Scanning Catalytic Converter Operation

[peppersdog1]

fuck cats we should have stuck with lean burn technology

[mybasstruck]

can someone help me, I have a Mitsubishi eclipse 2.4l and it is throwing code p0421. they told me at Autozone that is it is 1-4 and I do not know what 1-4 means. 

[superflyjeankillbuzz]

my truck doesn't have a sensor. LOL

[hectorcriss]

thanks a lot , very helpful

[hectorcriss]

can somebody tell me how can I know which is Bank 1 sensor 1 since my car has

4 o2 sensors , I just saw the ADPTraining and it seems like is the passanger side

before catalytic converter , but I just want to make sure that is the one.

pleaseeee

[ADPTraining]

@hectorcriss Thanks for your post. OK, bank 1 corresponds to the O2 sensor on the same bank as cylinder #1. To identify Cyl-1 look at the engine, look at both cylinder heads, the head closer to the front is bank-1. Cylinder #1 is the first one corresponding to bank 1.

Then, sensor #1 means the front sensor or in front of the catalytic converter. Sensor #2 is the one after the cat. Good luck and post more...

[FarceTheory]

This computer needs to get laid!

[popchilito]

thats why i love my 94 audi, it has an upstream (pre cat) o2 sensor, i can run any cat or no cat at all and not throw a CEL

[ADPTraining]

@popchilito Good point, all pre 1996 vehicles (1994 in CA) sold in the US are OBD-2 compliant, which means a pre and post O2 sensor. The OBD-2 standard did not show up on truck until a few years later. Thanks to all.

[Sean8654]

Just had my catalytic converter replaced on my 07 Jeep, but now when the vehicle is at idle, I have an almost "burning" smell coming from the vehicle when it's at a stop. I have noticed that the muffler is pretty rusty and probably could use replacing as well and wonder if the cat and muffler aren't connected correctly. Should I invest in a new muffler/exhaust system?

[ADPTraining]

That's very interesting. Don't worry much about the muffler, unless it's clogged. Clearly it's not, otherwise your vehicle would have no power whatsoever.

These is the issue with a hot running converter and the procedure to check for possible problems:

1) Turn key ON and engine OFF. Make sure the CEL (Check Engine Light) comes ON. If not, then there might be DTC present signaling a possible A/F (Air Fuel) ratio problem (ie. Excess fuel).

[ADPTraining]

2) Hot running converter points to a rich mixture. Peek under the vehicle and see if cat is RED. If so then try not to drive the vehicle or you'll melt the converters.

3) If possible scan your vehicle and look at the FUEL-TRIMS (STFT) data parameters. If less than -10% the mixture is RICH and ECM is decreasing inj. pulse-width due to RICH condition. A/F imbalance may not by that severe, judging from your complaint (at idle only).

[ADPTraining]

3) Continued: However, an A/F imbalance will destroy the cats, if left unattended too long.

4) Final but rare possibility is a blown head gasket. Newer coolant fluids have considerable alcohol in them, making the converters give off a rotten or burnt smell. A blown head gasket is not rare. However, given the fact that you converter is new (burns very hot), the excess coolant will smell like that (on new converter).

Thanks for sharing and good luck. Mandy...

[RobertGary1]

That all true. Too many people believe that the rear O2 sensor affects AirFuel mixture. It does not, its only detecting the difference between the front O2 and rear O2 to test cat efficiency. The front O2 does affect AF mixture.

[ADPTraining]

Hello folks, actually that was true in the past. Starting around 2001, many systems also use the rear O2 as an A/F mixture indicator. Keep in mind that during warm-up, the converters are non-operational. Even after warm-up, there are instances when the converters seem as not being present. The ECM is programmed to detect these instances and take the rear O2 into account.

[davidguywilson]

If the O2 sensor were bad wouldn't it trigger an o2 code??

[ADPTraining]

Hello, OBD-2 will trigger a DTC whenever the emission levels go above 1 1/2 times FTP (Federal Test Procedure). In other words, even if the engine is running rough, the ECM may not issue a code if it detects that emissions are not high enough. That is the strange nature of OBD-2.

[RobertGary1]

The purpose of the PCM monitoring the O2 sensors for SMOG is ony to determine if the sensors are returning results in a realistic range. So you will generate a code if the voltage is out of a reasonable range. If the O2 sensor is slightly off the PCM will believe it and adjust AF accordingly. Rear O2's are usually heated and the resistance of the heater is also tested to ensure its working.

[ADPTraining]

Very good, adding to that: The O2 sensor detects only Oxygen content. The ECM deduces that the higher the O2, the leaner the mix and vice-versa. ECM looks for 0.15 to 0.8 volts sine wave at at least one Hertz or one cycle per second for the front O2 or for the rear O2 if vehicle equipped with LOC/Baby converters. On todays' systems all O2 sensors are heated.

[ADPTraining]

However, all O2 sensors are now being replaced on newer models with AFR air-fuel-ratio or wide band sensors. These are not regular O2 (Zirconium) sensors and have a much wider range of detection of A/F ratio.

AFR sensors also do not output a voltage. These are current devices, which output a small current inversely proportional to mixture in the Milli-Amp range. Good luck to all.