Mitsubishi Lancer Evolution IX. Manual - part 398

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-67

STEP 16. Connector check: C-119 engine-ECU 
connector

Q: Is the check result normal?

YES : 

Check and repair harness between B-03 

(terminal No. 4) throttle position sensor 
connector and C-119 (terminal No. 49) 
engine-ECU connector.

• Check earthing line for damage.

NO : 

Repair or replace the connector.

STEP 17. Perform voltage measurement at B-03 
throttle position sensor connector.

• Use special tool test harness (MB991536) to con-

nect connector, and measure at pick-up harness.

• Ignition switch: "ON"

• Voltage between terminal No. 2 and earth.

OK:

Accelerator pedal fully released: 0.536 

− 0.735 

V

Accelerator pedal fully depressed: 4.5 

− 5.0 V

Q: Is the check result normal?

YES : 

Go to Step 20 .

NO : 

Go to Step 18 .

STEP 18. Adjust throttle position sensor

• Adjust throttle position sensor (Refer to 

P.13A-395

).

Q: Is the adjusted value normal?

YES : 

Go to Step 19 .

NO : 

Adjust throttle position sensor.

AK501994

65

43
50

42
49

41
48
60

61

64

46

47

58

59

67

68

45

56
66

52 51

44

53

62

54

63

57

55

AB

Connector: C-119

C-119 (GR)

C-119 (GR)

Harness side connector

<L. H. drive vehicles>

<R. H. drive vehicles>

AK305010

2 1

3

4

AB

Connector : B-03

Harness side 
connector

B-03(B)

AK305010

2 1

3

4

AB

Connector : B-03

Harness side 
connector

B-03(B)

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-68

STEP 19. Connector check: C-117 engine-ECU 
connector

Q: Is the check result normal?

YES : 

Check and repair harness between B-03 

(terminal No. 2) throttle position sensor 
connector and C-117 (terminal No. 78) 
engine-ECU connector.

• Check output line for short circuit and 

damage.

NO : 

Repair or replace the connector.

STEP 20. Perform voltage measurement at C-117 
engine-ECU connector

• Measure engine-ECU terminal voltage.

• Ignition switch: "ON"

• Voltage between terminal No. 78 and earth.

OK:

Accelerator pedal fully released: 0.536 

− 0.735 

V

Accelerator pedal fully depressed: 4.5 

− 5.0 V

Q: Is the check result normal?

YES : 

Go to Step 22 .

NO : 

Go to Step 21 .

AK501996

80

87

81

94

85

82

84

93

86

98

99

74

92

73

83

88

91

95

97 96

100

89

78

71

90

76

77

75

72
79

AB

Connector: C-117

C-117 (GR)

C-117 (GR)

Harness side connector

<L. H. drive vehicles>

<R. H. drive vehicles>

AK305010

2 1

3

4

AB

Connector : B-03

Harness side 
connector

B-03(B)

AK501996

80

87

81

94

85

82

84

93

86

98

99

74

92

73

83

88

91

95

97 96

100

89

78

71

90

76

77

75

72
79

AB

Connector: C-117

C-117 (GR)

C-117 (GR)

Harness side connector

<L. H. drive vehicles>

<R. H. drive vehicles>

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-69

STEP 21. Connector check: C-117 engine-ECU 
connector

Q: Is the check result normal? 

YES : 

Check and repair harness between B-03 

(terminal No. 2) throttle position sensor 
connector and C-117 (terminal No. 78) 
engine-ECU connector.

• Check output line for open circuit and 

damage.

NO : 

Repair or replace the connector.

STEP 22. Connector check: C-117 engine-ECU 
connector

Q: Is the check result normal?

YES : 

Go to Step 9 .

NO : 

Repair or replace the connector.

AK501996

80

87

81

94

85

82

84

93

86

98

99

74

92

73

83

88

91

95

97 96

100

89

78

71

90

76

77

75

72
79

AB

Connector: C-117

C-117 (GR)

C-117 (GR)

Harness side connector

<L. H. drive vehicles>

<R. H. drive vehicles>

AK305010

2 1

3

4

AB

Connector : B-03

Harness side 
connector

B-03(B)

AK501996

80

87

81

94

85

82

84

93

86

98

99

74

92

73

83

88

91

95

97 96

100

89

78

71

90

76

77

75

72
79

AB

Connector: C-117

C-117 (GR)

C-117 (GR)

Harness side connector

<L. H. drive vehicles>

<R. H. drive vehicles>

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-70

Code No. P0125: Feedback system monitor

OPERATION

• Refer to P0201 injector circuit 

P.13A-105

.

Refer to P0202 injector circuit 

P.13A-111

.

Refer to P0203 injector circuit 

P.13A-117

.

Refer to P0204 injector circuit 

P.13A-123

.

• Refer to P0130 Oxygen sensor (front) circuit 

P.13A-75

.

FUNCTION

• The engine-ECU effects air-fuel ratio feedback 

control in accordance with the signals from the 
oxygen sensor (front).

• If the heated oxygen sensor (front) has deterio-

rated, corrections will be made by the oxygen 
sensor (rear).

• Diagnosis code P0125 becomes stored in mem-

ory if a failure is detected in the above air-fuel 
ratio feedback control system.

TROUBLE JUDGMENT

Check Conditions

• The engine coolant temperature is approximately 

76

°C or more.

• Within the range of air-fuel ratio feedback opera-

tion.

• Not in slowing down operation.

Judgment Criterion

• The oxygen sensor output voltage is not deviated 

from 0.5 V for 30 seconds.

PROBABLE CAUSES

• Failed oxygen sensor (front)

• Harness damage in oxygen sensor (front) circuit 

or loose connector contact

• Failed oxygen sensor (rear)

NOTE: When the oxygen sensor (front) begins to 
deteriorate, the oxygen sensor output voltage will 
deviate from the voltage when the sensor was new 
(normally 0.5 volt at stoichiometric ratio). This devia-
tion will be corrected by the oxygen sensor (rear). If 
the oxygen sensor (rear) responds poorly because it 
has deteriorated, it will improperly correct the oxygen 
sensor (front). Thus, even when closed loop control 
is being effected, the fluctuation of the oxygen sen-
sor (front) output voltage decreases, without inter-
secting with 0.5 volt. As a result, there is a possibility 
of diagnosis code P0125 becoming registered.

• Failed fuel system

• Failed exhaust system

• Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-II/III diagnosis code

Q: Is any other diagnosis code than P0125 output?

YES : 

Inspection chart for diagnosis code (Refer 

to 

P.13A-17

).

NO : 

Go to Step 2 .

STEP 2. M.U.T.-II/III data list

• Refer to Data List Reference Table 

P.13A-372

.

a. Item No. 12: Air flow sensor
b. Item No. 21: Engine coolant temperature sensor

c. Item No. 25: Barometric pressure sensor

d. Item No. 59: Oxygen sensor (rear)

Q: Are the check results normal?

YES : 

Go to Step 3 .

NO : 

Perform the diagnosis code classified check 
procedure for the sensor that has shown an 
abnormal data valve (Refer to Inspection 
Chart for Diagnosis Codes 

P.13A-17

).

STEP 3. Check for intake of air from intake hose 
and inlet manifold.

Q: Is the check result normal?

YES : 

Go to Step 4 .

NO : 

Repair.

STEP 4. Check for leakage of exhaust emission 
from exhaust manifold.

Q: Is the check result normal?

YES : 

Go to Step 5 .

NO : 

Repair.

STEP 5. Check throttle body (throttle valve 
portion) for contamination. 

Q: Is the check result normal?

YES : 

Go to Step 6 .

NO : 

Clean throttle body (throttle valve portion) 
(Refer to 

P.13A-395

).