P0171
DTC P0171The catalyst's efficiency is demonstrated by its ability to oxidize CO and hydrocarbon emissions. The ECM/PCM compares the output signals of the front and rear oxygen sensors to determine whether the output of the rear sensor is beginning to match the output of the front oxygen sensor. Air/fuel mixture compensation keeps the frequency of the front oxygen sensor high due to the changes from rich-to-lean combustion. The catalyst causes the rear oxygen sensor to have a lower frequency. As the catalyst wears, the rear oxygen sensor's signal trace begins to match the front oxygen sensor's signal trace. That is because the catalyst becomes saturated with oxygen and cannot use the oxygen to convert hydrocarbon and CO into H2O and CO2 with the same efficiency as when it was new. A completely worn catalyst shows a 100% match between the frequency of the front and rear sensors.
DTC DESCRIPTION
If the correction value of air-fuel ratio is higher than the threshold value, ECM/PCM sets DTC P0171.
DTC Detecting Condition:
MONITOR SCANTOOL DATA
1. Connect scantool to Data Link Connector(DLC).
2. Warm up the engine to normal operating temperature.
3. Monitor the "Parameters related to air/fuel ratio(HO2S, MAF, MAP, TPS, ECTS, PCSV, Injector, etc.)" on the scantool.
4. Are the parameters displayed correctly?
YES - Fault is intermittent caused by poor contact in the sensor's and/or ECM's connector or weather proofed and ECM/PCM memory was not cleared. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of vehicle Repair" procedure.
NO - Go to "Terminal and Connector Inspection" procedure
TERMINAL AND CONNECTOR INSPECTION
1. Many malfunctions in the electrical system are caused by poor harness and terminals. Faults can also be caused by interference from other electrical systems, and mechanical or chemical damage.
2. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage.
3. Has a problem been found?
YES - Repair as necessary and go to "Verification of vehicle Repair" procedure.
NO - Go to "System inspection" procedure.
SYSTEM INSPECTION
1. Air leakage check.
a. Check "Air intake system"
- Check looseness, deterioration or contamination on throttle body and gasket.
- Check contamination, damage or crack on intake manifold, ISCA and injectors.
b. Is there any leakage?
YES - Repair as necessary and go to "Verification of vehicle Repair" procedure
NO - Go to "Fuel line check" procedure.
2. Fuel line check.
a. Check "Fuel line system"
- Check looseness of connectors on fuel line.
- Check looseness, damage, or interference of vacuum hose on fuel line.
- Check damage, leakage or bending on fuel line pipe.
b. Is fuel line normal?
YES - Go to "Fuel line pressure check" procedure.
NO - Repair as necessary and go to "Verification of vehicle Repair" procedure.
3. Fuel line pressure check.
a. Key "OFF".
b. Remove fuel pump relay.
c. Engine start and wait until engine stop. and then key "OFF".
d. Install a fuel pump relay.
e. Connect fuel pressure gauge using the correct adapter.
f. Start the engine, and record fuel pressure.
Specification : Approx. 3.5 kgf/sq.cm (343.2 kPa, 50psi)
g. Is the fuel pressure normal?
YES - Go to "Component inspection" procedure.
NO
- Check clogging on the fuel filter.
- Check the supply pressure of fuel pump.
- Repair as necessary and go to "Verification of vehicle Repair" procedure.
COMPONENT INSPECTION
1. PCV(Positive Crankcase Ventilation) valve check.
a. Key "OFF".
b. Disconnect PCV valve.
c. Check PCV plunger movement.
d. Is the movement of plunger normal?
YES - Go to "PCSV check" procedure.
NO
- Substitute with a known - good PCV valve and check for proper operation.
- If the problem is corrected, replace PCV valve and go to "Verification of Vehicle Repair" procedure.
2. PCSV check.
a. Key "OFF".
b. Disconnect PCSV and vacuum hose.
c. Apply a vacuum by a hand vacuum gauge on PCSV.
d. Does PCSV keep the vacuum condition normally?
YES - Go to "Injector check" procedure.
NO
- Substitute with a known - good PCSV and check for proper operation.
- If the problem is corrected, replace PCSV and go to "Verification of Vehicle Repair" procedure.
3. Injector check.
a. Key "OFF".
b. Disconnect injectors.
c. Check clog on injectors.
d. Measure the resistance between terminal 1 and 2 of injectors(Component side).
Specification :
Temperature Resistance (ohms)
20 °C (68 °F) 13.8 - 15.2 ohms
e. Is the measured resistance within specifications?
YES - Go to "Sensors related to air/fuel ratio check" procedure.
NO - Repair or replace as necessary. And then, go to "Verification of Vehicle Repair" procedure.
4. Sensors related to air/fuel ratio check.
a. Check the output data of sensors related to air/fuel ratio (HO2S, MAPS, TPS, ECTS, PCSV, Injectors, etc.) on scantool. (Refer to each DTC guide procedure.)
b. Are those sensors normal?
YES
- Substitute with a known - good ECM/PCM and check for proper operation.
- If the problem is corrected, replace ECM/PCM and go to "Verification of Vehicle Repair" procedure.
NO - Repair or replace as necessary. And then, go to "Verification of Vehicle Repair" procedure.
VERIFICATION OF VEHICLE REPAIR
After a repair, it is essential to verify that the fault has been corrected.
1. Connect scan tool and select "Diagnostic Trouble Codes(DTCs)" mode.
2. Clear the DTCs and Operate the vehicle within DTC Enable conditions in General information.
3. Are any DTCs present ?
YES - Go to the applicable troubleshooting procedure.
NO - System is performing to specification at this time.