Code No. P0112: Intake Air Temperature Sensor Circuit Low Input
OPERATION
- A power voltage of 5 V is applied to the intake air temperature sensor power terminal of air flow sensor from the engine-ECU connector terminal ATS.
- The power voltage is earthed to the engine-ECU connector terminal AFSE from the intake air temperature sensor.
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 Condition
- More than 2 seconds have passed since the engine starting sequence was completed.
Judgement Criterion
- Intake air temperature sensor output voltage is less than 0.2 V for 2 seconds, which means that actual intake air temperature is more than 115°C for 2 seconds.
FAIL-SAFE AND BACKUP FUNCTION
- Control as if the intake air temperature is 25°C.
PROBABLE CAUSES
- Failed intake air temperature sensor
- Short circuit or harness damage 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 5: 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 circuit to earth in ATS line between air flow sensor connector and engine-ECU 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 5: 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 (AFSE line).
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(1)Disconnect the connector, and measure at the wiring harness side.
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(2)Check the resistance between the air flow sensor connector (AFSE 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 harness damage in AFSE line between air flow sensor connector and engine-ECU 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 harness damage in ATS line between air flow sensor connector and engine-ECU 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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