Finally resolved the H2's worsening engine warning codes.

Codes History

• Weekly occurrences of "P0420 Powertrain Catalyst System Efficiency Below Threshold (Bank1)"
• Progressively worsened over a period of months, eventually occurring every few days, then every trip then all the time.
• Over the months an additional code "P0300 Powertrain Random/Multiple Cylinder Misfire Detected" started to occur at high revs (4000+)
• Again this worsened occurring every time revs were high and then all the time.
• Other codes occurring were "P0172 Powertrain System Too Rich (Bank 1)" and "P0101 - Powertrain Mass or Volume Airflow Circuit Range/Performance Problem"
• Engine performance deteriorated, hills were difficult, revs needed to be higher than normal and eventually the car was undriveable.

To summarize the codes were P0420, P0300, P0172 and P0101

Work done

• Air-filter changed
• Spark plugs changed
• SP wires changed.

All these changes made no difference.

Final Fix

• CUT both CATs off, on examination bank 1 was just like a bucket of sand, well plugged and damaged (see pic) bank 2 looked OK.
• Welded in 2-off Maganaflow Universal CATs and replaced all Lambda (O2) sensors

Conclusion and results
Obviously the CAT was starting to deteriorate, the more it degraded the worse the exhaust gas flow and the hotter it got and the more it deteriorated leading to its eventual collapse ... like a chain reaction. Its also worth noting is that the O2 sensor on the engine-side of this CAT was almost welded-in and hard to remove suggesting extreme heat, also this sensor is in an inaccessible place and hard to remove but has to come out 1st in order to access the exhaust-pipe retaining nuts.

So now the H2 is back to normal, sounds great, no codes, better fuel economy, more power!!

So feel free to ask questions, I'll do my best to provide pictures/details on this experience for anyone who has similar problems and concerns etc

 

I'm curious about a few things since you run LPG.
How many clicks did you have on the H2 before you got the conversion & after? Total mileage/km?
How much did the fuel economy increase?


I bet you're happy the problem is over. I will keep this in the back of my mind, in case I ever run into something similar.
Thanks for posting the solution!

 

OK.

The LPG conversion was done at 35000 miles/56000 Kilometers, the current mileage is 64000 miles / 103000 Kilometers.

The fuel economy is a tricky calculation with US gallons, UK Gallons, Liters and fuel prices (which vary) all in the mix, also there is some gasoline usage whilst the engine warms up and switches over to LPG.

Anyway here in the UK it roughly doubles the economy or halves the fuel cost whichever way you look at it.

Yes very relieved and happy

 

I'm really scratching my head about why the CAT has so much "soot" in there. My old 03' H2 had around 120k miles / 193k km & that was never an issue. I've never run into a vehicle that needed a new cat anywhere even near 100k miles / 200k km.

LPG is clean burning, so it's obviously not that.
Hopefully, it was a faulty CAT & the new one won't need to be changed for a very, very long time.

 

Difficult to say what the root cause was. Apparently there was a warranty issue with some H2 CATs and I know at least 1 other person here in the UK who had the same problem (not sure on mileage)

There are a few threads around describing H2's with similar issues which is where I took my lead from.

Having looked into CAT technology they do seem prone to damage, things like road speed-bumps, oil contamination, tapping them to check for rattles, not running them in properly but I'm no expert and there's a lot of chatter out there.

Eastern Catalytic have some good videos on the subject.

 

thanks for posting your findings and the solution! no cats on mine but good to know for other vehicles as well.

steve