Intake Air Temperature Sensor, Checking
Diagnostic Procedures
Intake Air Temperature Sensor, Checking
• When servicing terminals in the harness connector for the Intake Air Temperature (IAT) sensor, use only gold-plated terminals.
Special tools, testers and auxiliary items required
• Multimeter (VAG1526) or multimeter (VAG1715)
• Connector test kit (VAG1594)
• Wiring diagram
• Chilling spray (commercially available)
Test requirements
• Fuses in E-box (in plenum chamber, left) must be OK:
• Ground (GND) connections between engine and chassis 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 P position.
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:
* 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 duct for cylinder bank 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 diagnosis and switch ignition off.
If the intake air temperature does not drop:
- Replace Mass Air Flow (MAF) Sensor (G70).
• 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.
Continuation of test if indication is approx. -40° 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 indication jumps to approx. 140° C:
- End diagnosis and switch ignition off.
- Replace Mass Air Flow (MAF) Sensor (G70).
• 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.
If indication remains at approx. -40° C:
- End diagnosis and switch ignition off.
- Check wires according to wiring diagram.
Continuation of test if indication is approx. 140° C:
- Disconnect 5-pin connector from Mass Air Flow (MAF) Sensor (G70) with Intake Air Temperature (IAT) Sensor (G42) arrow.
If indication jumps to approx. -40° C:
- End diagnosis and switch ignition off.
- Replace Mass Air Flow (MAF) Sensor (G70).
• 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.
If indication remains at approx. 140° 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.
- 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: infinite ohms
- Erase DTC memory of Engine Control Module (ECM) , Diagnostic mode 4: Reset/erase diagnostic data.
- Generate 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° C, range B displays resistance values for the temperature range of 50 to 100° C.
Read-out examples:
• 30° C is in range A and corresponds to a resistance of 1.5 to 2.0 kohms
• 80° 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).
• 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.
If no malfunctions are detected in the wires and the resistance values are OK:
- Replace Motronic Engine Control Module (ECM) (J220).