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Pelican Technical Article:

Reading Fault Codes

Nick Czerula

Time:

1 hours1 hrs

Talent:

**

Tools:

Scan tool, Code reader

Applicable Models:

BMW E90 3-Series (2006-07)
BMW E91 3-Series (2006-07)
BMW E92 3-Series (2007)
BMW E93 3-Series (2007)

Parts Required:

Code reader

Hot Tip:

Start with a fully charger batter

Performance Gain:

Repair fault codes

Complementary Modification:

Do not clear fault codes until you think you have repaired the problem

The impetus to control motor vehicle emissions, driven by the air quality needs of major metropolitan areas, has lead to 5 decades of engineering innovation in the design of vehicle propulsion technologies. Because California cities (particularly Los Angeles) were hardest hit by the proliferation of vehicles and their emissions, starting in 1961 the California Air Resources Board (CARB) has been at the forefront of setting engineering standards for vehicles sold in California, then in the United States and now for the world automotive industry.

Modern vehicle engine operations and emissions (including evaporative losses from the fuel tank) are extensively controlled via a digital microprocessor, the computer known as the engine control module or ECM. Feedback systems, relying on sensors, allow the ECM to precisely control fuel / air mixture, spark timing and other functions. Of the many sensors on the engine and the vehicle, the primary ones are oxygen sensor(s) which monitor the combustion efficiency of the engine, and knock sensor(s) which "listen" for engine knock or pinging. The input signals from these sensors are used by the ECM to adjust fuel mixture and adjust spark timing.

Computer control of the engine operations allow two benefits in addition to a precise air fuel mixture and, therefore, lower emissions. The computers can be programmed to detect faults (diagnostic trouble codes or DTCs) in their own operations, and the ECM can store this information and illuminate a malfunction indicator light (MIL), often called the Check Engine light or malfunction Indicator lamp, on the instrument cluster. The stored faults can be viewed later for diagnosis and repair.

Diagnosis of modern vehicle performance faults start with gaining access to DTCs stored in the ECM. Start by looking for the 16-pin OBD II plug (diagnostic link connector or DLC) under the dashboard. By law, it is always located within reach of the driver.

Once the diagnostic scan tool is connected to the DLC, follow instructions on the scan tool screen. These usually include:

• Select diagnosis program.

• Select correct vehicle (scan tool should find this automatically).

• Interrogate and record DTCs (fault codes) present in ECM memory.

In many cases, it is best to clear DTCs, then drive the vehicle and retest. Follow diagnostic and repair instructions on scan tool screen. DTCs for the vehicle power train, as standardized by the American Society of Engineers (ASE), begin with a P and are followed by 4 digits. (They are also referred to as P-codes.) During testing, the scan tool displays each P-code and a brief description of the fault. There are different kinds of fault indicated by DTCs:

• Plausibility. If a sensor's output value is outside the expected range, the signal from the sensor is considered not plausible and a fault is set.

• Power, ground, continuity. If power or ground is missing or continuity is lacking in a particular circuit or system, a fault is set.

• Fault in sensor or module. If a sensor or module tests defective, a fault is set.

You should note that even though the scan tool displays specific DTCs, additional diagnosis is advisable. For example, if a DTC indicates a non-functional oxygen sensor heater, the simple explanation may be a blown fuse. In other words, use common sense and do not ignore the obvious when diagnosing problems.

BMW E90 models have one of the most complicated BMW electrical systems to date. When addressing fault codes it is important t keep this in mind. There are many control modules that now share the control of a single function. For example, the fuel pump is controlled by the DME, with the signal traveling through the E-box to the fuel pump control module. BMW calls this type of system distributed functions. This is where a more advanced BMW scan tool is needed to completely diagnose some fault codes your BMW may set. Do not be discouraged from attempting to diagnose fault codes on your own, just know there will limits to how far you can go. As stated above, the engine management system monitors emission components and will set a fault code in the DME when a fault is present. These are the codes you will have to work with the most. Treat them as you normally would and inspect the component and system the fault code relates to. If you find a code will not clear or points to a system, your scan tool cannot access, you may need a more advanced scan tool. Know your scan tool and the limits it is designed with and use all available resource to help during your diagnosis.

Connecting a Scan Tool

Working at the driver side kick panel, remove the OBD II connector access door.
Figure 1

Working at the driver side kick panel, remove the OBD II connector access door. (green arrow)

With the access door removed, pull the OBD II connector cover off.
Figure 2

With the access door removed, pull the OBD II connector cover off. (green arrow)

Plug your scan tool into the OBD II connector.
Figure 3

Plug your scan tool into the OBD II connector.

Follow directions supplied with scan tool to interrogate ECM fault memory.
Figure 4

Follow directions supplied with scan tool to interrogate ECM fault memory. Read fault code, diagnose problem, then clear fault code when complete.

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Comments and Suggestions:
bmwguy Comments: I mean that the car is letting off a little to much fume than it should.
December 9, 2013
  Followup from the Pelican Staff: It's possible the coding was changed when the mileage was corrected, but unlikely. I would start by checking the DME for fault codes. If the system is not working properly, a fault code will be set. This will be your best bet when diagnosing.
- Nick at Pelican Parts
 
bmwguy Comments: Thank you for the advice also I took the car to the garage and they checked the fumes merchanic said the car is running very fine on fuel as the fumes were very rich... Can the mileage correction lead to problems such as these?
December 7, 2013
  Followup from the Pelican Staff: I don't understand this: "car is running very fine on fuel" and "fumes were very rich" are contradictory. Or are you saying that the fuel mileage is now ok?- Nick at Pelican Parts  
bmwguy Comments: I had my mileage corrected on my 2009 bmw 3 series his has lead to the car dropping from around 37 mpg to 20 mpg and the car letting off to much emunision can any1 help me. when they corrected my mileage they took out the clock light module and did something to the key.
December 6, 2013
  Followup from the Pelican Staff: I would start by checking the DME for fault codes. If the system is not working properly, a fault code will be set. This will be your best bet when diagnosing. - Nick at Pelican Parts  
mohd Comments: Hi

My HPFP reachs 125000 hp and I did not feel low power when I drive normal but once kickdown almost 30ff code appears low turbo chatger pressure
October 23, 2013
  Followup from the Pelican Staff: Check all of the vacuum lines for the turo system, make sure none of them are leaking, or broken.
- Nick at Pelican Parts
 
mohd Comments: Hi

50000 hpa only during warming or start butt when I drive it increases gradually. ... by the way, when I try accelerate quickly throw kickdown. , 30ff fault appears immediately alone and sometimes comes with 2aaf

Rarely 2aaf comes alone

Please advise

October 18, 2013
  Followup from the Pelican Staff: It sounds to me like you are having a problem with the high pressure fuel pump. Does the car see to misfire at idle or be low on power?
- Nick at Pelican Parts
 
mohd Comments: I got the readings once started. Rpm about 1000 during warmingm
October 17, 2013
  Followup from the Pelican Staff: The HPP on your car should max out at 125 bar witch is 125000 hpa, measuring this much fuel pressure is only possible with the test plan in the factory scan tool. 50000 hps is on the low side, is your car misfiring at idle, and low on power?
- Nick at Pelican Parts
 
mohd Comments: My car reading regarding fuel pump high pressure is 50000 hpa and for mass air flow is 13 kg/h
Is it ok???
October 16, 2013
  Followup from the Pelican Staff: When are these readings recorded? Engine conditions, for example, RPM, cranking, warm, etc. - Nick at Pelican Parts  
mohd Comments: Hi,
BMW 335i e93 2009

what is the range of high and low pressure fuel pump in hpa ?
what is the range of mass air flow in kg/hr??


October 15, 2013
  Followup from the Pelican Staff: The low pressure pump will run at 5 bar when commanded on with the scan tool.

The remainder of your requested data is built into BMW scan tools and part of a test plan. It is not available in repair manuals.

- Nick at Pelican Parts
 

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Page last updated: Thu 9/18/2014 01:15:37 AM