About 2 months ago, the check engine light came on for our out 2015.5 Volvo T5 XC60. It was a P0420 "Catalytic converter system, bank 1 - efficiency below threshold". Before I could even call the dealer, it went off (I think after 3 run cycles). Came back again a few weeks later, and once again went away after about 3 run cycles. Now it just did it for a 3rd time. I want to bring it in, but was a bit put off when the dealer told me it would by $290 just to put the car on Volvo scanner and see what is says. Being a bit tired of working with this dealer over the years, I called a highly reputable Volvo auto shop and got pretty much the same response. Why so much? I know this is more than just a simple ODB II scanner pulling out a code. Supposedly it checks all computer modules for all codes and "status", and reports anything out of the ordinary. But it's still just a computer doing all the initial work, and seems it would take little more than a few minutes. Sure, the mechanic would need to then spend time looking into anything out of the ordinary that the computer reports, but it seems this would be added labor after the initial scan, and the initial scan should be fairly quick and cheap. $290 is a lot to pay just to find out, for example, that one of the O2 sensors is on the fritz (and still need to pay to replace it).

 

If you had an O2 sensor that was not reporting correctly - you would probably get a code related to that 1 O2 sensor. You have 4 on your engine.

Your cat efficiency code - (420) The front O2 sensor/s measures the free O2 left after combustion, then the rear O2 sensor/s measures how much O2 is left after the catalytic converter does what it's supposed to do. The Front converters job is to convert HC and CO (using the available O2) into CO2 and H2O. If there is too much O2 left at the rear sensor - (meaning the cat is not converting what the ECU thinks it should be) It will set a cat efficiency code.

The solution - unfortunately sometimes that requires new catalytic converters - and on your car those are part of the exhaust manifolds. The manifolds might cost close to $2000 EACH. Plus installation.




I'm sorry, having worked on these cars for 40 years - this new stuff (the past 20 years or so) can get very expensive to fix!

A possible cheap solution - An O2 extender - people use them to space the rear O2 sensor further away from the exhaust stream - to fool the rear O2 sensor as to what is really happening. (if you want a cheap way to keep the check engine light off)

Or possibly someone will suggest 4 new O2 sensors, then when the code comes back, suggest two new manifolds. And that will certainly cost more than the $290 you are concerned about.

I understand your frustration and am glad I don't have to explain/sell this to customers anymore! Sorry for your troubles.



Edit - Sorry for some reason I based parts of my response on you having the 6cyl. For the 4 and 5 cyl engines there are only 2 or 3 o2 sensors, the converters are not part of the exhaust manifold, and there is only 1 converter. Converter still lists for about $2000.

 

Thanks for the O2 sensor related info, and insight on what the likely outcome of this will be. However, my question was geared towards why the diagnostic scan cost so much. It seems to be a flat fee to do the scan, so the cost has little to nothing to do with what the actual underlying problem is. If I had to guess, I'd say that Volvo charges some exorbitant licensee fee each time the repair shop does a scan, and the repair shop has no choice but to pass this on to the customer.

 

Hello! I have a 2010 XC70 T6 and having the same issue. I took my car in for the $290 becuase I was traveling out of state. The dealership said it was a valve on top of the engine and that might do it. All the information that they got from the cars computer said it was the catalytic converter OR both of the O2 sensors. I chose to spend $900 to replace the valve on top of the car. (there is a long story of that dealership putting a defective part on my car). What I noticed driving from Chicago to California is that the higher the ethanol the light came on. Certain gas stations especially in Iowa made that happen becuase they put a lot of ethical in the gas. Since being back in California, I can only use Berry brothers and Chevron gas. If I use any other gas, no matter what the grade, the check engine light comes on. I had to get a smog check recently to get my license tag. I filled my tank with the gas I knew would made the check engine light go off and got the smog check and it cleared! I was so relieved. I'm determined to to talk with a mechanic or someone that can diagnose this correctly instead of them saying, "well you could try replacing the 02 sensors and if that doesn't work replace the catalytic converter. That total would be around $3500. I want a definitive answer!