Intake Air Temperature Sensor, Checking

Special tools and workshop equipment required 

• Multimeter VAG 1526 or Multimeter VAG 1715
• Connector test kit VAG 1594
• Wiring diagram
• Chilling spray (commercially available)

Test requirements 

• Fuses in E-box (plenum chamber, left) must be OK: Refer to appropriate SYSTEMS WIRING DIAGRAM
  Fig 1: Identifying Fuses In E-Box (Plenum Chamber, Left)

  Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.
• 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.

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:

PID		Diagnostic text		Specified value:
15:		Intake Air Temperature (IAT)		approx. ambient temperature

If specified value is not obtained:

-- Continue test according to the following table:

Indicated (1)	Cause	Continue testing
approx. -40° C	Open circuit or short circuit to B+
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.

-- Remember the intake air temperature value.

-- Spray 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-.

-- 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 temperature jumps to approx. 140° C:

-- End diagnosis and switch ignition off.

-- Replace Mass Air Flow (MAF) Sensor -G70-.

-- 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 temperature jumps to approx. -40° C:

-- End diagnosis and switch ignition off.

-- Replace Mass Air Flow (MAF) Sensor -G70-.

-- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data.

-- Generate readiness code.

If temperature 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 Ω

-- Check wires for short circuit to each other, to vehicle Ground (GND) and to B+.

Specified value: ∞ Ω

-- 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 kΩ
• 80° C is in range B and corresponds to a resistance of 275 to 375 Ω

If specified value is not obtained:

-- Replace Mass Air Flow (MAF) Sensor -G70-.

-- 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-.

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 .
2. If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
3. If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .