IAT Sensor, Checking
Diagnostic Procedures
IAT Sensor, Checking
• Use only gold-plated terminals when servicing terminals in the electrical harness connector of the MAF / IAT sensor (G70 / G42).
Special tools, testers and auxiliary items required
• Multimeter.
• Wiring diagram.
Test procedure
- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check
Start diagnosis
- Connect the scan tool.
- Engine MUST be at room temperature.
- Switch the ignition on.
- Using the scan tool, check the intake air temperature:
If the specified value was obtained:
- Fault may be intermittent. Check for proper connection, damaged wiring or loose terminals.
If the specified value was Not obtained:
Checking internal resistance
- Disconnect the IAT sensor ( G42) electrical harness connector.
- Using a multimeter, check the IAT sensor ( G42 ) terminals 1 to 2 for resistance.
Use the chart below for the specified values:
Specified values:
If the specified value was Not obtained:
- Replace the IAT sensor ( G42) Refer to the repair information.
If the specified values are obtained, continue the test according to the following table:
°°Testing if display approx. - 40 C to - 46 C:
- Disconnect the IAT sensor ( G42) electrical harness connector.
- Using a jumper wire, connect the 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:
- Switch ignition off.
- Replace the IAT sensor ( G42) Refer to the repair information.
If indication remains at approx. -40 °C or -46 °C:
Checking wiring
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) ( J623). Refer to the repair information.
- Disconnect the ECM harness.
- Using a multimeter, check the IAT sensor ( G42 ) electrical harness connector terminal 1 to the Motronic Engine Control Module (ECM) (J623) electrical harness connector T60 terminal 42 for an open circuit or a short to voltage, refer to the wiring diagram.
Specified values: Circuit continuity; 1.5 ohms max; Circuit voltage = 0 volts when disconnected from ECM (with ignition on).
If the specified value was Not obtained:
- Check the wiring for an open, high resistance or short circuit to Battery (+)
- Check the electrical harness connector for damage, corrosion, loose or broken terminals.
- If necessary, repair the faulty wiring connection.
If the specified value was obtained:
- Using a multimeter, check terminal 2 of the IAT sensor to engine ground.
Specified value: 1.5 ohms Max
If the specified value was Not obtained:
- Check the wiring for an open circuit or high resistance.
- 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 ground circuit:
- Replace the Motronic Engine Control Module (ECM) (J623). Refer to the repair information.
°Testing if display approx. 140 C:
- Disconnect the IAT sensor ( G42) electrical harness connector.
- Check the value indicated on the scan tool display.
If indication jumps to approx. -40° C or -46° C:
- Switch ignition off.
- Replace the IAT sensor ( G42) Refer to the repair information.
If the indication remains at approx. 140° C
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) ( J623). Refer to the repair information.
- Disconnect the ECM harness.
- Using a multimeter, check the IAT sensor ( G42 ) electrical harness connector terminal 1 to engine ground.
Specified value: OL or no continuity.
If the specified value was Not obtained:
- Check the wiring for a short circuit to Ground.
- If necessary, repair the faulty wiring connection.
- Check the electrical harness connector for damage, corrosion, loose or broken terminals.
If no malfunction is detected in the wiring and the sensor resistance was OK:
- Replace the Motronic Engine Control Module (ECM) (J623). Refer to the repair information.
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 ] Scan Tool Testing and Procedures.
2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Scan Tool Testing and Procedures.
3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Monitors, Trips, Drive Cycles and Readiness Codes.