QuestionCar all of sudden died @ stoplight, since then has a rough start and rough idle (but generally does not die). Runs fine once it gets going. We replaced the fuel filter, no help. Any ideas where to start without just replacing things?
Thank you.
AnswerSymptom List:
P-0171 1/1 FUEL SYSTEM LEAN
P-0172 1/1 FUEL SYSTEM RICH
Test Note: All symptoms listed above are diagnosed using the same tests.
The title for the tests will be P-0171 1/1 FUEL SYSTEM LEAN.
When Monitored and Set Condition:
P-0171 1/1 FUEL SYSTEM LEAN
When Monitored: With the engine running in closed loop mode and the ambient/battery
temperature above 20 deg F and altitude < 8000 ft.
Set Condition: PCM conducts test to determine if fuel system is running too lean. If this
happens for 2 trips, MIL illuminates & a trouble code is stored. MIL remains on for more
than one trip but goes out if conditions that set code are not found on subsequent trips.
P-0172 1/1 FUEL SYSTEM RICH
When Monitored: With the engine running in closed loop mode and the ambient/battery
temperature above 20 deg F and altitude < 8000 ft.
Set Condition: PCM conducts a test to determine whether fuel system is running too rich.
If this happens for 2 trips, MIL illuminates & trouble code is stored. MIL remains on for
more than 1 trip but goes out if conditions that set code are not found on subsequent trips
POSSIBLE CAUSES
COOLANT SENSOR CALIBRATION FAILURE
ENGINE MECHANICAL PROBLEM
FUEL PRESSURE OUT OF SPECIFICATION
UPSTREAM O2 SENSOR HEATER DEFECT
FUEL SYSTEM RICH OR LEAN DOES NOT REOCCUR
