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 MANUALSMITSUBISHI2004LANCER L4-2.0L SOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSSENSORS AND SWITCHES - COMPUTERS AND CONTROL SYSTEMSAIR FLOW METER/SENSORTESTING AND INSPECTION
2004 Mitsubishi Lancer L4-2.0L SOHC
Air Flow Meter/Sensor: Testing and Inspection
2004 Mitsubishi Lancer L4-2.0L SOHCSECTION Testing and Inspection
INSPECTION PROCEDURE USING AN OSCILLOSCOPE
VOLUME AIRFLOW SENSOR
Required Special Tool:
MB991709: Test Harness Set
Measurement Method
1. Disconnect the volume airflow sensor connector, and connect the test harness special tool (MB991709) in between. (All terminals should be connected.)
2. Connect the oscilloscope probe to volume airflow sensor connector terminal No. 3.
Alternate method (Test harness not available)
1. Connect the oscilloscope probe to ECM terminal No. 90.
1. Connect the oscilloscope probe to PCM terminal No. 65.
Standard wave pattern
Observation conditions
Rev engine, observe T1 and T2 remain equal.
Wave Pattern Observation Points
Check that cycle time T becomes shorter and the frequency increases when the engine speed is increased.
Examples of Abnormal Wave Patterns
Example 1
Cause of problem
- Sensor interface malfunction.
Wave pattern characteristics
- Rectangular wave pattern is output even when the engine is not started.
Example 2
Cause of problem
- Damaged rectifier or vortex generation column.
Wave pattern characteristics
- Unstable wave pattern with non-uniform frequency. An ignition leak will distort the wave pattern temporarily, even if the volume airflow sensor is normal.
VOLUME AIRFLOW SENSOR
Required Special Tool:
MB991709: Test Harness Set
Measurement Method
1. Disconnect the volume airflow sensor connector, and connect the test harness special tool (MB991709) in between. (All terminals should be connected.)
2. Connect the oscilloscope probe to volume airflow sensor connector terminal No. 3.
Alternate method (Test harness not available)
1. Connect the oscilloscope probe to ECM terminal No. 90.
1. Connect the oscilloscope probe to PCM terminal No. 65.
Standard wave pattern
Observation conditions
Rev engine, observe T1 and T2 remain equal.
Wave Pattern Observation Points
Check that cycle time T becomes shorter and the frequency increases when the engine speed is increased.
Examples of Abnormal Wave Patterns
Example 1
Cause of problem
- Sensor interface malfunction.
Wave pattern characteristics
- Rectangular wave pattern is output even when the engine is not started.
Example 2
Cause of problem
- Damaged rectifier or vortex generation column.
Wave pattern characteristics
- Unstable wave pattern with non-uniform frequency. An ignition leak will distort the wave pattern temporarily, even if the volume airflow sensor is normal.
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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.