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This 2005 Chevy G3500 van with a 6.0L engine has me baffled. It has a recurring PO430 code. We replaced both left and right converters and all 4 oxygen sensors and yet, PO430 keeps coming back. What am I missing. No other issues with the driveability with the vehicle. Is very frustrating. What am I missing? By the way, PO430 applies to the right bank, correct?

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There is a TSB for a ground issue that can cause that code. Go to TSB's and search for p0430.

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What brand of sensors and cats? Did you use OEM?

Any small exhaust leak can affect efficiency monitoring. They can be so small you may not hear them without a stethescope. You can also smoke the exhaust and check for leaks that way.

As I do a lot of work for other shops, I've seen people mix up bank one and bank two, A LOT. If I'm not mistaken, Bank two is on the passenger side, BUT the exhaust crosses itself just before the cats, so the cat for bank two is actually on the left.

Most of the recurring efficiency codes I get from other shops are either a very small leak, a poor aftermarket cat, or they changed the wrong one.

ricmorin wrote:What brand of sensors and cats? Did you use OEM?

Ah yes. The brand debate. The only aftermarket exhaust brand I use is Walker. I do at times use OEM but due to cost on this one I used Walker for both of them. The brand of O2 Sensors was Nippendenso which, according to advertising is the manufacturer for the OEM. Now, I know, there are shops that will use only OEM because according to them, they have had issues with aftermarket brands. There are times, as mentioned earlier that I use OEM but not always. So far, in 21 years of business, I have not had an issue with Walker exhaust or Nippendenso O2 Sensors. I felt comfortable using them. The interesting thing I discovered is that when I connect my lab scope to the B1S2 sensor, I get a flat line at about .8v. This would be the post cat sensor for the pipe going into the muffler on the right side which originates from the left (drivers side) bank of the engine. The question I have answered is which sensor does PO430 apply to? If I unhook the B1S2 sensor with the engine running I get no code suggesting I may have a PCM issue.

The post cat O2 sensors are responsible for monitoring efficiency. 800mV sounds rather high even though the scope shows a flat line. Is the other O2 at 800mV also? Usually they will stay between 400 and 600 mV.

I've pretty good success with ND sensors too. The only time I had trouble was with a GM product. Still using them today.

I won't use Walker cats. There's a reason why they are half the price of an OE cat. In fact, I've had the local Walker rep here several times in the last few months for major fitment problems. Walker used to be a giant in the business and quality was superb. Lately I've seen it slipping away. I've replaced at least a dozen aftermarket cats for efficiency issues; never had a bad OE cat. They fit and they work.

If the other O2 is lower than the suspect one, you may just have a bad sensor. The trims are ok on the affected bank, yes?

Have a lot of issues with worn or overdue spark plugs causing cat codes. Ive not seen plugs mentioned in this thread.

jbadenoch wrote:Have a lot of issues with worn or overdue spark plugs causing cat codes. Ive not seen plugs mentioned in this thread.

Well, well, the thought of worn plugs causing a cat efficiency code and not set a lean or rich code from the upstream sensors is a new wrinkle to ponder. I aint making fun or knocking it, just trying to understand the logic of it.

This vehicle has had all 4 O2 sensors replaced twice an this code PO430 keeps coming back. Not consistently. For example, this van went the whole way from PA to Texas with no problem. The owner gets home and the first run he makes the CEL comes on an we got a PO430. Strange. Ricmorin mentioned fuel trim numbers. Short term is +1 for both banks and long term is +5 for both banks. The one bank, the post cat sensor is operating fine but the other one is a flat line at .75-.80v. Does not change regardless how the van is driven.

Have had a few where exhaust manifold bolts had broke and would suck air causing like issues.

On GM's of that era, I believe the PCM sends out a bias voltage to the sensors. Also, you can view the heater currents on a scanner, which is important during warmup.