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.
DTC P0139: Secondary Heated Oxygen Sensor (Secondary Ho2S) Slow Response (Sensor 2)
Perform PCM reset procedure. See PCM RESET PROCEDURE/CLEARING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM. Start engine. Hold engine speed at 3000 RPM with no load and transmission in Park or Neutral until radiator fan comes on. Using scan tool, check secondary HO2S (Sensor 2) output voltage with engine running at 3000 RPM. If voltage stays within 0.3-0.6 volt for 2 minutes, replace secondary HO2S (Sensor 2). If voltage does not stay within 0.3-0.6 volt for 2 minutes, problem is intermittent. System is okay at this time. Check for poor connections or loose wires at connectors C444 (located behind right kick panel), secondary HO2S (sensor 2) and PCM. See appropriate wiring diagram under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. Repair as necessary.
NO RELATED
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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.