With Generic Scan Tool
Intake Air Temperature (IAT) Sensor, Checking
NOTE: The Intake Air Temperature (IAT) sensor -G42- is a component of the Mass Air Flow (MAF) sensor -G70- and cannot be replaced individually.
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.
- 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: 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 given table.
Indicated 1) Cause
approx. -40°C Open circuit or short circuit to B+
or
approx. -46°C
approx. 140°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 2.
- Remember the intake air temperature value.
- Spray the sensor (arrow) with commercially available chilling spray and watch the temperature value. The temperature should decrease.
- End diagnosis and switch ignition off.
If the intake air temperature does not drop:
- Replace Mass Air Flow (MAF) Sensor -G70-, item 3.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. 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 or -46°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-, item 3.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
If indication remains at approx. -40 or -46°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 or -46°C:
- End diagnosis and switch ignition off.
- Replace Mass Air Flow (MAF) Sensor -G70-, item no. 3.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
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. Test Box, Connecting For Wiring Test
Vehicles with engine code AEG
- Check wires between test box and 5-pin connector for open circuit according to wiring diagram.
Terminal 1 + socket 40
Terminal 3 + socket 12
Wire resistance: max: 1.5 Ohms
Vehicles with engine code AVH, AZG
- 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
Continuation for all vehicles
- Also check wires for short circuit to each other, to vehicle Ground (GND) and to B+. Specified value: Infinite Ohms
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 ... 0.50°C, range B displays resistance values for the temperature range of 50 ... 0.100°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-, item 3.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. 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-.