XC90 Flashing check engine light after turbo replacement

Hi all,

I'm stumped at an issue I'm experiencing on my 2006 XC90. The turbo in my 2.5T petrol was leaking loads of oil, so I had my local mechanic replace it with a refurbished unit from Reflex Automotive. Straight after I got it back, I started getting a flashing check engine light, but only if I am coasting down a hill. Doesn't do it under load, just sometimes when I crested a hill and was coasting down the other side. Also seemed to only happen when warm, never straight after engine start. The flashing light would last about 7-10 blinks. Sometimes the check engine light would set after flashing, sometimes not. The codes would be random misfires or a misfire for a particular cylinder, but not always the same cylinder. This makes me think it's a sensor like the knock sensor, but the mechanic was saying he didn't disturb that at all.

So the mechanic checked it all over, re-seated all the connectors and cleaned them for anything that was disturbed to get the turbo out. He replaced the plugs and coils. He checked all the physical connections were tight. But still the problem remains. I always run the car on premium 98 fuel.

The car runs beautifully, not rough at all, in fact if it wasn't for the light, I wouldn't even know there was a problem. I'd be tempted to leave it but of course there's no way of knowing if there is a serious check engine problem that arises, because the check engine light would already be on.

I'm a little lost to know where to go from here. If anyone has any suggestions, I'd be mighty grateful. If I make any progress in the meantime, I'll post it back here. Cheers.


  • I'm actually wondering if it could be a bad batch of fuel. I filled it up just prior to taking the car in. It still has a fair bit of the tank left, but if it runs low and I haven't managed to solve the issue, I'll be interested to see if it changes anything. Seems unlikely though.

  • interesting a flashing engine light , is there a message as well in dash as interested into the flashing light so maybe snap a pic

  • Nah no message in the dash at all. It's hard to get a picture (well, video) of it flashing because it only ever happens after cresting a hill and coasting down the other side, and only sometimes. It never happens while stationary to make it easy to record, so I'll need to setup a camera in the car.

  • 2 thoughts

    #1 he would have touched the o2 sensor with the work he did and could have done something funky to it

    #2 what plugs? Volvo branded or other?

  • 1: Yeah I believe the rear o2 sensor was moved to get the turbo out. He did double-check that all the connections were good when he put it all back together. It's been on my mind as a possible cause. If I can't come up with any better idea, I might just replace it and see if that helps anything. Good tip.

    2: We pulled Volvo plugs out of it and put in aftermarket plugs, didn't change the problem. Random misfire occurred on both.

  • Ex850RSnoopy (@Ex850R) Somewhere Over the Rainbow. Melbourne.

    *use only Volvo brand plugs.

  • edited February 24

    Do the aftermarket ones cause issues or just have a shorter life? For me the performance has been the same with either.

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