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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 139 (ENGINE CONTROL SYSTEM - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P0141: HO2S 2 HEATER PERFORMANCE (BANK 1)CIRCUIT DESCRIPTION
1999 GMC Forward Control 5.7 R, Automatic

Circuit Description

1999 GMC Forward Control 5.7 R, AutomaticSECTION Circuit Description
WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares oxygen content of surrounding air with oxygen content of exhaust stream. When vehicle is first started, Powertrain Control Module (PCM) operates in an open loop mode, ignoring HO2S signal voltage when calculating air/fuel ratio. PCM supplies HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage range of 0-1000 mV that fluctuates greater than and less than bias voltage once in closed loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside HO2S minimize time required for sensors to reach operating temperature, and to provide an accurate voltage signal. HO2S 2 heater performance diagnostic will only run from a cold start and only once per key cycle. This DTC will set if HO2S 2 heater takes too long to heat based on HO2S 2 signal voltage input to PCM. HO2S 2 heater circuit is energized anytime the ignition key is in RUN position.

HO2S 2 has the following circuits:

  • High signal.
  • Low signal.
  • Heater ignition voltage.
  • Heater ground circuit.

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