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Discussion Starter · #1 ·
I drive an '03 S60 S non-turbo. 5-Speed Manual Transmission, 2.4 L 5 Cyl.

The reason I've joined here is to benefit my car mechanically and make the most educated decisions!

The prompting of this is the notion that I've probably blown my catalytic converter and I'm trying to find out how to identify the issue and be positive that it is the CAT. My "Check Engine" light is on and the code is "P0-420". I've attempted to remove an 02 sensor to promote free flow but can't get either one out. I have the 02 sensor socket but both are in awkward positions on the car so I can't get a good grab at them.

If it is in fact the CAT, is it okay to straight pipe it between the bolt flanges for a time until I can afford a new one and do it the right way??? If I disconnect my 02 sensors, is it okay to leave the connections taped & tied up beneath the car?

HELP! :)

Any responses are appreciated!

The last thing I want is to cause damage to the engine! I have just above 110,000 miles on it, original clutch and perfect maintenance records! As of now the engine surges under acceleration. When the engine is cold and I reach the stop just outside my driveway the car has stalled upon pressing the clutch and stopping. It takes about a minute to reach 65 mph when the engine is fully heated and surges all the way up regardless of the pressure I have on the accelerator.


· Registered
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The catalytic converter has an oxygen sensor in front and behind it. When the vehical is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar.
This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

A code P0420 may mean that one or more of the following has happened:
Leaded fuel was used where unleaded was called for

A damaged or failed oxygen sensor (HO2S)

Downstream oxygen sensor (HO2S) wiring damaged or connected improperly

The engine coolant temperature sensor is not working properly

Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe

Retarded spark timing

The oxygen sensors in front and behind the converter are reporting too similar of

Leaking fuel injector or high fuel pressure

Cylinder misfire

Oil contamination

Some suggested steps for troubleshooting a P0420 error code include:
  • Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
  • Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
  • Inspect the downstream heated oxygen sensor (HO2S), replace if necessary
  • Replace the catalytic converter
Overall probably the biggest mistake vehicals owners make when they have a P0420 code is to simply replace an oxygen sensor (H02S). It is important to do proper diagnosis so you're not wasting money replacing parts unnecessarily.
We strongly recommend that if you need to replace the catalytic converter that you replace it with an OEM unit. Second choice would be a high-quality replacement part. There are many stories in our forums where folks replaced the cat with a cheaper aftermarket one only to have the code return shortly thereafter.
One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited milage warranty on these items. It's worth checking into.
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