Description
OBD-II Trouble Code Description for P0157 BMW
O2 Sensor Circuit Low Voltage
What does this mean?
OBD2 Code P0157 BMW definition:
This code definition:a fault in the post-catalyst o2 sensor on Bank 2. First, a basic run-down of the catalyst: The Catalytic Converter is used to help control tailpipe emissions, to “clean up” the exhaust, if you will. The PCM (Powertrain Control Module) uses the signal from the heated oxygen sensor to the rear of the catalyst to monitor the catalyst’s efficiency by comparing it to the o2 sensors in front of the catalyst. If the PCM sees little or no difference between the exhaust quality in post- and pre- catalyst sensors then it knows that the catalyst is not working properly. To over simplify: a post-cat sensor’s main job is to monitor catalyst efficiency, not control fuel management (although they can have a measure of influence over the front o2 sensor’s operation, we’ll just stick to basics for the sake of simplicity). If you have a P0157 BMW, that doesn’t mean your catalyst is bad (in fact, it usually never does). This code basically means that the Bank 2, Sensor 2 (or second o2 sensor back on bank 2) signal voltage is below what is considered normal for that sensor. It’s a four wire sensor being supplied a 0.5 volt reference voltage (usually on the signal wire) and a ground, as well as a power and ground circuit for the o2 sensor heater element. Changes in oxygen content cause resistance changes in the sensor’s signal circuit. This changing resistance affects the 0.5 volts on the signal/reference circuit. A heated o2 sensor is capable of switching between 0.1 volts and 0.9 volts. However, a properly working post-catalyst sensor will exhibit small changes at a slower rate than front (pre-catalyst) o2 sensors. It may switch slightly above and below 0.45 volts at the rate of about 1 switch per second or less(depends on the vehicle). The PCM monitors this changing signal to determine if the catalyst is working properly. If the PCM determines that the post-cat o2 sensor signal voltage is below a certain threshold for too long, P0157 BMW will set.
Symptoms
Possible sumptoms of OBD code P0157 BMW
Usually rear o2 sensor problems won’t cause drivability issues since they are an input that measures catalyst efficiency (unlike front o2 sensors). However if you have other codes present, like lean codes or pre-o2 sensor codes, then they may cause drivability problems as well as P0143 BMW. The following symptoms may be present: MIL (Malfunction Indicator Lamp) illumination Engine performance issues Engine running rough Engine running rich (only if PCM is trying to add fuel to compensate for low o2 sensor voltage reading) Engine running lean (only if vacuum leak is large enough that PCM can’t compensate by adding fuel) Poor idle
Causes
Possible causes of OBD code P0157 BMW
If you have reason to believe that your engine is running lean, fix that problem first, then clear codes and see if the P0157 BMW code resets. An engine that is running lean could set this code, but usually there will be lean codes (P0171 BMW, P0174 BMW) present. The following could be causes: Air leaks in exhaust in front of o2 sensor giving false reading Engine running excessively lean O2 sensor connector damaged/corroded O2 sensor signal circuit is shorted to ground O2 sensor ground circuit is open O2 sensor has failed (it may be contaminated with fuel or coolant) PCM has failed
Possible Solutions
It’s always good to start with checking for air leaks in the exhaust manifold and in the exhaust pipes. Fix these first. With KOER (Key on engine running) use a scan tool or a voltmeter check the o2 sensor signal voltage with engine warm. You may have to increase the RPM to a fast idle to check the voltage of the bank 2,2 sensor. If it’s voltage is stuck low (less than 0.5 volts may not be enough to set the code, but it depends on the vehicle) and you don’t have any other o2 sensor codes present in the PCM, then it’s a good bet that the sensor is bad. If the voltage isn’t stuck low and the o2 sensor seems to be operating fine, it’s likely sticking low intermittently. This often turns out to be the sensor. In either case, replacing the sensor can be an effective way to diagnose the problem. But it can also be an expensive diagnostic tool, especially if it turns out to be a wiring issue, instead of a sensor. So, if you’re interested in knowing for sure what the problem is before spending unnecessarily, then perform the following: 1. Turn off the engine and unplug the 2,2 o2 sensor connector. Inspect for corrosion, etc. Repair as necessary. Make sure that there is battery voltage present and ground present for the o2 sensor heater. If there isn’t, then diagnose that first then retest. The o2 sensor depends on the heater to warm it up so it can start working quicker. If the heater element is bad or there isn’t the proper voltage supplying it, the sensor may set this code. Usually heater problems have codes associated with them, too. If you find there is no battery voltage feeding the o2 sensor use the associated code to diagnose that. If you find the heater element bad, replace the sensor. If the heater element checks out then, using a jumper wire, supply a chassis ground to the o2 sensor connector(PCM side) ground circuit. Now observe the scan tool bank 2,2 o2 sensor reading. If it is now at about a half a volt then replace the o2 sensor. If, after supplying a ground to the unplugged PCM side of the o2 sensor connector, the voltage reading doesn’t change then check the harness for short to ground. Check for harness making contact with exhaust components. Check pins for damage, and for moisture. Repair as necessary. If you can find no harness problems, then the PCM may be at fault.
The OBD2 Code Information Be Applicable For BMW:
2013 BMW X6 M50d,2013 BMW X6,2013 BMW X5 eDrive Concept,2013 BMW X5 Security Plus Concept,2013 BMW X5 M50d,2013 BMW X4 Concept,2013 BMW X1,2013 BMW Pininfarina Gran Lusso Coupe,2013 BMW M6 Coupe US-Version,2013 BMW M6 Coupe,2013 BMW M6 Convertible,2013 BMW M5 US-Version,2013 BMW M550d xDrive Touring,2013 BMW M550d xDrive,2013 BMW M4 Coupe Concept,2013 BMW M135i,2013 BMW Active Tourer Outdoor Concept,2013 BMW 7 ActiveHybrid,2013 BMW 750Li,2013 BMW 7-Series,2013 BMW 640i Gran Coupe,2013 BMW 640d xDrive Coupe,2013 BMW 6-Series Gran Coupe UK Version,2013 BMW 6-Series Gran Coupe,2013 BMW 5 ActiveHybrid,2013 BMW 4-Series Coupe Concept,2013 BMW 3 ActiveHybrid,2013 BMW 3-Series Touring,2013 BMW 3-Series Long Wheelbase,2013 BMW 1-Series 3-door,2012 BMW i8 Spyder Concept,2012 BMW i3 Coupe Concept,2012 BMW Zagato Roadster Concept,2012 BMW Zagato Coupe Concept,2012 BMW M5 UK Version,2012 BMW M5,2012 BMW M3 DTM Champion Edition,2012 BMW M3 CRT,2012 BMW M135i Concept,2012 BMW Active Tourer Concept,2012 BMW 650i Convertible,2012 BMW 640d Coupe,2012 BMW 6-Series Coupe,2012 BMW 6-Series Convertible,2012 BMW 3-Series,2012 BMW 1-Series Urban Line,2012 BMW 1-Series Sport Line,2012 BMW 1-Series Coupe,2012 BMW 1-Series Convertible,2012 BMW 1-Series,2011 BMW i8 Concept,2011 BMW i3 Concept,2011 BMW Z4,2011 BMW X5,2011 BMW X3 xDrive35i,2011 BMW X3 xDrive20d,2011 BMW X3,2011 BMW X1 xDrive28i,2011 BMW M5 Concept,2011 BMW M3 Pickup Concept,2011 BMW M3 GTS,2011 BMW M3 Frozen Gray,2011 BMW ConnectedDrive Concept,2011 BMW ActiveE Concept,2011 BMW 750Li,2011 BMW 5-Series Touring,2011 BMW 5-Series Long-Wheelbase,2011 BMW 5-Series,2011 BMW 335is Coupe,2011 BMW 328 Hommage Concept,2011 BMW 3-Series Coupe,2011 BMW 3-Series Convertible,2011 BMW 1-Series M Coupe US Version,2011 BMW 1-Series M Coupe UK Version,2011 BMW 1-Series M Coupe MotoGP Safety Car,2011 BMW 1-Series M Coupe,2010 BMW Z4 UK Version,2010 BMW Z4 GT3,2010 BMW Z4,2010 BMW X6 M,2010 BMW X6 ActiveHybrid,2010 BMW X5 M,2010 BMW X1,2010 BMW Scooter C Concept,2010 BMW M3,2010 BMW Gran Coupe Concept,2010 BMW ActiveE Concept,2010 BMW 7 ActiveHybrid,2010 BMW 760Li,2010 BMW 7-Series High Security,2010 BMW 6-Series Coupe Concept,2010 BMW 5-Series Gran Turismo,2010 BMW 5-Series ActiveHybrid Concept,2010 BMW 320d EfficientDynamics,2010 BMW 135i Coupe,2010 BMW 135i Convertible,2009 BMW X6 UK Version,2009 BMW X6,2009 BMW X5 xDrive35d BluePerformance,2009 BMW X5 Security Plus,2009 BMW X5 Security,2009 BMW X3 Limited Sport Edition,2009 BMW M3 Saloon UK Version,2009 BMW M3 Race Version,2009 BMW M3 Convertible UK Version,2009 BMW M3 Convertible,2009 BMW EfficientDynamics Concept,2009 BMW 750Li,2009 BMW 730d,2009 BMW 7-Series UK Version,2009 BMW 7-Series,2009 BMW 5-Series Gran Turismo Concept,2009 BMW 335d BluePerformance,2009 BMW 3-Series UK Version,2009 BMW 3-Series Touring UK Version,2009 BMW 3-Series Touring,2009 BMW 3-Series,2009 BMW 1-Series Convertible UK Version,2008 BMW X5 M-Package,2008 BMW X1 Concept,2008 BMW M5 Touring,2008 BMW M3 Sedan US-Version,2008 BMW M3 Sedan,2008 BMW M3 Coupe US-Version,2008 BMW M3 Coupe UK Version,2008 BMW M3 Coupe,2008 BMW M1 Concept,2008 BMW M-Zero Concept,2008 BMW GINA Light Visionary Model Concept,2008 BMW EfficientDynamics Concept,2008 BMW Coupe Range,2008 BMW 7-Series ActiveHybrid Concept,2008 BMW 650i Convertible,2008 BMW 635d Coupe,2008 BMW 530i,2008 BMW 5-Series Touring,2008 BMW 5-Series Security,2008 BMW 5-Series,2008 BMW 135i Coupe,2008 BMW 128i Convertible,2008 BMW 1-Series Range,2008 BMW 1-Series Coupe,2008 BMW 1-Series Cabrio,2008 BMW 1-Series 5-door,2008 BMW 1-Series 3-door,2007 BMW X6 Concept,2007 BMW X6 ActiveHybrid Concept,2007 BMW X5 4.8i,2007 BMW X5 3.0d,2007 BMW X3,2007 BMW M6 Convertible Neiman Marcus,2007 BMW M6 Cabrio,2007 BMW M5,2007 BMW M3 Concept,2007 BMW Hydrogen 7,2007 BMW Concept CS,2007 BMW 530Li,2007 BMW 335i Coupe,2007 BMW 335i Convertible,2007 BMW 1-Series tii Concept,2006 BMW Z4 Roadster,2006 BMW Z4 M Roadster,2006 BMW Z4 M Coupe UK version,2006 BMW Z4 M Coupe,2006 BMW Z4 Coupe,2006 BMW Mille Miglia Coupe Concept,2006 BMW Art Car Collection,2006 BMW 7 Series High Security,2006 BMW 760Li,2006 BMW 750i,2006 BMW 750Li with Shadow Line,2006 BMW 750Li,2006 BMW 330i,2006 BMW 325i Touring,2006 BMW 320si E90 WTCC,2006 BMW 320si,2006 BMW 320d Touring,2006 BMW 320d,2005 BMW Z4 Coupe Concept,2005 BMW X5,2005 BMW X3 EfficientDynamics Concept,2005 BMW X3,2005 BMW M6,2005 BMW M5,2005 BMW H2R,2005 BMW 630i,2005 BMW 545i Touring,2005 BMW 530xi Touring,2005 BMW 530xi,2005 BMW 530d Touring,2005 BMW 330i M-Package,2005 BMW 320d Touring,2005 BMW 130i M-Package,2005 BMW 130i,2005 BMW 120i UK Version,2005 BMW 120i,2005 BMW 120d,2004 BMW X5 4.8is,2004 BMW X5 4.4i,2004 BMW X3 3.0i,2004 BMW X3 2.0d,2004 BMW H2R Hydrogen Racecar,2004 BMW Concept M5,2004 BMW 645Ci Convertible,2004 BMW 645Ci,2004 BMW 5 Series,2004 BMW 530i,2004 BMW 530d,2004 BMW 330Ci Coupe,2004 BMW 330Ci Convertible,2004 BMW 330Cd Coupe,2004 BMW 325Ci Coupe,2004 BMW 320Cd Convertible,2004 BMW 318Ci Convertible,2003 BMW Z4 2.5i,2003 BMW Z4,2003 BMW M3 CSL,2003 BMW 760Li E66,2003 BMW 325ti Compact,2003 BMW 3-Series Compact,2002 BMW xActivity Concept,2002 BMW X5 4.6is,2002 BMW CS1 Concept,2002 BMW 7 Series,2002 BMW 760i,2002 BMW 760Li Yachtline Concept,2002 BMW 740d,2002 BMW 730d,2002 BMW 3-Series Touring,2002 BMW 3-Series,2001 BMW Z8
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