Hi,

I recently changed my front o2 sensor, in order to fix an engine light being shown. I believe that the reason being it was a universal sensor, and you need a genuine volvo one for the engine light to knock off.

I have now tried two genuine lambda sond sensors, and still having issues.

With the most recent sensor, the light seems to stay off if you erase the code - but the car is "chugging". Have been told by mechanic that this is known as hunting, in which the rear sensor is looking for a signal from the front, as it isn't sending any. This results in you not being able to push down the accelerator when driving, and having to constantly jump through the gears in high revs until it fixes itself. After a good run, it doesn't seem to occur - only when you start the ignition. The mechanic tells me that the car just needs a good bit of driving for it to sort out - it definitely is running better after a drive now, but still a bit of this chugging happening. Does anyone have experience with this issue and can offer some insight

Thanks

Car is 1st gen s40 2004, 1.6 petrol engine.

 

What is your CEL? Probably a fuel trim issue I bet. Fuel trim is adjusted by the front O2 sensor. You replaced a few sensors for no reason most likely. Check fuel pressure, and intake leaks to start after getting the engine light checked.

Rear O2 sensor is just for monitoring the catalytic efficiency and does not affect how your car runs.

 

Check engine light was for a o2 sensor bank. Didn't say anything to do with fuel pressure...

 

And that CEL means you likely have a fuel trim issue, especially if you replaced the sensor 3 times and see no change.

 

What would you recommend the best way to diagnose/fix a fuel trim issue?

 

I would start by checking the car with a scanner that can communicate with all the modules and see what error codes are present. Then check for any intake leaks like broken/cracked hoses etc. You can do this visually, with a smoke machine, or using a combustible aerosol like carb cleaner.