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.
Circuit Description
PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made to fuel delivery is indicated by the long and short term fuel trim values. Ideal fuel trim value is about 128 (zero percent).
A fuel trim value greater than 128 indicates that PCM is adding fuel to compensate for a lean condition. A fuel trim value less than 128 indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC will set if PCM detects an excessively rich condition.
For duplication of DTC, ensure:
- DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0200, P0300, P0301, P0302, P0303, P0304, P0325, P0335, P0341, P0342, P0401, P0404, P0405, P0502, P0503, P0506, P0507, P0601, P0602, P1404, P1133 or P1441 are not set.
- IAT is -13 to 175°F (-25 to115°C).
- ECT is 140-239°F (60-115°C).
- MAP greater than 26 kPa.
- Vehicle speed is less than 72 MPH.
- Engine speed is 550-3400 RPM.
- Fuel trim index is less than 70 percent.
- EVAP purge is not occurring.
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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.