2003 Corolla cat converter

Let me know, snipped-for-privacy@gmail.com what you find. I too, have a 2002 Toyota Corolla and might need to replace the cat convertor. The dealer wants $1700. I know some after market ones run as low as $200...

I smell a rip-off. First, I've never heard of a warning light of any sort being connected to a catalytic converter. Why would there be? Catalysts don't fail catastrophically or damage the engine when they wear out; they just gradually stop contolling the engine's emissions effectively. And the engine doesn't care how clean or dirty its exhaust is.

Second, it's possible that the grid inside an old catalytic converter might collapse and cause a blockage resulting in exhaust backpressure, which is entirely possible on a car with 113K miles on it. But you said you're getting great mileage. You also said that you only notice a slight loss of power, and only notice it occasionally.

A blockage in the exhaust system would likely create enough back- pressure to cause a significant power loss, one that would be noticeable full-time. And it would get worse as time went by and the grid continued to fall apart inside the housing. The same would apply to your gas mileage: not only would the engine run less efficiently with increased backpressure, but additionally, you'd press harder on the the accelerator in order to get a given amount of power out of the engine. Both would be detrimental to your fuel economy.

Third, catalytic converters don't cost a thousand bucks. I had the one on my Accord replaced at cost about ten years ago, and it was only one or two hundred bucks. Dealer markup and ten years' worth of inflation don't amount to a thousand dollars just for the part.

And this guy claims he's having trouble finding a common, consumable part for one of the best-selling cars in the U.S.?

Yumping yenitals. Grab your wallet and run.

Geoff

Doesn't the oxygen sensor located after the catalytic converter start putting out a big signal when the converter fails?

The OBD II (required in all vehicles sold in the U,S. since 1996) system will set a DTC and MIL if the catalyst is not doing its job. The engine may not care how clean or dirty its exhaust is, but the EPA kind of does and so the OBD II system monitors catalyst efficiency.

Catalytic converters can fail for reasons other than blockage, like having the catalyst coated with contaminants.

Whether this diagnosis sounds right or wrong depends on the diagnostic trouble code and whether your mechanic checked the systems related to catalyst performance.

I hadn't considered OBD II because I've never owned a car that had it.

What's a DTC and a MIL? Are you saying that because of OBD II, the Check Engine light _will_ come on if the catalyst stops working? Or would OBD II just retain an error code to spit out the next time the car goes in for service?

Well, sure. But my point was that the catalyst's merely failing to catalyze wouldn't affect engine operation (hence my "the engine doesn't care" remark), while a blockage inside the catalytic converter's housing might.

Geoff

The O2 sensor located after the catalytic converter puts out a signal (not big) all the time. If the signal from the O2 sensor indicates that the cat is not doing its job then the electronic control unit (ECU) will turn on the malfunction indicator light (MIL).

OBD II: On Board Diagnosis generation II DTC: Diagnostic Trouble Code MIL: Malfunction Indicator Light (the proper term for what is commonly called a check engine light) ECU: Electronic Control Unit (commonly referred to as a computer or black box even though it is silver)

An OBD II system has 2 O2 sensors for each bank of cylinders. O2 sensor #1 is in the raw exaust stream and provides feedback to the ECU when the system is in closed-loop mode so the ECU can adjust the air/fuel mixture. O2 sensor #2 measures the exhaust coming out of the catalytic converter so the ECU knows if the converter has done its job or not. In other words, the exhaust measured by sensor #2 should be cleaner than the exhaust measured by sensor #1. If not, then the converter is bad.

Some parameters need 2-trip detection logic before the ECU turns on the MIL. In other words, it has to go thorugh 2 operating cycles defined as a trip (engine fully warmed up, catalyst warmed up, O2 sensors warmed up to operating temp, a certain distances travelled) before it turns on the MIL. If 2 more trips are detected without the condition that turned on the MIL, then the MIL is extinguished but the DTC is retained in its memory until it is cleared.

While this is technically true, it is a little misleading. Although the engine will not care if the catalytic converter is working as long as the exhaust is not blocked, the ECU does care and will illuminate the MIL if the converter's efficiency falls below a certain threshold.

But how does the ECU know, from the second O2 sensor's signal, that the converter isn't doing its job?

The OBD II system compares the oxygen level signals of the 02 sensors in front of and downstream of the catalytic converter. If the downstream 02 sensor signal becomes very close to or the same as the upstream 02 sensor,it means the converter is not working properly. This indicates that the converter is not removing all of the pollutants it is designed to remove. When the OBD II system compares the two signals, it will show a (MIL) if the two signals are not within spec.

Good explanation.

More information about this-- the mechanic (and I on my own) found cat converters for about 1100 from dealers only. I did find one online that lists for 1100 but sells for 341. The mechanic told me that he would reset the light and recomended I do an injector clean and oil treatment.

The #2 sensor was replaced several months ago after I took it in with the check engine light on. A little while after replacing, the light came on again and he reset it for me saying that the systems are very sensitive nowadays and that I shouldn't worry about it.

My biggest issue is whether it will pass emissions inspection this Saturday.

Paul

If It were my vehicle I would take it to a competent technical and have it properly analyzed to determine the problem, that is activating the light and frying the sensor, and have it corrected. ;)

mike hunt

properly analyzed to determine the problem,

Ya, for some reason your mechanic seems to be just shooting from the hip so to speak. Then again I doubt he wrote "that I shouldn't worry about it." on a invoice.

You are correct on the invoice. After talking to the inspection folks they tell me that I need to "reset the OBD". They provide a driving sequence that 'should' reset the OBD. According to them the car must be driven through its "drive cycle" after any DTC's have been erased from the PCM's memory. Blah blah blah, I just need for my care to pass inspection..........

Danny G. wrote:

properly analyzed to determine the problem,