DTC P0171 System Too Lean
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BMW Technical Information System
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This Diagnostic Trouble Code (DTC P0171) relates to the adaptive capability of the Powertrain Control Module (PCM). This stored Diagnostic Trouble Code (DTC P0171) is not definitive enough to just replace the parts based upon its’ indication.
This DTC P0171 is saying that the engine is running too lean and has reached the limits of its’ adaptive ability to control the fuel mixture to the ratio of 14.7:1 (parts air to fuel). The Powertrain Control Module (PCM) uses the feedback signal from the pre-catalyst Heated Oxygen Sensors (HO2S) to add or subtract fuel to the engine by manipulating the injector pulse width.
The Powertrain Control Module (PCM) adjusts the mixture in controlled steps. These steps are Short Term fuel trim and Long Term Fuel Trim. As their names imply the Short Term Fuel Trim is incrementally adjusted within a Long Term Fuel Trim cell. These values are typically displayed as a percentage of positive or negative adjustment.
A Scan Tool such as our 2x80 series scan tool with a good software package can be used to view the data from the Powertrain Control Module (PCM).
To perform the job correctly you should look at the items that could have caused the reported DTC. This would include an inspection of the basic items such as cracked exhaust manifold, vacuum leaks, stopped up injectors, contaminated fuel, stopped up fuel filter, bad fuel pressure regulator, and failing fuel pump. A misfiring engine can also cause this problem, so if you have any DTC P03xx codes check and repair them first.
You should check for Technical Service Bulletins (TSB) including those that address the possible need to reprogram the Powertrain Control Module (PCM) that may relate to the Diagnostic Trouble Code (DTC P0171). If it needs reprogrammed that can be performed with J2534 tools such as ours.
Fix It Right The First Time!
Fortunately, everything you need everything you need to fix it right the first time is right here!
To access the sensor and data from your Engine Controller (PCM) you will need:
Professional Quality Scan Tool such as our 2X80S Scan Tool series.
Professional Quality Automotive Diagnostic Software such as OBD2 Spy, OBD 2007, or Scan Master.
If you understand how the systems were designed to work and how to test them, great! Otherwise you will need factory product service training manuals that will teach you and guide you through the diagnostic phase.
You might also need the manufacturer factory service manuals and data systems that provide specifications and details relative to your specific model.
Or aftermarket data systems such as All Data, Mitchell On Demand, Auto Data, Bosch, and others.
Everything is available here for you as a single source for all your needs. The aftermarket data systems are available in our members only area by direct shipment from the distributor at great pricing.
