Code No. P0072: Intake Air Temperature Sensor Circuit Low Input
OPERATION
- A power voltage of 5 V is applied to the Intake air temperature sensor output terminal from the engine-ECU connector terminal ATS.
- The power voltage is earthed to the engine-ECU connector terminal ATSE from the Intake air temperature sensor connector terminal.
FUNCTION
- The Intake air temperature sensor converts the intake air temperature into a voltage and inputs the voltage signal to the engine-ECU.
- In response to the signal, the engine-ECU corrects the fuel injection amount, etc.
- The Intake air temperature sensor is a kind of resistor, which has characteristics to reduce its resistance as the intake air temperature rises. Therefore, the sensor output voltage varies with the intake air temperature, and becomes lower as the intake air temperature rises.
TROUBLE JUDGEMENT
Check Conditions
- Battery positive voltage is 8 - 16 V
- 2 seconds later after the ignition switch has been in "ON" position or the engine has started up.
Judgement Criterion
- The Intake air temperature sensor output voltage is 0.05 V or less (the intake air temperature is above 150°C or equivalent).
FAIL-SAFE AND BACKUP FUNCTION
- The intake air temperature is controlled to be 50°C.
- The EGR control is stopped (fully closed).
- The DPF regeneration is prohibited.
PROBABLE CAUSES
- Failed Intake air temperature sensor
- Short circuit in Intake air temperature sensor circuit or loose connector contact
- Failed engine-ECU
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STEP 1. M.U.T.-III data list
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- Item 43: Intake air temperature sensor
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OK: At ambient temperature (atmospheric temperature) or equivalent.
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Q.
Is the check result normal?
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 Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions).
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 Go to Step 2.
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STEP 2. Check intake air temperature sensor itself.
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- Check Intake air temperature sensor itself (Refer to
 ).
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Q.
Is the check result normal?
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Go to Step 3.
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Replace the air flow sensor.
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STEP 3. Voltage measurement at air flow sensor connector (ATS line).
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(1)Disconnect the connector, and measure at the wiring harness side.
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(3)Check the voltage between the air flow sensor connector (ATS line) and body earth.
OK: 4.5 - 4.9 V
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Q.
Is the check result normal?
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Go to Step 6.
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Go to Step 4.
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STEP 4. Check of short to earth in ATS line between engine-ECU connector and air flow sensor connector.
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Q.
Is the check result normal?
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Go to Step 5.
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Repair the connector(s) or wiring harness.
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STEP 5. M.U.T.-III data list
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- Item 43: Intake air temperature sensor
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OK: At ambient temperature (atmospheric temperature) or equivalent.
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Q.
Is the check result normal?
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Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions).
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Replace the engine-ECU.
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STEP 6. Resistance measurement at air flow sensor connector (ATSE line).
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(1)Disconnect the connector, and measure at the wiring harness side.
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(2)Measure the resistance between the air flow sensor connector (ATSE line) and body earth.
OK: Continuity (2 Ω or less)
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Q.
Is the check result normal?
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Go to Step 8.
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Go to Step 7.
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STEP 7. Check of damage in ATSE line between engine-ECU connector and air flow sensor connector.
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Q.
Is the check result normal?
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Go to Step 5.
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Repair the connector(s) or wiring harness.
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STEP 8. Check of damage in ATS line between engine-ECU connector and air flow sensor connector.
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Q.
Is the check result normal?
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Go to Step 5.
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Repair the connector(s) or wiring harness.
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