Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 139 (ENGINE CONTROL SYSTEM - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P0140: HO2S 2 CIRCUIT INSUFFICIENT ACTIVITY (BANK 1)TEST DESCRIPTION
1999 GMC Forward Control 5.7 R, Automatic
Test Description
1999 GMC Forward Control 5.7 R, AutomaticSECTION Test 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.
The numbers below refer to the step numbers in the diagnostic procedures.
- 2 - HO2S 2 voltage may default to bias voltage. DTC should be cleared and freeze frame/failure records data recorded before proceeding. A normally functioning HO2S 2 voltage signal will fluctuate greater than and less than bias voltage amount. Action in test step should result in a visible reaction from HO2S 2 output.
- 4 - A voltage reading other than specified amount in this step indicates an open circuit condition in one of the signal circuits or PCM.
- 5 - This step inspects for an open circuit condition in signal circuits, independent of PCM.
- 7 - The conditions listed in the table may contribute to failure of HO2S. Conditions listed apply only to this type of failure.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.