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Re: Hello, took my car for emissions test and fail with...
Well go back and ask for proper print out of what the emmisions readings are ,i cannot beleave that a vehicle test station can fail a vehicle and not tell you what the emmisions readings are but give you a lot of useless p numbers ,dont they put a probe up the exhaust and test it properly ,They would have field day trying to test europeon cars here in europe with all the encrypted software used on vehicles here and the vehicle shutting its self down with the immobilisor and throwing out code p whatever for illegal access to the ECU.any way try changing the lambada sensors as i think that this is what code P171 and 174 refer too
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• DTC P0171 Fuel Trim System Lean Bank 1
• DTC P0174 Fuel Trim System Lean Bank 2
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The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop, the ECM determines fuel delivery based on sensor signals without oxygen sensor (O2S) input. During Closed Loop, the O2S inputs are added and used by the ECM to calculate short and long term fuel trim (FT) fuel delivery adjustments. If the O2S indicates a lean condition, FT values will be above 0 percent. If the O2S indicate a rich condition, FT values will be below 0 percent. Short term FT values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long term FT makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. If the ECM detects an excessively lean condition, DTC P0171 or P0174 sets.
Diagnostic Aids
• Excessive resistance in the fuel injector ignition 1 voltage circuit or the fuel injector control circuit may cause the following symptoms:
- Lean condition
- Misfire
- Rough idle
• The system will go lean if an injector is not suppling enough fuel.
• A lean condition could be present during high fuel demand.
• A malfunctioning MAF sensor can cause this DTC to set. Refer to DTC P0101 .
• Review the Failure Records with a scan. If an intermittent condition is suspected, refer to Intermittent Conditions .
DTC Descriptors
This diagnostic procedure supports the following DTCs:
• DTC P0420 Catalyst System Low Efficiency Bank 1
• DTC P0430 Catalyst System Low Efficiency Bank 2
This code could mean the catalytic converter on that bank has failed .
PO171 System too Lean Bank
P0174 Fuel Injection System Too Lean Bank 2
If the P0171 is combined with the P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replaced the air filter and clean the air flow meter. If the problem persist the front oxygen (O2) sensor may need to be replaced.
code p0101 refers to MAF sensor and VAF sensor--range /performance problems===causes --intake leakage/blockage ---MAF/VAF sensor failure.
code p0300 refers to random misfires multiple cylinders ---causes --spark plugs /HT leads --injector /s-- ignition coil/ s--low compression ---wiring
check fuel pressure in manifold and HT leads
code p0171 refers to system too lean bank 1 ===causes --intake /exhaust air leak---AIR system---MAF/VAF sensors ---fuel pressure /pump---injectors ---HO2S sensor
Basically there are two codes referring to the MAF/VAF sensors so check them out and two codes referring to fuel pressure and pump so have a pressure test done on the fuel manifold to determine if pump or pressure regulator.
Diagnostic Test Code (DTC) P0171 and P0174 are both "LEAN OXYGEN SENSOR" codes. One is for one side of the engine and the other is for the other side of the engine.
To put it simply, you have too much oxygen in your exhaust on BOTH sides of the engine at the same time.
This can be caused by a number of things including vacuum leaks, low fuel pressure, or a bad Manifold Absolute Pressure (MAP) sensor or Mass Air Flow (MAF) sensor.
This should be diagnosed using a scan tool that can read fuel trim data so that an effective repair can be made and verified.
Please note that it is HIGHLY UNLIKELY that these codes are being caused by the oxygen sensors themselves.
Would start with the mass air flow sensor the other two codes may have been triggered by the performance of the MAF sensor. Is the vehicle running poorly or have high or low idle?
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