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.
SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSMITSUBISHI2005LANCER EVOLUTION L4-2.0L DOHC TURBOREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTESTING AND INSPECTIONSYMPTOM RELATED DIAGNOSTIC PROCEDURESINSPECTION PROCEDURE 27
2005 Mitsubishi Lancer Evolution L4-2.0L DOHC Turbo
Inspection Procedure 27
2005 Mitsubishi Lancer Evolution L4-2.0L DOHC TurboSECTION Inspection Procedure 27
Incorrect Idle Speed When The A/C is Operating (A/C load Signal)
CIRCUIT OPERATION
- The ECM increases the engine idle speed by driving the IAC motor when the automatic compressor-ECU sends a "A/C on" signal to the module.
- The A/C-ECU detects how the air conditioning is applying load to the engine and converts the information to a voltage signal (High voltage = low load Low voltage = high load). This voltage signal is called "A/C switch 2 signal". The ECM receives this A/C switch 2 signal from the automatic compressor controller through terminal No.24 and determines the idle-up speed according to the high or low air conditioning load.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Malfunction of the A/C control system.
- Open or shorted circuit or improper connector contact.
- ECM failed.
DIAGNOSIS
STEP 1. Check connector C-121 at ECM for damage.
Q: Is the connector in good condition?
YES: Go to Step 2.
NO: Repair or replace it. Refer to Harness Connector Inspection. Then confirm that the malfunction symptom is eliminated.
STEP 2. Measure the output voltage at ECM harness side connector C-121.
1. Disconnect the connector C-121 and measure at the harness side.
2. Start the engine and run at idle.
3. Turn the A/C switch "ON".
4. Measure the voltage between terminal No.24 and ground.
- If atmospheric air temperature is 15 °C (59 °F) or less the voltage should measure 1 volt or less.
- If atmospheric air temperature is 18 °C (65.4 °F) more the voltage should measure battery positive voltage.
5. Turn the A/C switch "OFF".
6. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the measured voltage within the specified range?
YES: Replace the ECM. Then confirm that the malfunction symptom is eliminated.
NO: Refer to Heater Air Conditioning And Ventilation - Manual A/C Diagnosis - Symptom Chart.
A/C Switch 2 Signal Circuit:
CIRCUIT OPERATION
- The ECM increases the engine idle speed by driving the IAC motor when the automatic compressor-ECU sends a "A/C on" signal to the module.
- The A/C-ECU detects how the air conditioning is applying load to the engine and converts the information to a voltage signal (High voltage = low load Low voltage = high load). This voltage signal is called "A/C switch 2 signal". The ECM receives this A/C switch 2 signal from the automatic compressor controller through terminal No.24 and determines the idle-up speed according to the high or low air conditioning load.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Malfunction of the A/C control system.
- Open or shorted circuit or improper connector contact.
- ECM failed.
DIAGNOSIS
STEP 1. Check connector C-121 at ECM for damage.
Q: Is the connector in good condition?
YES: Go to Step 2.
NO: Repair or replace it. Refer to Harness Connector Inspection. Then confirm that the malfunction symptom is eliminated.
STEP 2. Measure the output voltage at ECM harness side connector C-121.
1. Disconnect the connector C-121 and measure at the harness side.
2. Start the engine and run at idle.
3. Turn the A/C switch "ON".
4. Measure the voltage between terminal No.24 and ground.
- If atmospheric air temperature is 15 °C (59 °F) or less the voltage should measure 1 volt or less.
- If atmospheric air temperature is 18 °C (65.4 °F) more the voltage should measure battery positive voltage.
5. Turn the A/C switch "OFF".
6. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the measured voltage within the specified range?
YES: Replace the ECM. Then confirm that the malfunction symptom is eliminated.
NO: Refer to Heater Air Conditioning And Ventilation - Manual A/C Diagnosis - Symptom Chart.
RENDER: 1.0x
NO RELATED
Recommended Tools & Savings
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
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.