Hello and welcome to Just answer.com, Super mechanic here. Please DON’T hit accept until you are completely satisfied with the answer. About your vehicle.
That could be a number of things. There was a recall on some of them though. You may want to call the dealer and see if it is covered.
DATE: July, 2003
Mitsubishi Motors North America, Inc. (MMNA) is recalling certain 2003 Lancer Evolution vehicles for possible electrical corrosion in the rear oxygen sensor harness. This condition could cause the sensor to malfunction, set a diagnostic trouble code and illuminate the MIL. The Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) have been notified about this recall.
A sample copy of the customer notification letter is shown. (Customers in California may receive a slightly modified version.)
Water may enter the floorboard from body seam seal openings at the side sills and/or bulkhead. This water may cause electrical corrosion to occur in the heated rear oxygen sensor harness.
Inspect for water leakage at the side sills and bulkhead, and apply sealant if needed. Also inspect the heated rear oxygen sensor connector for signs of electrical corrosion. If necessary, install a subharness and replace the sensor.
DTC P0421: Warm Up Catalyst Efficiency Below Threshold TECHNICAL DESCRIPTION
DTC SET CONDITIONS Check Conditions
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
DIAGNOSIS Required Special Tool:
STEP 1. Check for exhaust leaks. Q: Are there any abnormalities? YES: Go to Step 2. NO: Repair it. Then go to Step 7.
Attachments are only available to registered users.
Q: Is the sensor operating properly? YES: Go to Step 3. NO: Refer to, DTC P0136 - Heated Oxygen Sensor Circuit (sensor 2), DTC P0137- Heated Oxygen Sensor Circuit Low Voltage (sensor 2), DTC P0138 - Heated Oxygen Sensor Circuit High Voltage (sensor 2), DTC P0139- Heated Oxygen Sensor Circuit Slow Response (sensor 2).
Q: Is the sensor operating properly? YES: Go to Step 4. NO: Refer to, DTC P0130 - Heated Oxygen Sensor Circuit (sensor 1), DTC P0131 - Heated Oxygen Sensor Low Voltage (sensor 1), DTC P0132 - Heated Oxygen Sensor Circuit High Voltage (sensor 1), DTC P0133 - Heated Oxygen Sensor Circuit Slow Response (sensor 1), DTC P0134 - Heated Oxygen Sensor Circuit No Activity Detected (sensor 1).
Q: Is the sensor operating properly? YES: Go to Step 5. NO: Replace the heated oxygen sensor (front). Then go to Step 7. STEP 5. Perform the OBD-II drive cycle.
Q: Is DTC P0421 set? YES: Replace the catalytic converter. Then go to Step 6. NO: The procedure is complete. STEP 6. Perform the OBD-II drive cycle.
Q: Is DTC P0421 set? YES: Replace the ECM or PCM. Then go to Step 7. NO: The procedure is complete. STEP 7. Perform the OBD-II drive cycle.
READINESS TEST STATUS PURPOSE The Readiness function also referred as I/M Readiness or I/M Flags indicate if a full diagnostic check has been "Completed" (is "Ready") for each non-continuous monitor. Enhanced I/M State Emission Programs will use the Readiness status (Codes) to see if the vehicle is ready for OBD-II testing. "Incomplete" (Not Ready) codes will be one of the triggers for I/M failure. OVERVIEW The engine control module (ECM) or power-train control module (PCM) monitors the following main diagnosis items and records whether the evaluation was completed or is incomplete. The Readiness codes were established for the I/M programs, thereby confirming that the vehicle was not tampered with by erasing the diagnostic trouble code(s) (DTC's) before I/M testing. The Readiness and DTC codes can be reset by disconnecting the battery or by erasing the codes with a scan tool. For this reason all Readiness codes must read "Complete" before I/M testing. When the monitors run and complete, the MUT-II will record the Readiness Code as "Complete" (General Scan Tools record as "Ready"). If the monitor did not run completely, the system then reads as "Incomplete" (General Scan Tools record as "Not Ready"). When the vehicle is operating normally and the OBD-II Drive Cycle is carried out, Readiness Code will set as "Complete" on the first drive cycle. If during the first drive cycle a fault is detected then, a second drive is required before the Readiness Code will "Complete." If the fault is still there, then a DTC will set.
I never had that type of problem with one, but wait, there may be someone who has. Let me open it back up. Thank you for your patience, no need to reply as that will lock the question back to me, someone should be along shortly, I'm sure.