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.
1993 Mitsubishi Eclipse Base, AutomaticFACTORY OEM SERVICE PROCEDURE
Code 59: Rear Oxygen (O2) Sensor
NOTE:
For component terminal identification, see TERMINAL IDENTIFICATION
. For wiring diagrams, see WIRING DIAGRAMS
article in this section.
- If using scan tester, go to next step. Disconnect O2 sensor connector. Using DVOM, check continuity between O2 sensor terminals. 3 and 4. If continuity does not exist, replace O2 sensor. If continuity exists, go to step 3.
- With an assistant, road test vehicle. Drive vehicle with wide open throttle in 2nd gear (M/T) or "L" position (A/T). Using scan tester, read O2 sensor voltage. If O2 sensor voltage is not .6-1.0 volt at 3500 RPM, replace O2 sensor. If voltage is as specified, go to next step.
- Disconnect O2 sensor connector and MPI relay connector. Using DVOM, check for continuity between O2 sensor connector terminal No. 3 and MPI relay connector No. 2. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
- With O2 sensor connector disconnected, disconnect ECM connector. Check for continuity between O2 sensor connector terminal No. 1 and ECM connector terminal No. 55. If continuity does not exist, repair wiring harness as necessary. If continuity exists, go to next step.
- With O2 sensor connector disconnected, check for continuity between chassis ground and O2 sensor connector terminals No. 2and 4. If continuity does not exist on either circuit, repair wiring harness as necessary. If continuity exists and preceding test procedure did not discover any faults, replace O2 sensor.
Factory Service Tools
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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.