My 2001 S60 non-turbo has around 190K miles and still runs great -- gets 28-30 mpg and even more on trips w/cruise control. Several months ago, the check engine light came on. Took car to independent shop that does all my cars. Code indicated a bad thermostat, so this was replaced. Check Engine light returned a week or so later. Hmmm? Took car back to same shop -- different code -- bad (inefficient) catalytic converter this time -- shop replaced with a non-Volvo replacement approved for use in California that looked identical to original. Check engine light returned in a week or so. I bought Innova code reader to check for myself -- same code reading P0420 (Catalyst System Below Threshold - Bank 1). This is getting expensive and frustrating. I know the problem could be the non-Volvo converter, but I hate the thought of replacing the converter with a Volvo part. Could the computer need to be checked and/or adjusted? Any help and/or advice greatly appreciated.

Frank

 

The code is for the oxygen sensors. That is probably what killed the converter. You can have each one tested at a shop. It could be one or both that are bad. Prices vary greatly on replacement sensors.

 

The rear 02 sensor will indicate whether the cat is doing it's job. If not, it will set off that code, so I suspect the 02 sensor is working. I have installed aftermarket cats on a couple vehicles and encountered the same problem. The "fix" is to weld an additional threaded 02 sensor bung on top of the one on the cat now and thread the 02 sensor into the newly extended port. This moves the sensor out of the direct path of the exhaust gasses.

I had a car with a bad cat (Geo Metro) and I got a junkyard cat to replace it. The replacement cat was not melted down, but was not functioning properly, so I removed the rear 02 sensor from the port and plugged the hole. The sensor is tied up on the frame rail plugged in and the check engine light stays out.

I feel that some aftermarket cats do not have enough of the precious metals and other materials required to meet the standards of certain vehicle monitoring systems.

 

Many thanks for the advice. I did try replacing the rear 02 sensor with a generic 4-wire Bosch. Original sensors are Denso. The new Bosch didn't change anything. Next, I took the rear sensor out, taped it out of the way, and plugged the rear hole with the old Denso. Still got the Check Engine light -- this is what made me wonder about the computer that monitors the exhaust, etc. I replaced the Bosch with original Denso. Back to the same-old, same-old Check Engine. I suspect the aftermarket converter may not have the specs to replace the original Volvo part. I'm sure that's what Volvo would tell me.

Frank

 

I've had this problem recently. Light on/off, code 4801. I've been told the cat. needs replaced by dealer, independent Volvo repair verfied the same code, said the car is running fine, and dealer just wants to sell me a new cat @ $1200. So I posted problem and was told by Tech that its probably the injectors, which can damage the cat., seems to make sense from studying the overall system, since my cat seems fine.
This is what I've noticed when the light came on the 1st time(and other times); I did not let engine/turbo cool down after a long highway drive before shutdown. When I started it back up and got back on the highway, I noticed the check engine light was on. Hmmm...........something to keep in mind. It came on a few times after that till I started piecing it together.
So what I've done now is make sure turbo cools down before shutdown. Replaced fuel filter as the old had not been changed at the 90k service interval like I was told it was by person who sold it to me. Running a 2nd tank right now of fuel with BG44K to clean out the fuel system, valves and combustion chambers.
The light has not come at all in past 400 miles. Before it was coming on much sooner. Did I fix it? Time will tell. You have a lot more miles than I(97k), which is nice to see. Anyway I will do the injectors if the light comes on again. I was told by Tech that bad injectors can damage a catalytic converter. This is why I am cleaning the fuel system 1st. Could have have a semi-plugged injector and this may fix it. Good luck to you.