Air Temperature Sensor ( Ambient / Intake ): Testing and Inspection
Intake Air Temperature Sensor 2, Checking
Special tools, testers and auxiliary items required
• Multimeter
• wiring diagrams
• Cool spray (commercially available).
• jumper wire
• Use only gold-plated terminals when servicing terminals in harness connector of Intake Air Temperature (IAT) Sensor (G299 ).
Test requirements
• Fuses of Motronic Engine Control Module (ECM) ( J623 ) OK.
• Battery voltage at least 12.5 volts.
• 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 customers complaint. Refer to => [ Preliminary Check ] Preliminary Check
• Start diagnosis
Function test
- Connect the scan tool.
- Switch ignition on.
- Select "Diagnostic mode 1: Check measured values".
- Select 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 specified value is obtained:
- Remove Intake Air Temperature (IAT) Sensor (G299 ).
- Spray Intake Air Temperature (IAT) Sensor ( G299 ) with commercially available chilling spray while observing temperature value.
The temperature value must decrease.
- End diagnosis and switch ignition off.
If intake air temperature does not sink:
- Replace Intake Air Temperature (IAT) Sensor ( G299 ).
°°Testing if display approx. -40 C or approx. -46 C:
- Disconnect the electrical harness connector - 1 - from Intake Air Temperature (IAT) Sensor (G299 ).
- Check the electrical harness connector for damage, corrosion, loose or broken terminals.
- Using a jumper wire, connect electrical harness connector terminals 1 + 2 together and observe the indication on display.
If indication jumps to approx. 140° C:
- End diagnosis and switch ignition off.
- Replace Intake Air Temperature (IAT) Sensor ( G299 ).
If indication remains at approx. -40° C or -46° C:
- Check the wiring for a short circuit to Battery positive (+) or an open circuit.
- If necessary, repair the wiring connection.
- End diagnosis and switch ignition off.
°Testing if display approx. 140 C:
- Disconnect the electrical harness connector - 1 - from Intake Air Temperature (IAT) Sensor (G299 ).
If indication jumps to approx. -40° C or -46° C:
- End diagnosis and switch ignition off.
- Replace Intake Air Temperature (IAT) Sensor ( G299 ).
If indication remains at approx. 140° C:
- Check the wiring for a short circuit to Battery positive (+) or an open circuit.
- If necessary, repair the wiring connection.
- End diagnosis and switch ignition off.
Checking wiring
- Using a Multimeter, check the following wiring connection for an open circuit.
Specified resistance 1.5 ohms 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 the wiring:
- Using multimeter , check Intake Air Temperature (IAT) Sensor (G299 ) component terminals 1+2 for resistance.
• Area A: Resistance values for temperature range 0 to 50° C.
• Area B: Resistance values for temperature range 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 375ohms
If the specification is not obtained:
- Replace Intake Air Temperature (IAT) Sensor ( G299 ).
If the specification is obtained:
- Erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.
- Perform a road test to verify repair.
If the DTC does not return:
Repair complete, Generate readiness code. Refer to => [ Readiness Code ] Readiness Code.
- End diagnosis.
If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:
- Replace the Engine Control Module (ECM) (J623 ) => [ Motronic Engine Control Module, Replacing ] Motronic Engine Control Module, Replacing.
- Assembly is performed in the reverse of the removal.
Final procedures
After the repair work, the following work steps must be performed in the following sequence:
1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Mode 03 - Read DTC Memory.
2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.
3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code, Setting ] Readiness Code, Setting.
End of Diagnosis.