2004 S60 PO172 not turning off after repairs

stevolvos60 · Post by **stevolvos60** » 03 Oct 2014, 12:58

Volvo is s60 2004 2.4, 5 valve non turbo with 125000 plus miles. My friend is mechanic doing the work. Had PO172 and code for rear O2 sensor. Car was misfiring at idol almost stalling out. Car was sluggish when gas pedal was applied. So far replaced rear O2 sensor ,also replaced oil trap and hoses{kit} and MAF sensor, cleaned injectors and throttle body. Misfires still at idol and sputters with take off from stop. It runs better but after repairs the engine light /code PO172 stays on; still have some hesitation with idol and misfires especially if a/c is on. What am I missing in the system checks. No other codes are coming up. No indication front O2 is bad. No other system checks show failures.

In addition, the fuel rail pressure is currently 55 psi. I hope I gave enough information.

Does forum have system specs for this vehicle? I want to avoid duplicate questions. New to site

Thank you.

Post by **abscate** » 04 Oct 2014, 03:59

How many miles are on the spark plugs? At 125k miles, the front O2 sensor is certainly due for replacement, so I would do that if you want to keep the car longer term

draser · Post by **draser** » 04 Oct 2014, 09:23

Honestly I had no idea what p0172 was so I looked it up. Fuel system too rich.. Too much fuel not enough air... so for some reason the MAF sends the wrong signal to ECU which opens up injectors too much. Like suggested front oxygen sensor can do that, they normally fail on the rich side. Good advice to replace like said. I'd also pull the plugs to see if they're all wet with gas or maybe just one is more... which would point to leaky injector.

stevolvos60 · Post by **stevolvos60** » 13 Oct 2014, 09:13

Thank you. front 02 did the trick, 4 wire denso sensor used. Drives better than ever now.

DrJammer · Post by **DrJammer** » 15 Oct 2014, 14:44

I have the same code on an 04 V70 non turbo with 75,000 miles. Is there an easy way to determine if the MAF or front O2 sensor is the issue? I have tried a used OEM MAF, but it looks crappier than the original. I am thinking I need to try a brand new MAF since there is NO change when I unplug the MAF.

I don't want to buy a more expensive MAF if the O2 sensor is the issue.

Thank you

draser · Post by **draser** » 16 Oct 2014, 05:15

Very good question. To decide whether is MAF or O2 sensor you need to know their signal level and behaviour for a good running engine. To get that info you'll need a blue tooth OBD 2 adapter ($ 20) on Amazon and Torque app for your phone. The free version of the app gives you both readings.

hermechanic · Post by **hermechanic** » 21 Oct 2014, 09:17

A quick and dirty test of the MAF sensor is to unplug it and see if it runs better. ~Steve