Air Temperature Sensor ( Ambient / Intake ): Testing and Inspection
Intake Air Temperature Sensor, Checking
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• The Intake Air Temperature (IAT) Sensor (G42) is part of the Mass Air Flow (MAF) Sensor (G70) and cannot be replaced separately.
• Use only gold-plated terminals when servicing terminals in the electrical harness connector of the Intake Air Temperature (IAT) Sensor (G42).
Special tools, testers and auxiliary items required
• Multimeter.
• Wiring diagram.
• Cool spray (commercially available).
Test requirements
• Fuse (SB44) OK.
• The Fuel Pump (FP) Relay (J17) OK.
• Battery voltage at least 12.5 volts.
• All electrical consumers such as, lights and rear window defroster, switched off.
• Vehicles with automatic transmission, shift selector lever into position "P" or "N".
• A/C switched off.
• Ground (GND) connections between engine/transmission/chassis OK.
• Coolant Temperature at least 80° C.
• Ignition switched off.
Test procedure
- Perform a preliminary check to verify the customers complaint. Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.
Start diagnosis
- Connect the scan tool.
- Switch the ignition on.
- Using the scan tool, check the intake air temperature:
If the specified value is not obtained:
- Continue the test according to the following table:
If the specified values are obtained:
- Remove the Intake Air Temperature (IAT) Sensor (G42)
- Spray the Intake Air Temperature (IAT) Sensor (G42) with a commercially available cool spray while observing the temperature value on the scan tool.
The temperature value must decrease.
- End of diagnosis and switch the ignition off.
If the intake air temperature does not decrease:
- Replace the Intake Air Temperature (IAT) Sensor (G42)
If the intake air temperature does decrease:
Checking internal resistance
- Disconnect the Intake Air Temperature (IAT) Sensor (G42) electrical harness connector - arrow -.
- Using a multimeter, check the Intake Air Temperature (IAT) Sensor (G42) terminals 1 to 3 for resistance.
Use the chart below for the specified values:
• Area A: Resistance values 0 to 50° C.
• Area B: Resistance values 50 to 100° C.
Specified values:
Read-out examples:
• Range A, 30° C equals a resistance of 1.5 to 2.0 kohms
• Range B, 80° C equals a resistance of 275 to 375ohms
If any of the specified values are not obtained:
- Replace the Intake Air Temperature (IAT) Sensor (G42).
°°Testing if display approx. -40 C or approx. -46 C:
- Disconnect the Intake Air Temperature (IAT) Sensor (G42) electrical harness connector - arrow -.
- Using a jumper wire, connect the Intake Air Temperature (IAT) Sensor (G42) electrical harness connector terminals 1 to 2.
- Check the value indicated on the scan tool display.
If indication jumps to approx. 140° C:
- End of diagnosis and switch ignition off.
- Replace the Intake Air Temperature (IAT) Sensor (G42)
If indication remains at approx. -40 °C or -46 °C:
°Testing if display approx. 140 C:
- Disconnect the Intake Air Temperature (IAT) Sensor (G42) electrical harness connector - arrow -.
If indication jumps to approx. -40 °C or -46 °C:
- End of diagnosis and switch ignition off.
- Replace the Intake Air Temperature (IAT) Sensor (G42)
If the indication remains at approx. 140 °C:
Checking wiring
If the manufacturers test box is being used. Perform the following step.
- Install the Adapter Cable (121 Pin) (VAG1598/31)
If the manufacturers test box is not being used. Perform the following step.
- Remove the Motronic Engine Control Module (ECM) (J220). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.
- Using a Multimeter, check the Intake Air Temperature (IAT) Sensor (G42) electrical harness connector terminals to the Motronic Engine Control Module (ECM) (J220) electrical harness connector T121 terminals for resistance.
Specified value: 1.5 ohms Max.
If the specification was not obtained:
- Check the wiring for an open circuit, short circuit to each other, Battery (+), and Ground (GND).
- Check the electrical harness connector for damage, corrosion, loose or broken terminals.
- If necessary, repair the faulty wiring connection.
If no malfunction is detected in the wiring:
- Erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.
- Perform a road test to verify repair.
If the DTC does not return:
Repair complete, Generate readiness code. Refer to => [ Readiness Code ] Readiness Code.
- End of diagnosis.
If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:
- Replace the Motronic Engine Control Module (ECM) (J220). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.
- Assembly is performed in the reverse of the removal.
Final procedures
After the repair work, the following work steps must be performed in the following sequence:
1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Mode 03 - Read DTC Memory.
2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.
3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Readiness Code.