Intake Air Temperature (IAT) G42 , Checking

Intake Air Temperature (IAT) G42, Checking

NOTE: 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:

Diagnostic text Specified value
Intake Air Temperature (IAT) approx. ambient air temperature

If the specified value is not obtained:
- Continue the test according to the following table:

Indicated Cause Test
approx. -40 degrees C Open circuit or short
or approx. -46 degrees C circuit to (B+)
approx. 140 degrees C Short circuit to Ground (GND)

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 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 2 for resistance.

Use the chart below for the specified values:
- Area A: Resistance values 0 to 50 degrees C.
- Area A: Resistance values 0 to 50 degrees C.







Specified values:
Read-out examples:
- Range A, 30 degrees C equals a resistance of 1.5 to 2.0 k Ohms
- Range B, 80 degrees C equals a resistance of 275 to 375 Ohms

If any of the specified values are not obtained:
- Replace the Intake Air Temperature (IAT) Sensor G42.

Testing if display approx. -40 degrees C or approx. -46 degrees 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 degrees C:
- End diagnosis and switch ignition off.
- Replace the Intake Air Temperature (IAT) Sensor G42.

If indication remains at approx. -40 degrees C or -46 degrees C:

Testing if display approx. 140 degrees C:







- Disconnect the Intake Air Temperature (IAT) Sensor G42 electrical harness connector - arrow - .

If indication jumps to approx. -40 degrees C or -46 degrees C:
- End diagnosis and switch ignition off.
- Replace the Intake Air Temperature (IAT) Sensor G42.

If the indication remains at approx. 140 degrees 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.

If the manufacturers test box is not being used. Perform the following step.
- Remove the Motronic Engine Control Module (ECM) J220.







- 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.

Intake Air Temperature (IAT) Motronic Engine Control Module
G42 Sensor electrical harness (ECM) J220 electrical connector
connector terminals test box socket
1 85
2 108


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.

Final procedures
After the repair work, the following work steps must be performed in the following sequence:
1. Check the DTC memory. Diagnostic Mode 03 - Read DTC Memory
2. If necessary, erase the DTC memory. Diagnostic Mode 04 - Erase DTC Memory
3. If the DTC memory was erased, generate readiness code.

- End of diagnosis.