Error code P0171 and P0172

shayinok · Post by **shayinok** » 10 Jul 2021, 10:42

So my 1998 S70 T5 lost boost on the highway and threw both the P0171 and P0172 codes. I replaced the MAF a few weeks ago due to some stuttering symptoms at idle. Ideas on where to start my search on the cause?

Thanks!

Post by **misha** » 10 Jul 2021, 14:11

Those codes are usually pointing to a vacuum leak.
One is lean and the other rich condition.

EricVolvo850 · Post by **EricVolvo850** » 18 Jul 2021, 21:27

P0172 system rich mixture

Post by **matthew1** » 18 Jul 2021, 21:48

Here are diagrams of the vacuum system https://www.matthewsvolvosite.com/vacuu ... 00-turbos/

Post by **RickHaleParker** » 19 Jul 2021, 03:57

Long term fuel trim, lower limit ( Too Lean, P0171 ) and long term fuel trim, upper limit ( Too rich, P0172 ).

One thing common to both DTCs is Mass Air Flow (MAF) sensor. Clean the Mass Air Flow sensor, check wiring and voltages. If none of them are the problem, replace the MAF sensor.

Cleaning the MAF sensor should be on your preventive maintenance list. Not a repair. A can of MAF cleaner will pay for itself in terms of improved fuel economy.

Post by **matthew1** » 19 Jul 2021, 10:41

Here's my P0172 experience on my 850 T-5.

Click that for a closeup photo of the vacuum line that blew off.