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.
Diagnostic Aids
Normal scan voltage varies between .1 and 1.0 volt (100-999 mV) while in closed loop. Code 13 will set within one minute if voltage remains between .347 and .547 volt, but system will go into open loop in approximately 15 seconds after Code 13 is set.
Verify ground connections are clean and tight at terminals D6 and D7. An open circuit in these terminals will set a Code 13. If code is intermittent, see TESTS W/O CODES article in this section.
Check O2 sensor wire for induced voltage. Disconnect O2 sensor signal wire at sensor and ECM. Using DVOM, measure voltage on wire with engine running. If .3 volt (300 mV) or more is present, check signal wire shield and/or reroute signal wire away from any high voltage sources (ignition wires, battery cables, alternator "B" circuit, etc.).
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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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