P0172 Solutions

washdup · Post by **washdup** » 17 Apr 2012, 08:25

Makes sense.

washdup · Post by **washdup** » 20 Apr 2012, 18:53

Turns out it is in fact the vacuum elbow under the thermostat, as erikv11 suggested. That elbow is missing on my car. All I can see is the end of what appears to be the vacuum hose that runs over from the fresh air tube. It looks like that hose has insulation around it (making it appear to be a larger hose than it is). Is this elbow = "coupling piece" p/n 9155862? I can't see how it connects or where.

Post by **matthew1** » 20 Apr 2012, 20:56

The factory Volvo routing is elegant, but not robust. Here is my robust, but not elegant solution: https://www.matthewsvolvosite.com/forums ... 00#p233700

Does away with several elbows, including the Evil P0172 elbow. Has worked well for 6 weeks.

Form follows function.

washdup · Post by **washdup** » 21 Apr 2012, 16:24

Turned out the other elbow at the fresh air tube was also toast. I used some spare silicon hose and made an inelegant, but hopefully robust, path under the vacuum tree (carefully avoiding the throttle linkage) and under the fuel rail. Idle is back to normal and the car is running sweet(ly) once again. Thanks, MVS!

babadoeke · Post by **babadoeke** » 30 Aug 2012, 12:06

My 98 s70 has had this code for about a month now. I've read through this thread and have some symptoms no one else mentioned. Perhaps someone could help me narrow down the possible code triggers based on these symptoms.
Every morning when I try to start the car, it struggles to start and usually won't start the first time. However, the second time I turn the ignition, it starts just perfectly. And subsequent starts throughout the day are fine.

Is this behavior typical of a vacuum leak?
Or could this be a faulty canister purge solenoid?

For some reason, I don't think it's the O2 sensor due to the very consistent start pattern every morning. But I'm not a mechanic and know very little about these things. Be gentle.

Post by **matthew1** » 08 Sep 2012, 12:45

See if you have pressure at the fuel rail after turning key to position II. That's the position right before the starter engages. You'll hear the pump running.

wjkjr · Post by **wjkjr** » 10 Sep 2012, 22:54

babadoeke wrote:My 98 s70 has had this code for about a month now. I've read through this thread and have some symptoms no one else mentioned. Perhaps someone could help me narrow down the possible code triggers based on these symptoms.
Every morning when I try to start the car, it struggles to start and usually won't start the first time. However, the second time I turn the ignition, it starts just perfectly. And subsequent starts throughout the day are fine.

Is this behavior typical of a vacuum leak?
Or could this be a faulty canister purge solenoid?

For some reason, I don't think it's the O2 sensor due to the very consistent start pattern every morning. But I'm not a mechanic and know very little about these things. Be gentle.

[I am experiencing the exact same thing with my 96 850. I pulled the codes and I am getting P0172 and P0455. Hard start in the morning and the rest of the day is fine. I cleared the codes and will check again to see if I get the same thing. This has to have been addressed before. I have to defer to the experts for this one.]

yurimpala · Post by **yurimpala** » 17 Jun 2015, 11:58

I am having this P0172 code in my 95' Volvo 850 N/A. The short term fuel trim and long term fuel trim are varying from +14 to +25. The engine is new (1500 miles after rebuild), all vacuum hoses are new. I double, triple checked the vacuum for possible leaks. The two O2 sensors are new (bosh). The pressure regulator is new. In the Service Manual I found that the fuel pressure in the rail has to be 43 or 44 PSI, and my car is showing around 20 - 22 PSI. I changed the fuel filter (the older was clogged, and probable is the cause of this trouble). I measured the pressure on the check valve prior to the fuel filter and the pressure remains in 22 PSI. Because of running the car so long with the fuel filter clogged, I guess the fuel pump was overloaded and lose their properties. Now I purchased a new fuel pump and I'm waiting the delivery. When I install the new pump and have the pressure in the rail restablished, I will let you know.

yurimpala · Post by **yurimpala** » 19 Jul 2015, 14:29

After installing a new fuel pump, nothing changed. The P0172 came a lot of times. Looking for a possible solution, I found some information on EGR System. I had cleaned entire system when I rebuild the engine. But I suspected the EGR Controller since there is no voltage on their terminals. Yesterday I made a lot of tests on EGR System, but found nothing.
Today I found on Youtube a video that help to test vacuum leaks with smoke. It's a very clever way to test it. Here is the link of the video:
So, I made a smoke machine and injected the smoke into the Brake Booster Hose and I found one leak on the Brake Booster Hose Junction and one leak on the EVAP system near the Throttle Body.
I fix the leak on Booster Hose with a pair of clamps. And I fix the EVAP leak installing a O-ring on it.
Now the Long Term Fuel trim is 7.4% and Short Term Fuel Trim is varying from -4.3 to 4.5%.
In the course of the week I will monitor those parameters to certify that the problem is corrected.

P0172 Solutions

Re: P0172 Solutions