04 S60 - p0420 - catalytic converter

[ionianp2]

Hi Everyone,

I hope all is well. I will get straight to the point. Had a p0420 code the other day, ie cat runs below efficiency threshold. Car runs fine. No increase in engine temp nor signs of backpressure. I reset the code drove at least another 100 miles and it hasn't come back yet.

I used a scan tool with graphing capabilities and checked the downstream O2 sensor B1O2S2 and it does oscillate rapidly. The wideband (upper) sensor (which measures in milli amps) oscillates as well and the short term and long term fuel trims seem to be near zero ( less than 5%).

In other words I think the engine should be in good shape. No vacuum leaks are noticeable from the engine bay. However the downstream O2 sensor seems to show that the cat is not doing its job.

New OEM cats are extremely expensive. Has anyone had any good luck with aftermarket? If so, what brand?

It's a shame that this had to happen. The car has 147k miles but I've read that cats can go for much longer.

Any input is appreciated.

-Ionian

[RickHaleParker]

P0420 does not mean the catalytic converter is defective. It means the cat is not cleaning up as well as it should. This could be due to a lot of things that mess up the Air/Fuel ratio. It rarely is a defective catalytic converter.

ECM-4801 ( P0420 ) Three-way catalytic converter (TWC) efficiency.

Condition
The control module continuously checks three-way catalytic converter (TWC) efficiency by comparing signals from the rear heated oxygen sensor (HO2S) with the front heated oxygen sensor (HO2S). Diagnostic trouble code (DTC) ECM-4801 will be stored if the efficiency of the three-way catalytic converter (TWC) deviates too much.

Substitute value
Rear heated oxygen sensor (HO2S) control is disabled.

Possible source

• Misfiring
  Air leakage in the intake system
  Air leakage in the exhaust system
  Faulty fuel pressure
  Uneven compression
  Defective three-way catalytic converter (TWC).

Fault symptoms
Malfunction indicator lamp (MIL) lit.

[erikv11]

Hey the code didn't come back; it may not! I'd watch it for a while longer as you continue to diagnose.

Good job looking at the O2 sensors. How old are they? Could the downstream sensor be shot? You'll want to check carefully for exhaust leaks too. Given the age of the car these are both suspect failure points. Cats should go for much longer but it's not unusual for O2 sensors to fail around 150k.

I'd keep looking for intake leaks even though you may have effectively eliminated that as an issue. Smoke test it?

What are you checking the codes with? Can you get access to VIDA?

I'd also inspect the spark plugs, do they look like it has been running rich or running lean? How is the fuel economy?

[ionianp2]

Thank you both for your input. I put even more miles the past couple of days and no code yet. I didn't find the ECM-4801 DTC either. Would that be a permanent code? I did the mistake of clearing the codes when the light popped up.

My next step was to get a smoke machine and test it. Been wanting one for a while.

The O2 sensors are most likely original. I do have VIDA. I was using a generic ELM Bluetooth scanner because it was more portable. About three months ago I had the flex pipe replaced along with a new OEM middle exhaust installed. I'll check for leaks when I do my next oil change pretty soon.

It should be noted that I've been putting 87 octane gas lately because in my area gas was going through the roof. I know Volvo recommends premium, but would less detonating-prone gas result in a cleaner burn?

Also does anyone know of a bona-fide way to test whether the O2 sensors are working properly. I just went by the fact that I had readings.

I can check the plugs, economy has been normal.

-ionian

[RickHaleParker]

I didn't find the ECM-4801 DTC either. Would that be a permanent code?

ECM-4801 is Volvo's code for SAE generic code P0420.