Hi, I have a 2012 XC70 3.2 Plus running on gas (no diesel). It has 52.000 miles (84.000 km)

I had to change one of the oxygen sensors last year (the one in front of copilot) and the check engine light is on again. The problem is the two front oxygen sensors, including the one I've replaced last year. Volvo official service went thorugh the codes, cleaned the oxygen sensors and finally said I have to replace both catalytic converters that it's going to be a fortune (XC70 3.2 Plus has two CATs). I can't believe I have to change both CATs, any idesa/opinions/advise?

Thanks..

 

I'd start by doing a full check for intake air leaks (ie via smoke test) and listen/feel for exhaust leaks. Also do your own scan to see what codes are being presented (you can borrow a code reader at a big box parts store or by a $39 scanner from Harbor Freight). Typically a bad catalytic converter is associated with a P0420 or a P0430 code which are defined as the catalytic converter is operating below efficiency. What is really going on is your emissions systems are defined around bank 1 (ie right side of a V6 or V8 or the I4/I5s) and bank 2, which is the other side of pistons on the V engines. Each converter has two O2 sensors - the front is the "lambda sensor" providing feedback to the ECU on whether there's too much or too little oxygen in the exhaust (too little O2 means car is running rich, too little O2 means its running lean so the FI will compensate. The rear O2 sensor is there to measure O2 remaining after the HCs are burnt in the converter. The ECU calculates a delta between the front and rear sensors to determine if the converter is doing its job effectively. If the sensors are at fault, a check engine code can identify which sensor (front, rear by bank) and why. If a fully equipped shop sees a 0420 or 0430 fault, they know which converter is acting up and can use a heat sensor to see if the converter is heating up to proper temperature to do its job. So why are you getting a CEL? you could have an air leak or exhaust leak that is throwing off the O2 sensors, you could have used an after market sensor which is not at the same tolerances as the OEM parts or an incorrect part or one or both converters could go bad. If it turns out the converters are both bad, then you'd really need to ask what can cause the converter to fail at 50K miles. Are you consuming oil or coolant which can leave deposits on the grid inside the converter? Is your car easily meeting emissions or showing other signs of running rich or lean? Are you getting false positives? I've set off this code by starting and stopping the engine in very short succession - so what happens when you clear the code - does it return in 50 miles? in a week, a month or right away? I'd really be surprised that both converters can fail on their own so replacing both doesn't seem like its getting at the root cause. If just one failed, then I'd be thinking bad part, bad cylinder etc. Both makes me wonder if something else is going on and the cats are just taking the blame.

 

Many thanks. The official Volvo service has checked for leaks and everything else, they cleaned the sensors this week and reset the error. I think the same, very strange I have to change both converters (and it's a fortune). I'm the second owner of the car for a while and I've only used superb gas, no oil or coolant, all maintenances in the Volvo official service. I'll drive again the car and see what happens, otherwise I'll go to another Volvo service.
Regards.