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Volvo PO172 Explaination and Fix

Volvo PO172

The Volvo PO172 code should not be ignored

If you’re getting the Volvo PO172 code, Basically this means that an oxygen sensor in bank 1 detected a rich condition (too little oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1. You will more than likely not notice any drivability problems, although there may be symptoms such as a misfire.

A Volvo PO172 code may mean that one or more of the following has happened:

  • The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of “oiled” air filters can cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
  • There could be a vacuum leak.
  • There could be a fuel pressure or delivery problem.

Possible solutions include:

  • Inspect all vacuum and PCV hoses, replace if necessary
  • Cleanthe MAF sensor. Consult your service manual for it’s location if you need help. I find it’s best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it’s dry before reinstalling
  • Inspect fuel lines for cracks, leaks, or pinches
  • Check the fuel pressure at the fuel rail
  • Check the fuel injectors, they may be dirty. Use fuel injector cleaner or get them professionally cleaned/replaced.
  • Check for an exhaust leak before the first oxygen sensor (this is unlikely to cause the problem, but it is possible)

MVS Forum Member Guest asks:

So this is the code (Volvo PO172) that I pulled my from 97 850 NA, this site has the possible solutions to the problem

I know its not the MAF sensor because I replaced that, I checked the white vacuum lines and they looked fine. How can I check the fuel pressure at the fuel rail? What else shall I look out for? Thanks in advance.

MVS Forum Member Tsquared adds:

I have had the Volvo PO172 code for about 2 months. I had recently replaced the O2 sensors so I was fairly sure that was not the problem. Tried a new MAF – no joy. Started looking at my vacuum elbows and found a few that were starting to deteriorate. Replaced all of them around the throttle body and intake area and followed them to the distant end and replace it as well. I still had the problem. I purchased an extra set of O2 sensors and tried that – still no joy.

I finally found a broken vacuum elbow on the front side of the engine that was the problem. It was located facing the front of the car about half way down the block near the timing cover.

I was able to use the rear O2 on another vehicle. I have a spare front O2 that has about 12 hunderd miles on it. Mew MAF on the car and good MAF with 125K miles sitting on the shelf. I now have 2 weeks to get the emissions test completed – cutting it too close for comfort.


MVS Forum Member voltech1 replied:

You have a system too rich code lower limit. A vacuum leak will cause a(upper limit) lean condition and usually when a MAF dies it goes upper limit but not always. Check your ETC coolant temp sensor under the waterneck on top toward the front of the motor. If it looks scaley or coolant is coming out of the two wires replace it. The ECU will dump fuel if it thinks the car is even a little warm. If ECT is cruddy looking replace the thermostat at the same time.

PO172 Explaination and Fix


what’s next in probable cause p0172; done your recommended
pvc overhaul confident i have no vacuum leaks did a “propane” test on o2 sensors ehhh ok ideas?

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