Diagnosing P0172 on a V70 NA (SOLVED) Topic is solved

[3p141592654]

Got a P0172 System Too Rich (Bank 1) error code on a 2000 V70 NA with 5 speed auto, the bastard of the bastard V70s.

The car runs absolutely perfectly, so this error was a bit of a surprise. A quick scan of the internet suggests a vacuum leak as a likely culprit. Logically this cannot be true, a vacuum leak would introduce unmetered air that would require more fuel not less and therefore would set a P0171 System too lean error code. Anyway, what follows is my diagnosis and eventual solution to the problem in the hope it might be of value to others.

1) Despite my doubts I went ahead and checked for vacuum leaks. A smoke machine is the way to go here but I don't have one so I did my best to visually inspect all vacuum lines and fitting. Found the 23 year old MAP line cracked,and the 23 year old EVAP purge line was disintegrating but appeared to be intact. Replaced both. The bastards have a vacuum operated air cleaner thermostatic valve that was also completely broken and I temporarily disconnected it and plugged the vacuum feed. Thinking this must have been it, I reset the codes and went for a drive. Immediately P0172 pending came back. Failure.

2) Confirm the PCV is not leaking. It is very hard to inspect the PCV system as it is tucked up under the intake manifold. I did my best to inspect the what vacuum fitting I could see at each end of the manifold, and used a bore scope to inspect the piping under the manifold although it is very hard to get good images. This is where a smoke machine would be invaluable. I did the glove test though, and passed that with flying colors so for now I concluded my 23 year old PCV system passed and I was not motivated to replace it just for the sake of it.

3) Check for leaking injectors and high fuel pressure. Put a pressure gauge on the fuel rail and observed normal pressure during idle confirming fuel pump and regulator are ok. After shut off, system maintained pressure indefinitely so the injectors appear to be good and were not leaking (not bad after 23 years and 300000 miles).

4) A while back I had got a P0118 engine coolant sensor code that went away when I cycled the connector to it. Although the temp gauge read normal I replaced the sensor anyway on the off chance it was the problem. No change. P0172 did not go away.

5) MAF sensor. I am not a big fan of cleaning MAF sensors so this car in its 23 years of existence had never been cleaned. Some research suggested that a dirty hot wire MAF will read high and cause a rich indication. Its a simple task so I pulled off the air cleaner lid and cleaned it with MAF cleaner. Bingo, a quick drive showed no codes pending. Problem solved.

[scot850]

Well done indeed! I think the use of MAF cleaner is often under-rated. I pulled 3 MAF's from 3 junkyard cars and was amazed at 2 were really dirty and one was much less so.

I fitted one to a friends car where the MAF had failed and the car was needed on a daily basis. New MAF's are NLA from Bosch, so had to buy one from Volvo which took a week. Hence the stash from the junkyard. Fitted one of the MAF's and car was back up and running great and continued to do for 4 weeks when the owner had time to drop the car and new MAF off for fitting.

One of the issues with MAF cleaning is people not using MAF cleaner but carb cleaner or electrical cleaner and flooding the part too. Short burst of MAF cleaner should be sufficient and then let is dry off before re-fitting.

Neil.

[3p141592654]

Thank you. Yes I did some research on MAF cleaner (isohexane) and concluded its not just over priced carb cleaner but something special that is worth the extra money. Because this car is a bastard V70 it has a Denso MAF. Probably why it lasted 23 years without any cleaning.

P0172/P0171 and the Evap Small Leak P0455 are the codes I dread. So many possibilities and so little to go on. Hence why I posted this. Hope it saves others time and uncertainty.

[scot850]

We will all appreciate you sharing this with us!

Neil.

[erikv11]

Got a P0172 System Too Rich (Bank 1) error code on a 2000 V70 NA with 5 speed auto
...
A quick scan of the internet suggests a vacuum leak as a likely culprit. Logically this cannot be true, a vacuum leak would introduce unmetered air that would require more fuel not less and therefore would set a P0171 System too lean error code.
...

With a vacuum leak: the ECU detects lean, overcompensates fuel supply across the board to protect the engine, engine runs rich, P0172 sets.

...
5) MAF sensor. I am not a big fan of cleaning MAF sensors so this car in its 23 years of existence had never been cleaned. Some research suggested that a dirty hot wire MAF will read high and cause a rich indication. Its a simple task so I pulled off the air cleaner lid and cleaned it with MAF cleaner. Bingo, a quick drive showed no codes pending. Problem solved.

I have posted at least a dozen times on this forum that MAF cleaner is generally worthless. I humbly eat crow on this one, nice fix!

[abscate]

CC5343C7-C45D-4B3F-9894-7E09B4E81B82.jpeg (17.54 KiB) Viewed 4474 times

Not this guy…we keep it classy here…

B7C6CFA5-89D4-401A-8AED-1C337E83B759.jpeg (18.33 KiB) Viewed 4474 times

[erikv11]

Careful with that!!

Unless properly prepared before serving you are at risk to contract a case of ...


.

Corvids-19

.


Corvid-19.

[abscate]

The material on Mvs just keeps getting better….

[rolsen11]

Ah, the beauty of forums. This is exactly the information I was looking for. My car is experiencing a persistent P0172 that started showing up a few months ago and has gradually gotten worse to the point of throwing a CEL just a short drive after erasing codes. I have a smoke tester on order to help with this and the P0455 small EVAP leak code. I already have some MAF cleaner so I'll give that a shot. I doubt its the O2 sensor since I replaced that a few years ago.

Funny, the two dreaded codes mentioned in this thread are the two codes I currently have

[rolsen11]

Here are photos of the code and the freeze frame data for those of you who understand fuel trim values better than I do.