Engine: B5244: S80 OBD Code P0172

[Bernard46]

I have a 2001 S80 Petrol 170 bhp auto with about 140,000 miles on the clock. About 4 weeks ago it had the cam belt replaced for the second time (nearly 15 years old) and an MoT test. It failed the emissions test because the lambda sensor was kaput - no reading from it at all. Replacing the lambda sensor put the emissions back in the middle of the range where they have always been (by the way there were no codes or lights on the dashboard to indicate there was a ever problem with the O2 sensor).

Everything was fine for a week when suddenly on start-up the "Emission System Service Required" message and the engine light came on - the car had previously been driven about 12 miles and left for 2 hours, so the engine was partially warm. The message and light stayed on through several subsequent starts. Having connected an OBD code reader I saw P0172 and following research on this code I open the bonnet and poked around the engine looking for any obvious broken or leaky vacuum pipes, but couldn't see anything. I closed the bonnet and the next time the car was started there was no message and no warning light. This lasted for a day or so and then the same indicators came on, again on start-up. This time the lights stayed on so I booked it into my local garage (the one who had done the previous work) - not a Volvo specialist but nevertheless a competent outfit who have done good work in the past.

They are puzzled. They say the new lambda sensor is working fine and giving the correct readings, they can find no source of vacuum leaks - they tell me there is not much in the way of vacuum pipes on this engine (I personally wouldn't know where to look, so cannot verify this). They say it could be a MAF problem or it could be the injectors are leaking, but given the age of the vehicle they are reluctant to throw (expensive) parts at it speculatively.

The car drives fine, idles at the right speed, does not mis-fire at any speed and fuel economy is as good as ever. The only change at all that I can notice is that prior to the new lambda sensor there was always (for a lot of the past year) a strange burning (like metal) smell when one got out of the car after a journey and this no longer appears - probably not relevant to this problem.

If the dash light and the message were not there I wouldn't notice any issue. Can anyone throw any light on what might be the problem?

[bournricha]

The Mass Airflow meter can be removed and cleaned with made for purpose spray cleaner .Google cleaning MAF and you should come up with the tutorial on you tube I think .Don't be tempted to use anything other than the spray as the wires that measure the air flow are very fragile .They are known to get dirty from time to time and send a wrong signal to the ecu .Cleaning will only cost pennies and it is quite likely to be the cause of your code .

[Bernard46]

OK thanks, I'll get some cleaner and give that a try. I assume there will be no issue in disconnecting the sensor to clean.

I noticed I could get a replacement MAF Sensor for this vehicle on ebay http://www.ebay.co.uk/itm/ACP-Air-Ma...cAAOSwnDxUflpT for about £28 - would it be worth trying this as well? If I replaced the sensor does one need to "tell" the ECU?

[cheshired5]

Originally Posted by Bernard46

OK thanks, I'll get some cleaner and give that a try. I assume there will be no issue in disconnecting the sensor to clean.

I noticed I could get a replacement MAF Sensor for this vehicle on ebay http://www.ebay.co.uk/itm/ACP-Air-Ma...cAAOSwnDxUflpT for about £28 - would it be worth trying this as well? If I replaced the sensor does one need to "tell" the ECU?

Before buying a MAF, watch this. https://m.youtube.com/watch?v=QtQnE1QW-jU

[oragex]

Lambda sensor was an original Volvo part?

[reggit]

Originally Posted by oragex

Lambda sensor was an original Volvo part?

That's a good point, none original spec lambdas can be troublesome in these cars.