DTC P0171 / P0172

DTC Detecting Condition and Trouble Area

DTC detecting condition	Trouble area
P0171: System Too Lean Fuel trim correction is higher than specified value for specified time under specified vehicle condition. (3 D/C detection logic)	•Fuel system •Air intake system •Exhaust system •HO2S-1 and/or its circuit •Emission control system •ECM
P0172: System Too Rich Fuel trim correction is lower than specified value for specified time under specified vehicle condition. (3 D/C detection logic)

Circuit Diagram

[A]:	ECM connector (View: [a])	B1:	HO2S-2 heater power supply circuit	2.	HO2S-2
A1:	HO2S-1 heater power supply circuit	B2:	HO2S-2 signal circuit	3.	ECM
A2:	HO2S-1 signal circuit	B3:	HO2S-2 ground circuit	4.	Shield wire
A3:	HO2S-1 ground circuit	B4:	HO2S-2 heater drive circuit
A4:	HO2S-1 heater drive circuit	1.	HO2S-1

DTC Confirmation Procedure

WARNING:

If you do not select a suitable route and take proper precautions when performing a road test, an accident can occur.

•Select a level road with no traffic to minimize the risk of accident.
•Perform the test extremely carefully.
•Perform the road test with 2 persons, a driver and a tester.

NOTE:

•Check that the following conditions are met in this “DTC Confirmation Procedure”.

—A/F feedback (closed loop) control is activated.
—ECT > 70 °C (158 °F)
—IAT ≤ 75 °C (167 °F)

•Check that the following DTCs are not detected in this “DTC Confirmation Procedure”.

—IAT sensor (P0112 and P0113)
—ECT sensor (P0116, P0117 and P0118)
—EVAP canister purge valve (P0443, P0458 and P0459)

1)Warm up engine to normal operating temperature.

2)Drive vehicle at 50 to 80 km/h (31 to 50 mile/h) constantly for 10 min. or more.

DTC Troubleshooting

Step	Action	Yes	No
1	Was “Engine and Emission Control System Check” performed?	Go to Step 2.	Go to Engine and Emission Control System Check:M16A.
2	DTC check Is there any DTC(s) other than P0171 and P0172?	Go to troubleshooting for applicable DTC.	Go to Step 3.
3	Fuel system and emission control system check 1)Check the following points related to fuel and emission control systems. •Fuel pressure: •Fuel injector circuit: •Fuel injector: •MAP sensor: •EVAP canister purge valve: •PCV valve: Is check result OK?	Go to Step 4.	Repair or replace defective parts.
4	Exhaust system and air intake system check 1)Check exhaust system and air intake system for clogging or leakage. Is check result OK?	Go to Step 5.	Repair or replace defective part.
5	HO2S-1 signal circuit check 1)Check HO2S-1 signal circuits according to Step 3 under DTC P0131 / P0132:M16A. Is check result OK?	Go to Step 6.	Repair or replace defective wire harness.
6	DTC recheck 1)Replace HO2S-1. 2)Perform “DTC Confirmation Procedure” and check DTC. Is DTC P0171 or P0172 still detected?	Replace ECM and recheck DTC.	End.