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HOMESERVICE MANUALSCHEVROLET2001SUBURBAN C1500REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 49 (ENGINE CONTROLS - 8.1L - DESCRIPTION AND OPERATION)DESCRIPTION AND OPERATIONFUEL SYSTEM DESCRIPTIONRUN MODE
2001 Chevrolet Suburban C1500

Run Mode

2001 Chevrolet Suburban C1500SECTION Run Mode
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2001 GMC Yukon XL, 2001 GMC Sierra, 2001 GMC Cab & Chassis Sierra, 2001 GMC C3500 HD, and 2001 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The run mode has 2 conditions called Open Loop and Closed Loop. When the engine is first started and the engine speed is above a predetermined RPM, the system begins Open Loop operation. The PCM ignores the signal from the heated oxygen sensor (HO2S) and calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT), MAF, MAP, and TP sensors. The system stays in Open Loop until meeting the following conditions:

  • Both HO2S have varying voltage output, showing that they are hot enough to operate properly. This depends upon the engine temperature.
  • The ECT sensor is above a specified temperature.
  • A specific amount of time has elapsed after starting the engine.

Specific values for the above conditions exist for each different engine, and are stored in the electrically erasable programmable read-only memory (EEPROM). The system begins Closed Loop operation after reaching these values. In Closed Loop, the PCM calculates the air/fuel ratio, injector on-time, based upon the signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.

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