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HOMESERVICE MANUALSCHEVROLET1999SUBURBAN C2500, 6.5 FREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P0135-P0204DTC P0172DTC P0172: FUEL TRIM SYSTEM RICH-BANK 1 (3.8L "F" BODY)CIRCUIT DESCRIPTION
1999 Chevrolet Suburban C2500, 6.5 F

Circuit Description

1999 Chevrolet Suburban C2500, 6.5 FSECTION Circuit Description

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 greater 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.

For duplication of DTC, ensure:

  • No misfire, HO2S, EVAP system, IAC, fuel injector circuit, ECT, EGR, IAT, MAF, MAP or TP sensor DTCs are set.
  • Engine speed is 500-4000 RPM.
  • ECT is 68-230°F (20-110°C).
  • IAT is 0-104°F (-18-40°C).
  • BARO is greater than 10.7 psi (0.75 kg/cm2 ).
  • MAP is 2.6-12.8 psi (0.18-0.90 kg/cm2 ).
  • TP angle is less than 90 percent.
  • MAF is 9-180 grams per second.
  • Long term fuel trim is near maximum authority (-23).
  • Short term fuel trim is near maximum authority (-11).
  • Vehicle speed is less than 70 MPH.
  • Conditions are met in FUEL TRIM CELLS 0, 1, 2, 6, and/or 7.

RENDER: 1.0x

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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

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  • • The engine overheats, stalls repeatedly, or misfires under load.
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