Mitsubishi Colt Ralliart. Manual - part 680

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI) <4G1>

13B-45

Code No. P0115: Engine Coolant Temperature Sensor System

OPERATION

• A power voltage of 5 V is applied to the engine 

coolant temperature sensor output terminal (ter-
minal No. 1) from the engine-ECU (terminal No. 
14).

• The engine coolant temperature sensor (terminal 

No. 2) is earthed to the engine-ECU (terminal No. 
29).

FUNCTION

• The engine coolant temperature sensor converts 

the engine coolant temperature into a voltage sig-
nal and inputs the signal to the engine-ECU. 

• In response to the signal, the engine-ECU con-

trols the fuel injection amount and fast idle speed 
when the engine is cold.

• The engine coolant temperature sensor is a kind 

of resistor, which has the property of decreasing 
in resistance with the increase of engine coolant 
temperature. Therefore, the sensor output volt-
age varies with the engine coolant temperature, 
lowering as the engine coolant temperature rises.

TROUBLE JUDGEMENT

Check Condition

• 2 seconds later from when ignition switch is in 

ON position

or

• 2 seconds later from when engine starts

AK402678

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52 53 54 555657585960616263646566

38 39 404142434445464748495051

22 23 24 252627282930313233343536

7

5

3

1

6

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2

29

14

A-114

Engine-ECU

Engine coolant
temperature sensor

Y-G

B

A-121

 (MU802406)

2

1

5 V

Engine Coolant Temperature Sensor Circuit

AF

Wire colour code
B: Black  LG: Light green  G: Green  L: Blue  W: White  Y: Yellow  SB: Sky blue  BR: Brown  O: Orange  GR: Gray
R: Red  P: Pink  V: Violet  P: Purple

Main

Index

Group

TOC

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI) <4G1>

13B-46

Judgement Criterion

• Sensor output voltage is more than 4.6 V for 4 

seconds. (Intake air temperature is less than 
-40

°C or equivalent.)

or

• Sensor output voltage is less than 0.1 V for 4 sec-

onds. (Intake air temperature is more than 120

°C 

or equivalent.)

Check Condition

• While engine is running

Judgement Criterion

• Engine coolant sensor output voltage rises to 

more than 1.6 V from less than 1.6 V. (Engine 
coolant temperature decreases to less than 40

°C 

or equivalent from more than 40

°C or equiva-

lent.)

• Then, for 5 minutes, engine coolant temperature 

output voltage is more than 1.6 V. (Engine cool-
ant temperature is less than 40

°C or equivalent.)

PROBABLE CAUSES

• Failed engine coolant temperature sensor

• Open/short circuit or damage in engine coolant 

temperature sensor circuit, or loose connector 
contact

• Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III data list

• Item 21: Engine coolant temperature sensor

OK:

When the engine is cold: Nearly equal to ambi-

ent temperature (atmospheric temperature)

When the engine is hot: 80 

− 120°C

Q: Is the check result normal?

YES : 

Intermittent malfunction (Refer to GROUP 

00 

− How to Use Troubleshooting/Inspection 

Service Points 

−How to Cope with 

Intermittent Malfunctions 

P.00-13

).

NO : 

Go to Step 2 .

STEP 2. Connector check: A-121 engine coolant 
temperature sensor connector

Q: Is the check result normal?

YES : 

Go to Step 3 .

NO : 

Repair or replace.

STEP 3. Perform resistance measurement at 
A-121 engine coolant temperature sensor 
connector.

• Disconnect connector and measure at sensor 

side.

• Resistance between terminals No. 1 and No. 2

OK:

Engine coolant temperature at 

−20°C: 14 − 17 

k

Ω

Engine coolant temperature at 0

°C: 5.1 − 6.5 kΩ

Engine coolant temperature at 20

°C: 2.1 − 2.7 

k

Ω

Engine coolant temperature at 40

°C: 0.9 − 1.3 

k

Ω

Engine coolant temperature at 60

°C: 0.48 − 

0.68 k

Ω

Engine coolant temperature at 80

°C: 0.26 − 

0.36 k

Ω

Q: Is the check result normal?

YES : 

Go to Step 4 .

NO : 

Replace engine coolant temperature 
sensor.

AK402085

1

2

AC

A-121(B)

Connector: A-121

Harness side 

connector

AK402085

1

2

AC

A-121(B)

Connector: A-121

Harness side 

connector

Main

Index

Group

TOC

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI) <4G1>

13B-47

STEP 4. Perform voltage measurement at A-121 
engine coolant temperature sensor connector.

• Disconnect connector and measure at harness 

side.

• Ignition switch: ON

• Voltage between terminal No. 1 and earth.

OK: 4.5 

− 4.9 V

Q: Is the check result normal?

YES : 

Go to Step 10 .

NO : 

Go to Step 5 .

STEP 5. Perform voltage measurement at A-114 
engine-ECU connector.

• Disconnect engine-ECU connector, and connect 

special tool power plant ECU check harness 
(MB991987) and measure the voltage on the 
check connector.

• Disconnect A-121 engine coolant temperature 

sensor connector.

• Ignition switch: ON

• Voltage between terminal No. 14 and earth.

OK: 4.5 

− 4.9 V

Q: Is the check result normal?

YES : 

Go to Step 6 .

NO : 

Go to Step 7 .

AK402085

1

2

AC

A-121(B)

Connector: A-121

Harness side 

connector

AK402745

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L

AF

A-114

Connector: 

A-114

Harness side connector

Engine-ECU

Battery

AK402085

1

2

AC

A-121(B)

Connector: A-121

Harness side 

connector

Main

Index

Group

TOC

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI) <4G1>

13B-48

STEP 6. Connector check: A-114 engine-ECU 
connector

Q: Is the check result normal?

YES : 

Check and repair harness between A-121 

(terminal No. 1) engine coolant temperature 
sensor connector  and A-114 (terminal No. 
14) engine-ECU connector .

• Check output line for open circuit.

NO : 

Repair or replace.

STEP 7. Connector check: A-114 engine-ECU 
connector

Q: Is the check result normal?

YES : 

Go to Step 8 .

NO : 

Repair or replace.

AK402745

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L

AF

A-114

Connector: 

A-114

Harness side connector

Engine-ECU

Battery

AK402085

1

2

AC

A-121(B)

Connector: A-121

Harness side 

connector

AK402745

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2

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AF

A-114

Connector: 

A-114

Harness side connector

Engine-ECU

Battery

Main

Index

Group

TOC