Fuel System > Engine Control System > P0118 Engine Coolant Temperature Circuit High Input

Component Location

General Description

The Engine Coolant Temperature Sensor (ECTS) is located in the engine coolant passage of the cylinder head for detecting the engine coolant temperature. The ECTS uses a thermistor whose resistance changes with the temperature. The electrical resistance of the ECTS decreases as the temperature increases, and increases as the temperature decreases. The reference 5 V in the PCM is supplied to the ECTS via a resistor in the PCM. That is, the resistor in the PCM and the thermistor in the ECTS are connected in series. When the resistance value of the thermistor in the ECTS changes according to the engine coolant temperature, the output voltage also changes. During cold engine operation the PCM increases the fuel injection duration and controls the ignition timing using the information of engine coolant temperature to avoid engine stalling and improve drivability.

DTC Description

Checking output signals from ECTS every 80 sec. under detecting condition, if an output signal is above 4.9V for more than 40 sec., PCM sets P0118. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.

DTC Detecting Condition

Item

Detecting Condition

Possible cause

DTC Strategy

•	Open, Signal high

•	Poor connection

•	Open or short to battery in signal harness

•	Open in ground harness

•

ECTS

•

PCM

Enable
Conditions

Case 1

•	Time after start-up >120 sec.

Case 2

•	Time from IG "OFF" to IG "ON" > 360 min.

•	Intake air temperature ≥ -10°C(14°F)

•	Engine running

Threshold value

•	Engine coolant temperature sensor's voltage >4.9V

Diagnosis Time

•	Continuous (More than 40 sec. failure for every 80 sec. test)

MIL On Condition

•	2 Driving Cycle

Specification

Temp. (°C/°F)	Resistance (kΩ)	Temp. (°C/°F)	Resistance (kΩ)
-40(-40)	48.14	40(104)	1.15
-20(-4)	14.13 ~ 16.83	60(140)	0.59
0(32)	5.79	80(176)	0.32
20(68)	2.31 ~ 2.59

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 ECTS connector.

2.	IG "ON" and ENG "OFF"

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

Specification : Approx. 5V

Is the measured voltage within specification ?

	▶ Go to "Ground Circuit Inspection" procedure.
	▶ If voltage is 0V, go to "Check open in harness" as follows. If it 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 ECTS connector and PCM connector.

Measure resistance between signal and cluster terminals of ECTS 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 ECTS connector and PCM connector.

Measure resistance between signal terminal of ECTS harness connector and ECTS 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 ECTS connector and then IG "ON".

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

Measure voltage between signal and ground terminals of ECTS 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 open or contact resistance in harness, and go to "Verification of Vehicle Repair" procedure.

Component Inspection

■ Check ECTS Resistance

1.	IG "OFF" and disconnect ECTS connector.

Measure resistance between signal and ground terminals of ECTS connector as the temperature rises.

Specificaton :

Temp. (°C/°F)	Resistance (kΩ)
-40(-40)	48.14
-20(-4)	14.13 ~ 16.83
0(32)	5.79
20(68)	2.31 ~ 2.59
40(104)	1.15
60(140)	0.59
80(176)	0.32

Are 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.follows.
	▶Substitute with a known - good ECTS and check for proper operation. If the problem is corrected, replace ECTS 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.