(f)
Read control system DTC code again to confirm that the
system has no DTC code.
No
Intermittent Fault. Refer to
Yes
Step 17
Diagnostic completed.
5. Repair Instructions:
Replace post-catalytic oxygen sensor. Refer to
Post-Catalytic Oxygen Sensor Replacement
2.2.7.23 DTC P0170 P0171 P0172 P2177 P2178 P2187 P2188
1. DTC Descriptor:
DTC
P0170
Close-Loop Control Down Stream Air-Fuel Ratio Self Learn Unreasonable
DTC
P0171
Close-Loop Control Down Stream Air-Fuel Ratio Self Learn Too Lean
DTC
P0172
Close-Loop Control Down Stream Air-Fuel Ratio Self Learn Too Rich
DTC
P2177
Close-Loop Control Down Stream Air-Fuel Ratio Self Learn Value Higher Than Maximum
DTC
P2178
Close-Loop Control Down Stream Air-Fuel Ratio Self Learn Value Lower Than Minimum
DTC
P2187
Close-Loop Control Down Stream Air-Fuel Ratio Self Learn Value Higher Than Maximum
(Low-Load Zone)
DTC
P2188
Close-Loop Control Down Stream Air-Fuel Ratio Self Learn Value Lower Than Minimum
(Low-Load Zone)
Engine Control Module (ECM) controls the close-loop Air-Fuel ratio Measure system that achieves optimal combination of
performance, fuel economy and emissions control. In the close-loop mode, the engine control module monitors heated oxygen
sensor (HO
2
S) signal voltage and adjusts fuel supply according to the signal. Changes in fuel supply will change the value of long-
term and short-term fuel supply adjustment. Short-term fuel supply adjustment will respond to heated oxygen sensor signal voltage
and rapidly change. These changes will fine tune the fuel supply. Long-term fuel supply adjustment will respond to the trend in short-
term fuel supply adjustment. Long-term fuel adjustment adjusts the fuel supply in order to return to the center of the short-term fuel
adjustment value and controls the short-term fuel adjustment. The ideal fuel adjustment value is around 0%. A positive value indicates
that engine control module is increasing fuel supply to compensate the lean Air-Fuel mixture. A negative value indicates that engine
control module is decreasing fuel supply to compensate the rich Air-Fuel mixture.
Engine
Control System JL4G18-D
2-123
EC718/EC718RV EC715/EC715RV 10/2009
Summary of Contents for EC715 2009
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