Intake Air Temperature (IAT) Sensor, Checking
Intake Air Temperature (IAT) Sensor, Checking
NOTE: When servicing terminals in the harness connector for the Intake Air Temperature (IAT) sensor, use only gold-plated terminals.
Recommended special tools and equipment
- V.A.G 1526 multimeter or V.A.G 1715 multimeter
- V.A.G 1594 connector test kit
- Wiring diagram
- Chilling spray (commercially available)
Test requirements
- Fuses in E-box (plenum chamber, left) must be OK
- Ground (GND) connections between engine and chassis must be
- Parking brake must be engaged or else daylight driving lights will be switched on.
- For vehicles with automatic transmission, selector lever must be in -P-.
Function test
- Connect diagnostic tester.
- Switch ignition on.
- Under address word 33, select "Diagnostic mode 1: Checking measured values."
- Select the measuring value "PID 15: Intake air temperature".
- Check specified value of intake air temperature:
If specified value is not obtained:
- Continue test according to the following table:
Indicated1) Cause
approx. -40 degrees C Open circuit or short circuit to B+
approx. 140 degrees C Short circuit to Ground (GND)
1) If a temperature is indicated which is below the ambient temperature of sensor, first check sensor wires for contact resistance. Note that while the vehicle is standing still the sensor might warm up due to radiant heat.
If specified value is obtained:
- Remove intake air hose between Mass Air Flow (MAF) sensor and throttle valve control module.
- Remember the intake air temperature value.
- Spray sensor (arrow) with commercially available chilling spray and watch the temperature value. The temperature must decrease.
- End diagnosis and switch ignition off.
If the intake air temperature does not drop:
- Replace Mass Air Flow (MAF) Sensor -G70-.
NOTE: The Intake Air Temperature (IAT) sensor -G42- is a component of the Mass Air Flow (MAF) sensor -G70- and cannot be replaced individually.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code
Continuation of test if indication is approx. -40 degrees C:
- Disconnect 5-pin connector from Mass Air Flow (MAF) Sensor -G70- with Intake Air Temperature (IAT) Sensor -G42- (arrow).
- Bridge terminals 1 + 3 of connector using the respective adapter cables while observing the indication on display.
If temperature jumps to approx. 140 degrees C:
- End diagnosis and switch ignition off.
- Replace Mass Air Flow (MAF) Sensor -G70-.
NOTE: The Intake Air Temperature (IAT) sensor -G42- is a component of the Mass Air Flow (MAF) sensor -G70- and cannot be replaced individually.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code
If indication remains at approx. -40 degrees C:
- End diagnosis and switch ignition off.
- Check wires according to wiring diagram.
Continuation of test if indication is approx. 140 degrees C:
- Disconnect 5-pin connector from Mass Air Flow (MAF) Sensor -G70- with Intake Air Temperature (IAT) Sensor -G42- (arrow).
If temperature jumps to approx. -40 degrees C:
- End diagnosis and switch ignition off.
- Replace Mass Air Flow (MAF) Sensor -G70-.
NOTE: The Intake Air Temperature (IAT) sensor -G42- is a component of the Mass Air Flow (MAF) sensor -G70- and cannot be replaced individually.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code
If temperature remains at approx. 140 degrees C:
- End diagnosis and switch ignition off.
- Check wires according to wiring diagram.
Checking wiring
- Connect test box to control module wiring harness, connect test box for wiring test. Test Box, Connecting For Wiring Test
- Check wires between test box and 5-pin connector for open circuit according to wiring diagram.
Terminal 1 + socket 26
Terminal 3 + socket 27
Wire resistance: max. 1.5 ohms
- Check wires for short circuit to each other, to vehicle Ground (GND) and to B+.
Specified value: infinity ohm
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code
If no malfunctions are found in wire:
- Measure resistance at Intake Air Temperature (IAT) sensor -G42-, terminals 1 (signal) and 3 (Ground -GND-).
Range A displays resistance values for the temperature range of 0 to 50 degrees C, range B displays resistance values for the temperature range of 50 to 100 degrees C.
Read-out examples:
- 30 degrees C is in range A and corresponds to a resistance of 1.5 to 2.0 kohms
- 80 degrees C is in range B and corresponds to a resistance of 275 to 375 ohms
If specified value is not obtained:
- Replace Mass Air Flow (MAF) Sensor -G70-.
NOTE: The Intake Air Temperature (IAT) sensor -G42- is a component of the Mass Air Flow (MAF) sensor -G70- and cannot be replaced individually.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code
If no malfunctions are detected in the wires and the resistance values are OK:
- Replace Motronic Engine Control Module (ECM) -J220-.