P0172 Engine Too Rich

I think I posted here or maybe on one of the brickboards about a similar problem on a '99 V70 T5.

I was never told what the code was but the problem was fairly obvious and was caused by the airbox to turbo hose left completely undone by the mechanic on a top engine mount change. I am surprised that the CEL goes way and comes back unless you disconnect the battery to temporarily clear it.

Running too rich is caused by over-fuelling and although the cause can be various, the most common cause appears to be an air leak around the inlet path which fools the sensors into adding too much fuel which is seen by the outlet sensors as way too rich. In my extreme case of probably about 50% extra over-fuelling the symptoms were that the car went like a bullet on steroids but wouldn't do more than 17MPG. The soot build up was rapid and after a couple of hundred miles the black smoke at tick over was a complete assurance of much too rich.

If yours is not a turbo there is frequent reference to a 90 degree elbow which splits and that is a common cause. You are dealing with a series of dependent factors which start with the air box and MAFF sensor on through to feed air and vacuum pipes then to plugs\leads exhaust and the O2 sensors.

My cause was obvious but the plugs were soot black (only a week old) and were thrown away, the first O2 sensor was faulty which was as a direct result off excessive soot contamination.

I have gone through this long winded explanation to try to highlight the cascading domino effect that a small problem can have throughout the system. The reason why is to caution against coming to a too rapid conclusion and the logic is from an owner who had a catastrophic sequence of repetitive failures. In that person's situation the fault was throwing a code and sensor after sensor was changed, because they were responsible for throwing the code but the eventual fault proved to be the Electronic Throttle body. Not a cheap job but when you add three sensors to the bill it was one heck of an ouch! bill.

The lesson I have learned from my two experiences and other people's more catastrophic experiences is that a garage had be 100% sure that if a fault caused the sensor to become faulty they had better be 100% sure that it is cleared before they stick a new £300+ one in. I am reliably informed that a bad over-fuelling fault can cause a brand new sensor to be only fit for the scrap bin in 20 to 100 miles.

Good luck with your investigation and hopefully it will be something very low cost. BTW although mine is a '99 the same may be true of your model... O2 sensors have been modified and the older ones cannot be found anywhere... A Vadis software upgrade is needed for the only ones available to work retrospectively. It means the prospect of a main dealer fit and fix as the only option if a new sensor is required.

Liam

This code is caused by low fuel pressure, a bad MAF sensor or vacuum leaks. Most of the time it's vacuum leaks, check the vacuum elbow on the end of the intake manifold right behind the power steering pump first.