6-82 ENGINE GENERAL INFORMATION AND DIAGNOSIS (G16/J20 ENGINES)
DTC P0171 Fuel System Too Lean
DTC P0172 Fuel System Too Rich
SYSTEM DIAGRAM
Refer to “Electronic Control System Description” in Section 6E1.
DTC DETECTING CONDITION AND TROUBLE AREA
DTC CONFIRMATION PROCEDURE
1) Connect scan tool to DLC with ignition switch OFF.
2) Turn ON ignition switch and clear DTC, pending DTC and freeze frame data by using scan tool and warm up
engine completely.
3) Increase vehicle speed to 50 – 60 km/h (30 – 40 mph).
4) Keep driving above vehicle speed for 3 min. or more.
5) Stop vehicle and check DTC and pending DTC by using scan tool.
DTC DETECTING CONDITION TROUBLE AREA
When running after engine warmed
• Short term fuel trim exceeding 15% or long term fuel trim
exceeding 20% and total trim exceeding 43% is detected.
– Fuel system too lean
• Short term fuel trim less than –11% or long term fuel trim
less than –11% and total trim less than –30% is detected.
– Fuel trim too rich
(2 driving cycles detection logic)
• Vacuum leaks (air inhaling)
• Exhaust gas leakage
• Fuel pressure out of specification
• Heated oxygen sensor malfunction
• EGR system malfunction
• MAF sensor poor performance
• ECT sensor poor performance
• Fuel level sensor
WARNING:
• When performing a road test, select a place where there is no traffic or possibility of a traffic acci-
dent and be very careful during testing to avoid occurrence of an accident.
• Road test should be carried out with 2 persons, a driver and a tester, on a level road.
NOTE:
Check to make sure that the following conditions are satisfied when using this “DTC Confirmation
Procedure”.
• Intake air temp. at start : –8 – 60°C (18 – 140°F)
• Engine coolant temp. at start : –8 – 95°C (18 – 203°F)
• Altitude (barometric pressure) : 2400 m, 8000 ft or less (560 mmHg, 75 kPa or more)
• Intake air temp. : –8°C, 18°F or higher
• Engine coolant temp. : 110°C, 230°F or lower
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