Fuel System > Engine Control System > P1111 Intake Air Temperature Sensor Circuit Intermittent high

Component Location

General Description

The Intake Air Temperature Sensor (IATS) is installed into the Mass Air Flow Sensor (MAFS). The IATS uses a thermistor whose resistance changes with the temperature. The electrical resistance of the IATS decreases as the temperature increases, and increases as the temperature decreases. The 5 V power source in the PCM is supplied to the IATS via a resistor in the PCM. That is, the resistor in the PCM and the thermistor in the IATS are connected in series. When the resistance value of the thermistor in IATS changes according to the intake air temperature, the signal voltage also changes. Using this signal, the information of the intake air temperature, the PCM corrects basic fuel injection duration and ignition timing.

DTC Description

Checking output signals of IATS under detecting condition, if an ouput signal is intermittently over 4.9V, PCM sets P1111.

DTC Detecting Condition

Item

Detecting Condition

Possible Cause

DTC Strategy

•	Monitor the signal of IAT sensor

•	Poor Connection

•	Open or short in signal circuit

•	Open in ground circuit

•	Faulty IATS

•	Faulty PCM

Enable
Conditions

•	Engine running

•	No Vehicle speed sensor fault

•	No ECTS fault

•	No MAFS fault

•	Intake airflow < 15 g/s

•	Vehicle speed < 25kph(9.3mph)

•	Engine coolant temperature > 50°C(122°F)

Threshold value

•	Intermittently Intake air temperature sensor's voltage > 4.9V

Diagnosis Time

•	Continuous

MIL On Condition

•	DTC only (NO MIL ON)

Specification

Temp. (°C/°F)	Resistance (kΩ)	Temp. (°C/°F)	Resistance (kΩ)
-40(-40)	95.95 ~ 105.78	20(68)	3.42 ~ 3.61
-20(-4)	27.4 ~ 29.77	40(104)	1.43 ~ 1.5
0(32)	9.08 ~ 9.72	60(140)	0.66 ~ 0.69
10(50)	5.49 ~ 5.83	80(176)	0.33 ~ 0.34

Schematic Diagram

Signal Waveform And Data

The output signals of IATS & ECTS change smoothly without any rapid changes. Those have almost same characteristic signal during the early period after start. It means that the temperatures of intake air and engine coolant are depended on the temperature of atmosphere. Meanwhile, during the warming up, the output signal of ECTS is going up increasingly. but, the output signal of IATS changes a little bit. even it may not change almost. It means that the heat of engine does not affect on the temperature of intake air.

Monitor DTC Status

Check DTC Status

(1)	Connect scantool to Data Link Connector(DLC).

(2)

IG "ON".

(3)	Select "DTC" button, and then Press "DTC Status" to check DTC's information from the DTCs menu.

(4)	Read "DTC Status" parameter.

(5)

Is parameter displayed "Present fault"?

	▶ Go to "Terminal and connector inspection" procedure.
	▶ Fault is intermittent caused by poor contact in the sensor's and/or PCM's connector or was repaired and PCM memory was not cleared. Thoroughly check connectors for looseness, poor connection, ending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure.

Terminal And Connector Inspection

1.	Many malfunctions in the electrical system are caused by poor harness and terminal condition. Faults can also be caused by interference from other electrical systems, and mechanical or chemical damage.

2.	Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage.

Has a problem been found?

	▶ Repair as necessary and go to "Verification of Vehicle Repair" procedure
	▶ Go to "Signal Circuit Inspection" procedure.

Signal Circuit Inspection

■ Check voltage

1.	IG "OFF" and disconnect IATS connector.

2.	IG "ON" and ENG "OFF"

Measure voltage between signal terminal of IATS harness connector and chassis ground.

Specification : Approx. 5V

Is the measured voltage within specification ?

	▶ Go to "Ground Circuit Inspection" procedure.
	▶ If the voltage is 0V, go to "Check open in harness" as follows. If the voltage is more than 5.1V, go to "Check short to battery in harness" as follows.

■ Check short to battery in harness

1.	IG "OFF" and disconnect IATS connector and PCM connector.

2.	Measure resistance between signal terminal of IATS harness connector and power terminal of MAFS harness connector.

Measure resistance between signal terminal of IATS harness connector and signal terminal of MAFS harness connector.

Specification : Infinite

Is the measured resistance within specification?

	▶ Go to "Component Inspection" procedure.
	▶ Repair short to battery in harness and go to "Verification of Vehicle Repair" procedure.

■ Check open in harness

1.	IG "OFF" and disconnect IATS connector and PCM connctor.

Measure resistance between signal terminal of IATS harness connector and IATS signal terminal of PCM harness connector.

Specification : below 1Ω

Is the measured resistance within specification?

	▶ Go to "Ground Circuit Inspection" procedure.
	▶ Repair open in harness and go to "Verification of Vehicle Repair" procedure.

Ground Circuit Inspection

■ Check open in harness

1.	IG "OFF" and disconnect IATS connector and then IG "ON".

2.	Measure voltage between signal terminal of IATS harness connector and chassis ground.(Measurement "A")

Measure voltage between signal and ground terminals of IATS harness connector.(Measurement "B")

Specification : Voltage difference between measurement "A" and "B" is below 200mV.

Is the measured voltage within specification ?

	▶ Go to "Component Inspection" procedure.
	▶ Repair contact resistance or open in harness and go to "Verification of Vehicle Repair" procedure.

Component Inspection

■ Check resistance of IATS

1.	IG "OFF" and disconnect IATS connector.

Measure resistance between signal and ground terminals of IATS connector after checking out the temperature of IATS with scantool.

Specificaton :

Temp. (°C/°F)	Resistance (kΩ)
-40(-40)	95.95 ~ 105.78
-20(-4)	27.4 ~ 29.77
0(32)	9.08 ~ 9.72
10(50)	5.49 ~ 5.83
20(68)	3.42 ~ 3.61
40(104)	1.43 ~ 1.5
60(140)	0.66 ~ 0.69
80(176)	0.33 ~ 0.34

Is the measured resistance within specification ?

	▶ Substitute with a known - good PCM and check for proper operation. If the problem is corrected, replace PCM and go to "Verification of Vehicle Repair" procedure.
	▶ Substitute with a known - good IATS and check for proper operation. If the problem is corrected, replace IATS and go to "Verification of Vehicle Repair" procedure.

Verification Of Vehicle Repair

After a repair, it is essential to verify that the fault has been corrected.

1.	Connect scantool and select "DTC" button.

2.	Press "DTC Status" button and confirm that "DTC Readiness Flag" indicates "Completed". If not, drive the vehicle within conditions noted in the freeze frame data or enable conditions

3.	Read "DTC Status" parameter

Is parameter displayed "History(Not Present) fault"?

	▶ System performing to specification at this time. Clear the DTC
	▶ Go to the applicable troubleshooting procedure.