Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Intake Air Temperature / Manifold Absolute Pressure Sensor, Checking
The Intake Air Temperature (IAT) Sensor -G42- and the Manifold Absolute Pressure (MAP) Sensor -G71- are integrated into one unit and cannot be serviced separately.
Special tools and workshop equipment required
- Multimeter.
- Wiring diagram.
Test Requirements
- Engine Control Module (ECM) -J623- fuse OK.
- Battery voltage at least 12.5 V.
- All electrical consumers such as, lights and rear window defroster, switched off.
- Vehicles with automatic transmission, shift selector lever into position "P" or "N".
- A/C switched off.
- Ground (GND) connections between engine/transmission/chassis OK.
- Ignition switched off.
Test Procedure
-- Perform a preliminary check to verify the customer's complaint. Refer to PRELIMINARY CHECK .
Function test
-- Connect the scan tool.
-- Start the engine and let run at idle.
-- Using the scan tool, check the engine speed:
| Diagnostic text | Specified value | |||
|---|---|---|---|---|
| Intake air temperature | approx. ambient temperature. | |||
-- End diagnosis and switch ignition off.
If a temperature is indicated which differs greatly from ambient temperature of sensor, check sensor and sensor wires for contact resistances and open circuit.
-- End diagnosis and switch the ignition off.
If the specified value was not obtained:
Checking voltage supply
-- Disconnect the electrical harness connector -4- from the Intake Air Temperature (IAT) Sensor -G42-.
-- Using aMultimeter --, check the Intake Air Temperature (IAT) SensorG42electrical harness connector for voltage.
| Intake Air Temperature (IAT) SensorG42Harness Connector Terminal | Specified value |
|---|---|
| 1 to B+ | Battery positive (+) |
| 2 to Ground (GND) | 5V or less |
| 3 to Ground (GND) | about 5 V |
| 4 to Ground (GND) | Battery positive (+) |
If the specified value is obtained:
-- Replace the Intake Air Temperature (IAT) Sensor -G42-.
If specified value is not obtained:
Checking wiring connections
If the manufacturers test box is being used, perform the following step.
-- Connect the Test Box 105 Pin VAG1598/42 with Adapter Cable1598/39-1. Refer to Component Locations Overview .
If the manufacturers test box is not being used, perform the following step.
-- Using aMultimeter, check the following wire connection for an open circuit.
| Intake Air Temperature (IAT) SensorG42Harness Connector Terminal | Engine Control Module (ECM) -J623- Electrical Harness Connector Terminals |
|---|---|
| 1 | 40 |
| 2 | 39 |
| 3 | 29 |
| 4 | 44 |
Specified value: 1.5 Ω max.
If the specification is not obtained:
-- Check the wiring for a short circuit to Battery positive (+) or an open circuit.
-- If necessary, repair the wiring connection.
If no malfunctions are found in wires:
-- Replace the Engine Control Module (ECM) -J623-. Refer to ENGINE CONTROL MODULE, REPLACING .
-- Assembly is performed in the reverse of the removal.
After repair work, the following work steps must be performed in the following sequence:
- Check the DTC memory. Refer to DIAGNOSTIC MODE 03 - READ DTC MEMORY .
- If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
- If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.