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 MANUALSMITSUBISHI2001MIRAGE LS, 4D SEDAN, STANDARDREPAIR AND DIAGNOSISENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - SELF-DIAGNOSTICSDIAGNOSTIC TESTSDTC P0139: HO2S SLOW RESPONSE (SENSOR 2)DIAGNOSTIC PROCEDURE
2001 Mitsubishi Mirage LS, 4D Sedan, Standard
Diagnostic Procedure
2001 Mitsubishi Mirage LS, 4D Sedan, StandardSECTION Diagnostic Procedure
NOTE:
After repairs, verify repair by driving vehicle according to appropriate monitor drive cycle and check for DTCs. See VERIFYING REPAIRS
.
- Start engine. Using scan tool, check data list item No. 59 rear Heated Oxygen Sensor (HO2S). With engine warm and racing, when RPM is rapidly decreased to idle, rear HO2S output voltage should fall to 0.15 or less within three seconds. If scan tool readings are not as specified, go to next step. If scan tool readings are as specified, problem is intermittent. See INTERMITTENT DIAGNOSTIC TROUBLE CODES under ON-BOARD DIAGNOSTICS under SELF-DIAGNOSTIC SYSTEM.
- Replace rear HO2S. Go to next step
- Reinstall components, using scan tool, clear DTCs. Test drive vehicle according to appropriate OBD-II DRIVE CYCLES and check for DTCs. See HEATED OXYGEN SENSOR MONITOR under OBD-II DRIVE CYCLES under VERIFYING REPAIRS. Confirm DTC P0139 does not reset.
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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.