DTC P2178 System Too Rich Off Idle (Bank 1)
 

The Check Engine Light on our 2011 Volvo S40 T5 came on and my scan tool shows the DTC P2178 "System Too Rich Off Idle (Bank 1)". From what I can track down, Bank 1 refers to one of the Cylinders 1,3 or 5 even though this is an inline engine. My Volvo mechanic immediately suspected a vacuum leak but could not spot a leak even using a smoke machine. He replaced the O2 sensor but the light still comes on. If the code is cleared with the scanner, it returns after about 25-35 miles of driving. Scanner data shows that the ST Fuel Trim is at -1.6% and the LT Fuel Trim is at -16.4%. Vehicle speed was 30 mph and engine RPM was 1644. MAF reading was 1.9 lbs/min. Fuel System was in Closed Loop mode. After 2 weeks, my mechanic is stumped. I've removed the MAF and cleaned it with the special MAF cleaner - it looked very clean when I removed it. The car runs without any problems and delivers 27-28 mpg on the highway with no traffic. No problems starting the car or idling or accelerating. We are contemplating the replacement of the MAF and then maybe the fuel injectors - both are relatively inexpensive parts although the mechanics labor on the injectors will be nontrivial. Has anyone ever encountered this type of problem? This car does not appear to have an EGR so we ruled that out.

did he check for exhaust leaks as well? that can throw off the O2 sensor as well. Did you run real time data to see if the fuel trim changes as the engine (and plumbing...) heats up (suggesting a leak that may open or seal with temperature)? Anything odd going on with the temp gauge? Wondering if one of the other sensors is off - ie ECT, MAP etc... Given you have a turbo, there could also be an issue in the air path from the turbo through the intercooler etc leaking some boost and messing with the ECU mapping...

Thx for the response mt6127.
Check for exhaust leaks as well? that can throw off the O2 sensor as well. - he was focused on vacuum leaks but I will ask.

Did you run real time data to see if the fuel trim changes as the engine (and plumbing...) heats up (suggesting a leak that may open or seal with temperature)? My scanner does not appear to have that capability? Any suggestions on a scanner that can display realtime data? My scanner only shows the freeze frame data and some cryptic values under the heading IPT.

Anything odd going on with the temp gauge? Wondering if one of the other sensors is off - ie ECT, MAP etc... Given you have a turbo, there could also be an issue in the air path from the turbo through the intercooler etc leaking some boost and messing with the ECU mapping... Temperature on the dashboard gauge is fine. The intake air temperature on the scanner freeze frame data seems okay. I've ordered a DELPHI MAF which is relatively inexpensive and easy to change now that I purchased the 5-star security "TORX-like" bits. I had a brilliant plan to swap my MAF with my wife's 2008 S40 (not turbo) but her MAF sensor is different. Also looking at replacing the fuel injectors as FCPEuro sells these for $18 each (as well as the $131 Volvo injector). Labor will be substantial to change the injectors (i.e. I am getting too old to spend hours getting the injectors out) so I am going to try a new MAF first. I've read that others have changed MAF, injectors and ignition coil packs/plugs and were NOT able to get rid of the P2178 code. That is discouraging. One other person mentioned the ECT sensor and it seems difficult to remove that sensor - anyone have an idea of where that sensor is located? It is inexpensive so worth changing?

I'm a big fan of the Torque Pro app (runs on my 'droid phone - not sure which other platforms it'll work with). A $10 (or $5?) app, which needs only a $10-12 Bluetooth OBD adapter to operate. With it you can build custom dashboards, selecting any number of really useful displays, including graphing for most functions if you like (I use that for O2 sensor diagnosis all the time). If you don't have a 'droid phone, there are other similar products (though most of 'em cost more, especially if you live on the Apple side of the great divide).

FWIW, I'd have to guess that your chances of fixing this with a handful of new injectors is nearly zero, and ultimately you'd probably make the car less reliable (those Volvo injectors don't fail very often, not sure that's the case with knock-offs).

Cases like this one can be really frustrating, as there are a lot of potential causes for the code. Good luck!

Update: FRustrating Journey for Check Engine Light - Rich Idle Mixture
 

Thx to everyone on the S40 Forum. I spent many hours reading through responses and this helped to guide me to a final solution for my 2011 Volvo S40 T5 for the DTC P2178 "System Too Rich Off Idle (Bank 1)" code. My independent Volvo mechanic changed the Oil Trap Assembly, which is a common problem on these cars and I tried a 3rd party MAF sensor from Delphi (which created new problems) before finally reading that many owners had problems with the fuel (rail) pressure sensor. My fuel pressure (43 psi) seemed a bit low compared to my wife's 2008 Volvo S40 2.4i (non-turbo engine at 55 psi. I ended up re-installing the factory Bosch MAF as the Delphi MAF was causing unstable engine idling and rough operation (the part fit mechanically but I wonder if it was not the proper part?).

The Bosch replacement sensor is relatively cheap from folks like FCP Euro. Removing the part was fairly easy but I ended up using a Torx bit firmly clamped in a pair of mini ViseGrips as the clearance is tight and I had Torx tools that fit in that space. Many owners reported problems with a lot of gas pouring out unless you pulled the fuel pump fuse and cranked the engine a few times. I simply went to the Schrader valve at the end of the fuel rail after packing the area with rags to catch the gas. Did the same on the other end of the rail where the sensor is installed. Luckily, not much gas came out and I had the sensor replaced in 2 minutes after that. I also purchased the OBDLINK Bluetooth version and downloaded the OBDWIZ software - very useful tool which I should have bought users ago as the standalone handheld scanners I had provided little value except to tell you something was wrong. Being able to graph and save operational data was valuable although there is little explanation of the parameters that you can log. But, it was enough to see how the STFT and LTFT should behave and also monitor the fuel rail pressure. Lessons learned: (1) stick with the more expensive MAF (2) change the fuel pressure sensor early in the troubleshooting process especially since the Bosch unit was about $50, easy to change and it is a critical input into the engine operation (3) spend the money on an OBDII scan tool that connects to a smartphone or your laptop via Bluetooth or WiFi. The Bluetooth works well although I read that other owners have had some challenges with Bluetooth (4) get a baseline set of logs for your car when things are in working order - i.e. so you know what is different. Lastly, thanks to everyone contributing to these logs. I am going to share my experience with my Volvo mechanic - this will save his valuable time as he is a one-man operation and headaches like this consume time that we need him to focus on other problems and avoids the dreaded trip to the dealership.

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