420? The first time this code came up there as also a P0442 but that hasn't come back.
rwd_3tc - I saw another thread mentioning ECM and P0420 but could find no details. Did you find anything?

[new echo owner]

Injector leak, exhaust leak, and even a A/F sensor that is not functioning properly can cause a false P0420 code.

There was a TSB for P0420 back in 2004, do a Google search for 'EG028-04', however, your car may already have that performed.

N.E.O.

[holler1]

I checked real-time data on my daughter's Corolla with a code reader with the engine running, and both O2 sensors outputs are varying between .05 and a max of.6 to .7 volts. The front sensor reads a little higher (.7) than the rear (.6) but my understanding is that the max voltage on the rear sensor should be a lot lower, meaning the cat converter is really not doing much. Am I interpreting this right?

[boopie]

had the same problem on my 03 S. Luckily i had only 79,500 miles on my car when I took it to the dealer where they replaced the cat and reprogrammed the ECM and fixed the check engine light. It was still under the 80k warranty so i didn't have to pay. My advice is to get the cat replaced. Light will keep coming back if you don't. Oh and get the ECM fixed too by the dealer. THat they will do at unlimited mileage.

[new echo owner]

Originally Posted by holler1

I checked real-time data on my daughter's Corolla with a code reader with the engine running, and both O2 sensors outputs are varying between .05 and a max of.6 to .7 volts. The front sensor reads a little higher (.7) than the rear (.6) but my understanding is that the max voltage on the rear sensor should be a lot lower, meaning the cat converter is really not doing much. Am I interpreting this right?

How did you obtain those readings? Was the engine at idle when you record those reads? Do you have an infrared temp gun?

N.E.O.

[holler1]

I just got a new INNOVA Equus 3140 scan tool that let's me see real time data from the engine. A Christmas indulgence. This was after warmup. The scan tool reads the coolant temp (~190). At idle both sensors read low, going in a cycle from about .035 to .055 volts. I ran the engine up to about 1500 rpm and that's where I got those readings above. Last night, I found an 04 shop manual on *************.com and the "real" test shown there for code P0420 is run at 2500 rpm. Some of the folks on this forum might want to access that manual; it is very detailed.

I replaced the front O2 sensor today (Denso) and will check the voltages again if I get time and see if the code comes back.

I realize some other conditions may cause the code, but the tests from the manual don't say how to check for those, other than visual checking for leaks.

[new echo owner]

You do need to check the O2 readings with the engine around 2500 to 3000 rpm. In general, sensor 1 reading will be fairly active, and sensor 2 would be cycling at a very slow rate comparing to sensor 1.

Also if you have a infrared temp gun, check the inlet and outlet temp of the cat around 2500 rpm. Should at least have 100 degree F higher at the outlet, which would indicate there is 'secondary combustion' in the cat.

What other things do you have to check?

N.E.O.

[holler1]

NEO
I'll try the check at 2500-3000 rpm. However I don't have an infrared gun so can't check temps. I apparently misunderstood how the rear O2 sensor should read. I thought it was supposed to read a lower voltage, but you're saying it is a slower change. I'll look for that. If the infrared gun is relatively cheap I might be able to get one tomorrow. My daughter is leaving on Friday so I won't have access to the car after that. I'm giving her my old code reader so at least she can check to see what codes come up if the CEL comes back.

The main thing I would like to do is find out if the cat is bad. You had mentioned several other possible causes; exhaust leak, injector leak.

[new echo owner]

Since you have a scan tool that is capable of reading live data, that will help tremendously in determining if there are other things that is causing the P0420. Monitoring the long and short term fuel trims, if that is available will help in determining if the fuel system itself is out of range. The MAF readings would help too.

As far as, exhaust leak, that is simply a check for cracks or the telltale black soot around the exhaust system before the cat, and listen for exhaust noise at idle and off idle.

N.E.O.