DTC Troubleshooting

P0171, P0172 DIAGNOSIS PROCEDURE

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:J24B .
2	DTC check Check DTC. Is there DTC(s) other than P0171 and P0172?	Go to applicable DTC (s).	Go to Step 3.
3	Exhaust system and air intake system check Check exhaust system and air intake system for clogging or leak. Is it in good condition?	Go to Step 4.	Repair or replace defective parts.
4	Fuel system check Check fuel system, see FUEL SYSTEM INSPECTION . Is it in good condition?	Go to Step 5.	Repair or replace defective parts or wire harness.
5	MAF sensor performance check Turn OFF ignition switch and connect scan tool to DLC. Start engine and warm up to normal operating temperature. Check MAF value using scan tool. (Refer to SCAN TOOL DATA:J24B for normal value.) Is normal value indicated?	Go to Step 6.	Repair or replace defective parts or wire harness.
6	ECT sensor circuit check Check ECT sensor circuit referring to Step 3 of DTC P0116/P0125/P0128 . Are they in good condition?	Go to Step 7.	Repair or replace defective wire harness.
7	ECT sensor check Check ECT sensor, see ECT (ENGINE COOLANT TEMPERATURE) SENSOR INSPECTION . Is it in good condition?	Go to Step 8.	Replace ECT sensor.
8	DTC recheck Replace A/F sensor, see A/F (AIR FUEL RATIO) SENSOR, HO2S (HEATED OXYGEN SENSOR) REMOVAL AND INSTALLATION . Perform DTC confirmation procedure and check DTC. Is DTC P0171 or P0172 still detected?	Substitute a known-good ECM and recheck.	End.