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
1 2
19
21
20
18
17
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14
1213
11
8 9
L
10
37
52 53 54 555657585960616263646566
38 39 404142434445464748495051
22 23 24 252627282930313233343536
7
5
3
1
6
4
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
).
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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4
2
5
3
1
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66
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
6
4
2
5
3
1
9
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65
66
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
6
4
2
5
3
1
9
7
8
10
11
12
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14
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54
55
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57
58
59
60
61
62
63
64
65
66
L
AF
A-114
Connector:
A-114
Harness side connector
Engine-ECU
Battery
Main
Index
Group
TOC
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