Air Temperature Sensor ( Ambient / Intake ): Testing and Inspection

Checking Intake Air Temperature (IAT) sensor


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
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram
- Chilling spray (commercially available)

Test requirements







- The respective fuses of Motronic Engine Control Module (ECM) -J220- must be OK.







- Fuses -1, 2, 3, 4 and 7- in protective housing (plenum chamber, left) must be OK:
- Parking brake must be engaged or else daylight driving lights will be switched on.
- For vehicles with automatic transmission, selector lever must be in position -P-or -N-.

Function test
- Connect diagnostic tester. Diagnostic Tester, Connecting
- Switch ignition on.
- Under address word 33, select "Diagnostic mode 1: Check 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:

Indicated 1) 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, item 1.
- Remember the intake air temperature value.







- Spray the sensor (arrow) with commercially available chilling spray and watch the temperature value. The temperature must decrease.
- End diagnostic and switch ignition off.

If the intake air temperature does not drop:
- Replace Mass Air Flow (MAF) Sensor-G70-, item 15 .


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.
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

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- (-1-).







- Bridge terminals 1 + 3 of connector using the respective adapter cables while observing the indication on display.

If indication jumps to approx. 140 degrees C:
- End diagnostic and switch ignition off.
- Replace Mass Air Flow (MAF) Sensor -G70-, item 15 .


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.
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

If indication remains at approx. -40 degrees C:
- End diagnostic 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- (-1-).

If indication jumps to approx. -40 degrees C:
- End diagnostic and switch ignition off.
- Replace Mass Air Flow (MAF) Sensor -G70-, item 15 .


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.
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

If indication remains at approx. 140 degrees C:
- End diagnostic 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

- Also check wires for short circuit to each other, to vehicle Ground (GND) and to B+.
Specified value: Infinity Ohms
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

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...50 degrees C, range B displays resistance values for the temperature range of 50...100 degrees C

Read-out examples:
- 30 degrees C is in range A and corresponds to a resistance of 1.5 to 2.0 k Ohms
- 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-, item 15 .


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.
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

If no malfunctions are detected in the wires and the resistance values are OK:
- Replace Motronic Engine Control Module (ECM) -J220-.