Bluemill

For the first time in 100,000 miles and nearly 10 years, my C5 coupe 6 speed is throwing a check engine. It's PO4030, which is bank 2, efficiency of catalytic converter below standard.

Is it possible it could be bad gas? I just switched to Phillips 66, which is top tier fuel, but rare in my neck of the woods.

Any ideas on this MIL light?

Best always,

Bluemill

NukeC5

Id say it's likely the o2 sensors getting weak. Cheap and easy swap. I replaced with the NTK sensors. I made a post about it last year. They made the car run better and increased fuel economy by a little bit.

Bluemill

I went to Auto Zone to get some Techron this morning and bounced the idea of o2 sensors off of the counterman. He asked, ever replace them? I said never, not in 100,000 miles. He said seems a good possibility.

My only question on that is: Wouldn't the code come through as a bad o2 sensor instead of cat ineffiency? I took the car out last night and really beat it hard, and it ran like a champ.

My first battle with o2 sensors was on an OBD I car, ('93 Probe GT) and I fu@@ked around for 2 years of my Ford warranty before they finally replaced them. I don't think they were being dishonest, I just don't think at that time they had the diagnostics hammered out yet. Once they replaced them, the car was fine.

Bluemill

I only had time to install 1 sensor yesterday, but I did have time to crank it up to see if it cleared the MIL indicator. It did not work.

I 'll put in left side sensor today, and after doing it, clear the code with my reader. Hopefully that will do it- otherwise I have to look for some kind of after market cat. Maybe used?

The sensors are very accessible without having to drop the center pipe. You just have to get the car off the ground. Then the connectors- a little fussy, especially the one for the sensor itself, with a locking tab. I'm impressed that the plastic did not crack with "plastic fatigue", for after 14 years in a hot spot, you might expect brittle parts.

Best always,
Bluemill

martysauto

Your going to need a bank 2 cat.. The light won't go off after repairs unless you clear it or drive it long enough for the monitors to run and pass.

skip1980

Yep, put a Cat on it and be done. The PCM monitors the difference between the pre and post o2. If it doesn't see the correct change between the two then it will turn on the cel because the cat is not cleaning up the exhaust enough.

Bluemill

Yes you are probably right, but the sensors are old, and replacing them needed to be done any way- never done in 101,600 miles. The inital effect was great, for the car felt like it had been tuned up, with a new set of points and a condenser- whoops I'm dating myself.

I will reach out on the WTB and WTS pages to see if there is a racer willing to sell me his mid pipes with cats, because he put a "H" pipe on for max performance.

I wonder if top o2 sensors- upstream should be done too??

Best,
Bluemill

Cliff8928

Probably.. Most of the (4-wire) oxygen sensors only have a 100,000 mile rated lifespan. Not to say they can't last longer, but I would consider it "Regular Maintenance". I would use a good quality sensor from ACDelco, Delphi or NTK. Some people seem to have issues with Bosch oxygen sensors more than others.

NukeC5

The upstream are more important because your air fuel trims are adjusted off of them. The downstream simply read the difference through the cat. I replaced mine at 60k and noticed a difference. They bring back fuel economy And make the car more crisp in response. From what I felt anyway

3boystoys

The rear ones are only there to measure cat efficiency. The correct way to diagnose this is to check output of the O2 sensor with a scanner, even a $200 actron can graph O2 output. Unlikely your cats are toast unless you've been running a fat tune dumping a lot of raw fuel into the exhaust.

NukeC5

I agree. There would have to be something wrong to cause the cat(s) to go bad. So changing the cat(s) is not the fix. The new one(s) would go bad too if there is still something wrong that cause the stock one(s) to go bad. My old 84 Trans am still has the stock cat and just passed emissions fine. If a carbureted car can keep a cat good for 30 years these cars can definitely too.

skip1980

I still say it is a converter. If you choose to replaced the o2 sensors I would recommend using Acdelco or Denso. Denso actually makes the Delco sensor and just repackages them. Look at the Delco it will say Denso on it. Yes the front o2 are the only ones the pcm looks at for fueling and the rear are there just to see if the converter is working. If the rear o2's were bad it should set codes for lazy or slow responding o2. I used to work at GM dealerships and you would be surprised how many times cats fail.

3boystoys

I would be surprised, either way 100K miles on the O2 sensors is past when they whould have gotten replaced. If your under there bang on the cats with a rubber mallet (after it's COOL of course) and listen for any parts bouncing around. The honeycomb breaks up after a while when they fail but usually it gives itself away by clogging up the exhaust causing poor driveability or stinky a stinky smell out the tailpipe(s)

martysauto

It's certainly not a bad idea to replace 10 year old O2's, but the p0430 will stay until you replace the cat. As you said, your best bet would be a low mileage take off. Make sure the car is 100%, no fuel or misfire problems.
See below for GM's diagnostic overview. Take note, the catalyst monitor won't even run if there are other codes stored.

2000 Chevrolet Corvette V8-5.7L VIN G
Vehicle » A L L Diagnostic Trouble Codes ( DTC ) » Testing and Inspection » P Code Charts » P0430
P0430



CIRCUIT DESCRIPTION
In order to maintain a reasonably low emissions of Hydrocarbons (HC) , Carbon Monoxide (CO) , and Oxides Of Nitrogen (NOx) , the engine controls system uses a 3-way catalytic converter. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas. This reaction converts them into harmless water vapor and Carbon Dioxide. The catalyst also reduces NOx, converting it to Nitrogen. The PCM monitors this process using Bank 2 HO2S #2. Bank 2 HO2S #2, located in the exhaust stream past the 3-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalysts ability to convert exhaust emissions effectively. If the catalyst is functioning correctly, the Bank 2 HO2S #2 signal will be far less active than that produced by Bank 2 HO2S #1. This indicates that the 3-way catalytic converters oxygen storage capacity is below a threshold considered acceptable.

When the conditions for running this DTC are met, the following occurs:
The PCM captures the current rear HO2S rich/lean status.
The Air Fuel ratio transitions from rich to lean or lean to rich depending on the capture rear HO2S rich/lean status.
The Air Fuel ratio transitions a second time opposite the first Air Fuel ratio transition.
The PCM captures the response time (the time the HO2S goes from below 300 mV to above 600 mV and from 600 mV to below 300 mV ) of the front and rear Heated Oxygen sensors when the Air Fuel ratio transitions occurred.
The PCM measures the time it takes the rear HO2S voltage to cross a reference rich/lean threshold minus the time it takes the front HO2S voltage to cross the same rich/lean threshold. The time difference from the front and rear HO2S is the oxygen storage capacity of the catalyst. This DTC sets if the time exceeds a predetermined threshold.
CONDITIONS FOR RUNNING THE DTC
AIR, CKP, CMP, IAT, IC, MAF, MAP, ECT, TP, EVAP, Right Bank HO2S, Misfire, Right Bank Fuel Trim, Injector, VSS, Engine Protection, or Transmission DTCs are not set.
The engine is operating.
The ECT is greater than 75°C (167°F) .
The vehicle speed is less than 136 km/h (85 mph) .
The throttle angle is greater than 10 percent.
The engine speed is less than 4000 RPM .
The MAP is between 25 kPa (3.6 psi) and 80 kPa (11.6 psi) .
The air flow is between 14 gm/s and 40 gm/s .
The closed loop fuel control is enabled.
CONDITIONS FOR SETTING THE DTC
The PCM determines if the oxygen storage capability of the catalytic converter has degraded below a calibrated threshold.

ACTION TAKEN WHEN THE DTC SETS
The PCM illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.
CONDITIONS FOR CLEARING THE MIL/DTC
The PCM turns the malfunction indicator lamp (MIL) OFF after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A last test failed (current DTC) clears when the diagnostic runs and does not fail.
A History DTC clears after 40 consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
Use a scan tool in order to clear the MIL/DTC.
TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
Before replacing the Three Way Catalytic Converter, correct any conditions which may have damaged the catalyst.

Bluemill

I ordered the upstream sensors prior to reading your debates on this fix. There is no coolant missing from the expansion tank. The exhaust never smells like sulphur- or like low tide, no smell ever even after a WOT run.

I'm also getting no buzzing or whistling in the exhaust note. The pipe and cat casing looks very solid, it's a bronze color, not really a deep rust color. I see no signs of carbon tracks leaking out here.

I'm getting from every top wrench I know- don't jump to buy a new cat assembly.

The inside of the Z06 exhaust tips are very sooty, like black paint. Tons of carbon. One thing for sure, after doing the post cat o2 sensors, the car is a lot smoother, and more responsive.

Thanks for your help, and I'll let you know what happens after I put in the upstream sensors.

Best always,

Bluemill

92GA

My car had that code too, and it was a bad cat. I bought a magnaflow cat and installed it, but my car kept throwing a code, don't remember what that one was though. Any ways the original cat had some of the material missing inside, had a hole down one side. I bought a H pipe off a fellow off the forum, that had pretty low miles. Haven't had a problem since.

When mine was bad it would throw the code after about 10 miles of city driving, but wouldn't throw the code running down the interstate.

Bluemill

So following the lead of the thread above, I reset the code prior to my drive to work. I made a point of keeping the revs above 1500, and 2000 or more was the real target, which meant making my six speed forget about 5th and 6th gears. So I went the whole ride, 16.9 miles and 33 minutes with no coding. This was on the first key turn.

On my drive home last night, the car only got about 6.5 miles and 12 minutes before it coded. It seemed to be getting worse! Now I remembered what the old timer had said.... his car would code quickly in city driving and go a long time on the highway without lighting up. My experince was big suburb-almost city conditions.

Mmmmmmmmmm,? Carbon build up a possible issue? Is there a Lucas, or STP, or Chevron, or Shell fuel or oil additive- or intake for that matter that might break up carbon or other deposits in the converter?

I have a fairly good concentration of Techron in there right now.

I'm curious about the Magna Flow pipe that Old Timer put in. Was it the 51397 or the slightly cheaper one, like a $110 less. That number was like 98998 I think. Do you remember the code it set?

Still waiting on my upper o2 sensors from Rock Auto.

We will keep you posted.

Best always,

Bluemill

92GA

I don't remember what code it was setting after I replaced the cat. I went out to the shed, but there is no part number on the cat. I started throwing codes again in the fall of the year for the right side, so I replaced both 02 sensors again, didn't help it. I bought a used H pipe from a fellow on here that had low miles on it and haven't had a problem since. I do sometimes get a lean code after I installed my cai, if I don't let it run for a bit before I take off if it's cool out.

Boss75

A good exhaust shop can check your cats for you. Shouldn't take longer than half an hour and 50 bucks and you'll know for sure if you have a bad cat. My guess would be bad cat too...

Bluemill

Sorry Kate's not here, she busy calling her lawyer about the cloud thing releasing pictures of her....... My point though is I applied a lot of heat to the old cats today by letting it idle with the air on for 35 minutes in my driveway, then I drove it "Like I Stole It" for about another 40 minutes. It was a very hot day in New England today, 91 plus and humid, so the 35 minutes probably would have cooked whatever contaminant may have been ingested to the cats.

I found this method on this forum... by accident, when I saw the code PO430in the heading, looking for my own old thread. It sounds like a lot of people had success with this simple fix. Good chance of bad fuel contamination.

Paul, your fuel diagnosis may be right. The last full tank was from a Phillips 66 station that just changed ownership, and they dropped prices by like a dime on premium. That stuff is said to be top tier fuel, but not if it has been sitting for months because it was too pricey. Mmmmmmmm? I kind of had an inkling that may be the issue, and I put about 7 gallons of Shell and a jug of Techron when I had some space in the tank. One thing for sure, today I was likely burning a lot of that fuel after the heat up, for the entire time I was running it the revs were North of 2,000 rpm.

Too early to tell yet, but so far, no return of the MIL. That was for about an hour or so, and 4 key turns.

Tomorrow I'll put in the upstream o2 sensors, and for good measure put in some more premium- from a different, high turnover station.

Best always,

Bluemill