Intake Air Temperature, Checking

Intake Air Temperature, Checking

• 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

• The Motronic Engine Control Module (ECM) ( J220 ) fuses 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.

• Ignition switched off.

Function test

- 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) Refer to Fuel Injection and Ignition Repair Information.

- 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 diagnosis and switch the ignition off.

If the intake air temperature does not decrease:

- Replace the Intake Air Temperature (IAT) Sensor (G42) Refer to Fuel Injection and Ignition Repair Information.

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 2 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) Refer to Fuel Injection and Ignition Repair Information.

°°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 diagnosis and switch ignition off.

- Replace the Intake Air Temperature (IAT) Sensor (G42) Refer to Fuel Injection and Ignition Repair Information.

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 diagnosis and switch ignition off.

- Replace the Intake Air Temperature (IAT) Sensor ( G42 ) Refer to Fuel Injection and Ignition Repair Information.

If the indication remains at approx. 140° C:

Checking wiring

Add as a work step to the procedure where required.

If the manufacturers test box is being used. Perform the following step.

- Install the test box. Refer to Fuel Injection and Ignition Repair Information.

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 terminals for an open circuit according to the wiring diagram.









Specified value: 1.5 ohms Max.

If the specification was not obtained:

- Check the wiring for a short circuit to each other, Battery (+), and Ground (GND).

- If necessary, repair the faulty wiring connection.

- Check the electrical harness connector for damage, corrosion, lose or broken terminals.

If no malfunction is detected in the wiring:

- Replace the Motronic Engine Control Module (ECM) (J220). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.

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.

- End of diagnosis.