Let me start from the beginning. I scanned the car and these 8 codes popped up. The car is a 2007 lr2 with Volvo si6 3.2 engine

i sent it for an emission test and it failed. Replaced the four oxygen sensors and it’s still failed.
Carbon dioxide was on 2.5% and hydrocarbons on 167

I had asked my mechanic to please check the fuses, he said he has checked them, although I am in doubt. I don’t know where else to look

could someone please give me a shove in the right direction?

it has been suggested that there could be a leak in the admission and to do a test with smoke

Any help much appreciated

 

High emissions can result from an overly rich fuel mixture. I notice the first code in your list is about fuel rail pressure. The fuel pressure sensor is a pattern failure on this vehicle. If it's defective and sending the computer bad readings, that might result in a too-rich fuel mixture. Have you replaced this sensor, or still using the original?

When you look at live data on your OBD2 scanner, what is the fuel pressure? It should begin around 60psi for a cold start, and then settle down to 55psi.

 

the pressure starts at 765, and no haven’t replaced the fuel pressure sensor despite reading it helps since I was told it possibly wasn’t the issue. It’s clearly not doing its job though, thanks for the input, this helps a lot.

what I don’t understand though is for what other reasons the oxygen sensor codes are triggered other than faulty oxygen senses. The car at the moment has 135,000 km and I replaced the originals

 

Agree you should replace the fuel pressure sender, cheap and easy DIY.

Did you clear the codes after replacing the O2 sensors? If not those codes might just be lingering from before, so try clearing them.

Also the last code is probably for your radiator fan, either the fan or the control module. Those tend to fail, and it does tend to set a code before actually failing so that's something to watch for. If the coolant temp gauge needle moves above it's normal position, especially while idling stopped in traffic, just turn the car off. If you keep running it with the needle above normal you will break various cooling components.

 

yes cleared the codes. A few time times just for good measure and those just stayed. The radiator fan code is actually new, definitely having that taken care of asap!

just ordered the fuel sensor. The O2 sensor codes are still a mystery. The car is out getting the window winder fixed but I am suspecting the mechanic may not have checked / replaced the fuse. As soon as it’s back I’m going to double check that too.

 

This is speculating, but it's plausible that a faulty fuel pressure sensor can cause the fuel/air mixture to be too rich (too much fuel). If too much fuel is being dumped into the cats, a low voltage reading will be indicated by the O2 sensors. These codes don't mean the sensors themselves are bad, just that you have a fault condition that needs to be diagnosed for root cause.

Check the fuel trims in the live data of your OBD2 scanner.

 

My

The futures are above. They look to be negative figures. I must admit I looked at them but they don’t mean anything to me.

 

Your fuel pressure is equivalent to 110psi, if my Google calculator is working correctly for the conversion from kPa. This is so extremery high (for a gasoline/petrol engine) that the computer has probably disabled some functions like fuel/air mixture, which accounts for your near-perfect fuel trims.

This is hard for my eyes to believe. A shop should have checked these values as part of their initial diagnostic, unless I am completely missing something here. I'm sure other forum members will chime in.

 

There could be a blockage after the pressure sensor that is causing the pump to work too hard. I don't think the LR2 fuel pump can work that hard.

 

perhaps a blockage in the fuel lines? That could make sense.. what I’m concerned about is replacing the sensor for the sensor not to be the problem

how would such a blockage be detected or cleared?