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HOMESERVICE MANUALSISUZU1996TROOPER S, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 17 (ENGINE CONTROLS - TESTS W/CODES - 2.6L 4-CYL)CIRCUIT TESTINGDTC P0172 - FUEL TRIM SYSTEM RICHCIRCUIT DESCRIPTION
1996 Isuzu Trooper S, Automatic

Circuit Description

1996 Isuzu Trooper S, AutomaticSECTION Circuit Description
WARNING: This page is about a different car, the 1996 Honda Passport. However, it is still accessible from the selected car via links, so may be relevant.

PCM reads HO2S signal voltage and adjusts fuel delivery based on this voltage. A change made to fuel delivery is indicated by Long Term (LT) and Short Term (ST) FUEL TRIM values.

ST FUEL TRIM values change rapidly in response to HO2S signal voltages. These changes fine tune engine fueling. LT FUEL TRIM values change in response to trends in ST fuel trim. LT fuel trim makes coarse adjustments to fueling in order to re-center and restore control to ST fuel trim. LT and ST fuel trim can be read by using a scan tool.

Ideal FUEL TRIM value is about zero. Fuel trim value more than zero indicates that PCM is adding fuel to compensate for a lean condition. Fuel trim less than zero indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC will set if PCM detects an excessively rich or lean condition.

Conditions required to set DTC are:

  • No IAC DTCs set at idle.
  • No CKP, ECT, EGR, HO2S, IAT, MAF, MAP or TP sensor DTCs set.
  • No EVAP DTCs set.
  • No misfire or injector circuit DTCs set.
  • ECT 122-212°F (50-100°C).
  • IAT -40-248°F (-40-120°C).
  • BARO more than 72.5.
  • MAP is between 20-99 kPa.
  • TP ANGLE less than 95%.
  • Vehicle speed less than 85 MPH (136 km/h).
  • MAF 2-200 grams per second.
  • Fuel system is in closed loop.
  • Canister purge, if on, has a duty cycle greater than zero percent.
  • Engine speed 400-600 RPM.
  • Long term fuel trim about -23 percent.
  • Short term fuel trim about -11 percent.
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