P0171 & P0236 codes

jchrisf · Post by **jchrisf** » 22 Apr 2011, 15:47

Recently my 2001 Volvo S40 T1.90 has been throwing codes PO171 and PO236. Today I cleaned the MAF with CRC MAF cleaner. When I first took the car out for a test drive it was running like I have never seen it run before (great). Then I tried WOT at 50mph to test a passing situation. The car kept hesitating and then accelerating the whole time(hesitate, accelerate, hesitate, accelerate, etc.). I tried this about a six times and it did the same thing every time. Twice I could hear a clicking sound... don't know what that was. Then when I came to a stop light it idled fine but when the light turned green is hesitated a lot. I thought it was going to stall but it didn't. It ran fine while I was driving normal but would hesitate when I started from a stop or accelerated fast. Then it started running fine again while I was driving normally. Anyone got any suggestions on what to do next or what this might be? Occasionally when I stop at a light and it idles for a while... as soon as the light turns green and I release my foot from the brake the engine will die. It will rev-up in neutral fine but not accelerate fast without a lot of hesitation.

Post by **VCA** » 22 Apr 2011, 16:03

jchrisf wrote:Recently my 2001 Volvo S40 T1.90 has been throwing codes PO171 and PO236. Today I cleaned the MAF with CRC MAF cleaner. When I first took the car out for a test drive it was running like I have never seen it run before (great). Then I tried WOT at 50mph to test a passing situation. The car kept hesitating and then accelerating the whole time(hesitate, accelerate, hesitate, accelerate, etc.). I tried this about a six times and it did the same thing every time. Twice I could hear a clicking sound... don't know what that was. Then when I came to a stop light it idled fine but when the light turned green is hesitated a lot. I thought it was going to stall but it didn't. It ran fine while I was driving normal but would hesitate when I started from a stop or accelerated fast. Then it started running fine again while I was driving normally. Anyone got any suggestions on what to do next or what this might be? Occasionally when I stop at a light and it idles for a while... as soon as the light turns green and I release my foot from the brake the engine will die. It will rev-up in neutral fine but not accelerate fast without a lot of hesitation.

I suspect your turbo wastegate isn't opening (due to either, in order of likelihood, a broken/missing vacuum line, a stuck turbo control valve [TCV], or a physically stuck wastegate), that or there's a leak in the piping leading from the turbo to the intake manifold. Hopefully someone with more experience on these cars can chime in with specific location of parts, but usually, the TCV is nearby to the airbox and has three hoses and one electrical connector going to it.

jchrisf · Post by **jchrisf** » 27 Apr 2011, 04:33

Thanks VCA.. can you or someone with an online manual post pictures of the location of the wastegate... I know where the TCV is as you have described it... can't remove the air filter without dealing with it. What do I do to check the TCV?

jchrisf · Post by **jchrisf** » 24 May 2011, 19:50

I think I have finally resolved this problem and wanted to post what I found in case someone finds this with the same or similar problem in the future. I want to thank everyone for their help. When it came down to it it was this post that was identical to my problem and sent me on my way to a resolution:

www.matthewsvolvosite.com/forums/viewtopic.php?f=8&t=24818&p=106003&hilit=fuel+filter

I think the cause of most of the confusion is that I seemed to have two different issue arise at once. The only one that coded was the MAP issues. I replaced the MAP sensor and my codes went away but the symptoms the car had did not. Incidentally there was a poster who had a similar issue and the exact same codes and he replaced the MAP sensor on the air intake by the intercooler (which Haynes actually calls the Intake Air Temperature Sensor but it is identical to the MAP sensor) however it was the MAP sensor on my intake manifold where the fuel rail is located that I had to replace.

The car ran and started perfectly with an occasional hesitation at idle but didn't happen much and was gone as soon as it started. I could not accelerate hard past 1/4 throttle or the car would start hesitating like crazy and if I keep my foot in it the check engine light would start to flash for a few seconds and then go away.

Once I read the post from the link above I decided to start concentrating on the spark plugs. I replaced them and it ran much better but still had a slight hesitation at WOT. Then I replaced the coils and spark plug wires and the problem is gone. Those codes had my attention focused on the boost and it's related sensors but when I was not getting anywhere I started thinking it was the fuel filter. I did a search on that and came to the post above which was identical and there I found my solution.

Post by **billofdurham** » 27 May 2011, 12:04

Thank you for the update. The search feature is a great thing.

Bill.