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.
Code 26, O2 Sensor CKT, Rich Exhaust Indicated: Notes
Oxygen (O2) sensor produces a varying voltage as engine reaches normal operating temperature. Voltage will vary from .1 (lean) to 1.0 (rich) volt. PCM monitors voltage and determines concentration of gases in exhaust and adjusts fuel to maintain air/fuel ratio.
Code 26 will set if engine speed varies more than 15 RPM over preceding crank angle period for 30 seconds while idling with engine coolant temperature greater than 122°F (50°C).
- Checks for faulty O2 sensor.
- Checks for open in Black wire between PCM and O2 sensor.
- Checks for open in Brown wire between PCM and G106.
- Checks for short to ground in Black wire between PCM and O2 sensor, open in Brown wire to O2 sensor (Federal emissions only), and a faulty PCM.
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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.
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