Mitsubishi Lancer (4A9 engine). Manual - part 144

REVERSING SENSOR SYSTEM

CHASSIS ELECTRICAL

54A-238

COMMENTS ON TROUBLE SYMPTOM
If the reversing indicator does not illuminate, the wir-
ing harness, connectors, corner sensor/back sensor-
ECU, or ETACS-ECU may be defective.

PROBABLE CAUSES

• Damaged harness wires and connectors

• Malfunction of corner sensor/back sensor-ECU

• Malfunction of the ETACS-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: C-43 sonar switch 
connector

Q: Is the check result normal?

YES : 

Go to Step 2.

NO : 

Repair the defective connector.

STEP 2. Sonar switch check
Check the indicator. (Refer to )

Q: Is the check result normal?

YES : 

Go to Step 3.

NO : 

Replace the sonar switch.

STEP 3. M.U.T.-III other system diagnosis code
Check if the diagnosis code is set to the ETACS-
ECU.

Q: Is the check result normal?

YES : 

Troubleshoot the ETACS-ECU. Refer to 

ETACS-ECU 

− Troubleshooting .

NO : 

Go to Step 4.

STEP 4. Voltage measurement at the C-43 sonar 
switch connector
(1) Disconnect the connector, and measure at the 

wiring harness side.

(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between the C-43 sonar 

switch connector (terminal No. 5) and the body 
earth.

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 6.

NO : 

Go to Step 5.

STEP 5. Wiring harness check from C-317 
ETACS-ECU connector (terminal No.5) to C-43 
sonar switch connector (terminal No. 5)

• Check the communication line for open circuit or 

short circuit.

NOTE: Before the wiring harness inspection, inspect 
joint connector C-150, and repair if necessary.

Q: Is the check result normal?

YES : 

Troubleshoot the ETACS-ECU. Refer to 

Inspection Procedure 2 "The ignition switch 
(IG1) signal is not received" .

NO : 

Repair the wiring harness.

STEP 6. Connector check: C-40 corner sensor/
back sensor-ECU connector

Q: Is the check result normal?

YES : 

Go to Step 7.

NO : 

Repair the defective connector.

STEP 7. Wiring harness check from C-43 sonar 
switch connector (terminal No. 6) to C-40 corner 
sensor/back sensor-ECU connector (terminal No. 
11).

• Check the communication line for open circuit or 

short circuit.

Q: Is the check result normal?

YES : 

Go to Step 8.

NO : 

Repair the wiring harness.

STEP 8. Retest the system

Q: Is the check result normal?

YES : 

The diagnosis is complete.

NO : 

Replace the corner sensor/back sensor-
ECU.

ACA00886

AL

Connector: C-317
ETACS-ECU

REVERSING SENSOR SYSTEM

CHASSIS ELECTRICAL

54A-239

Inspection Procedure 3: The system cannot be activated or deactivated even when the sonar switch 
is pressed.

CAUTION

• Whenever the ECU is replaced, ensure that the input signal circuit is normal.
• When the illuminated licence plate is installed, the sensors may not operate because of noise from 

the plate. (When the ultrasonic noise is received, the bass toned buzzer sound continuously. 
When the ultrasonic noise stops, the normal operation will be resumed immediately.)

COMMENTS ON TROUBLE SYMPTOM
If the reversing sensor system ON/OFF cannot be 
switched even when the sonar switch is pressed, the 
harness, connector(s), sonar switch, or corner sen-
sor/back sensor-ECU may have a problem.

PROBABLE CAUSES

• Damaged harness wires and connectors

• Malfunction of sonar switch

• Malfunction of corner sensor/back sensor-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: C-43 sonar switch 
connector

Q: Is the check result normal?

YES : 

Go to Step 2.

NO : 

Repair the defective connector.

Sonar Switch Circuit 

CORNER SENSOR/
BACK SENSOR-ECU

SONAR SWITCH

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

AC612705

Connector: C-40

DQ

C-40 (B)

AC801266

AJ

Connector: C-43

C-43 (L)

REVERSING SENSOR SYSTEM

CHASSIS ELECTRICAL

54A-240

STEP 2. sonar switch check
Inspect the corner sensor switch for normal opera-
tion. (Refer to )

Q: Is the check result normal?

YES : 

Go to Step 3.

NO : 

Replace the sonar switch.

STEP 3. Resistance measurement at the C-43 
sonar switch connector
(1) Disconnect the connector, and measure at the 

wiring harness side.

(2) Measure the resistance between the C-43 sonar 

switch connector (terminal No. 2) and the body 
earth.

OK: Continuity exists (2 

Ω or less)

Q: Is the check result normal?

YES : 

Go to Step 5.

NO : 

Go to Step 4.

STEP 4. Wiring harness check between the C-43 
sonar switch connector (terminal No. 2) and the 
body earth

• Check the earth wires for open circuit.

Q: Is the check result normal?

YES : 

Retest the system.

NO : 

Repair the wiring harness.

STEP 5. Connector check: C-40 corner sensor/
back sensor-ECU connector

Q: Is the check result normal?

YES : 

Go to Step 6.

NO : 

Repair the defective connector.

STEP 6. Wiring harness check between the C-43 
sonar switch connector (terminal No. 1) and the 
C-40 corner sensor/back sensor-ECU connector 
(terminal No. 2)

• Check the communication line for open circuit or 

short circuit.

Q: Is the check result normal?

YES : 

Replace the corner sensor/back sensor-

ECU.

NO : 

Repair the wiring harness.

Inspection Procedure 4: One or more of the reversing sensor (corner sensor/back sensor) does not 
detect the obstacle.

 

Inspection Procedure 5: The reversing sensor indicator keeps flashing.

CAUTION

• Whenever the ECU is replaced, ensure that 

the input signal circuit is normal.

• When the illuminated licence plate is 

installed, the sensors may not operate 
because of noise from the plate. (When the 
ultrasonic noise is received, the bass toned 
buzzer sound continuously. When the ultra-
sonic noise stops, the normal operation will 
be resumed immediately.)

COMMENTS ON TROUBLE SYMPTOM
If one or more of the reversing sensors (corner sen-
sor/back sensor) cannot detect obstacles, the wires 
and connectors, reversing sensors (corner sensor/
back sensor), or the corner sensor/back sensor-ECU 
may have abnormalities. Also, if one or more of the 
sensors has an abnormality (open circuit, malfunc-
tion, etc.), the corner sensor/back sensor-ECU 
informs the abnormality by making the reversing sen-
sor indicator flash.

NOTE: 

.

•

If the corner sensor/back sensor-ECU detects an 
abnormality (open circuit, malfunction, etc.) with 
one or more of the sensors, it turns off the rele-
vant sensor and sounds the high toned buzzer for 
5 seconds. The reversing sensor indicator illumi-
nates while the system is being operated until the 
relevant sensor returns to normal.

•

If ultrasonic noise is received with one or more of 
the sensor, the corner sensor/back sensor-ECU 
sounds the low toned buzzer continuously. When 
the ultrasonic noise is stopped, the sensor 
returns to normal. (The reversing sensor indicator 
does not flash.)

PROBABLE CAUSES

• Damaged harness wires and connectors

• Malfunction of reversing sensor (corner sensor/

back sensor)

• Malfunction of corner sensor/back sensor-ECU

REVERSING SENSOR SYSTEM

CHASSIS ELECTRICAL

54A-241

DIAGNOSIS PROCEDURE

STEP 1. Check the reversing sensor (corner 
sensor/back sensor) for interference.

Q: Are there anything that interferes with the 

communication (things that generate radio waves 
such as magnets and an air-cleaning device that 
has a power plug) near the reversing sensor 
(corner sensor/back sensor)?
YES : 

Move away or remove things that interfere 

with the communication (things that 
generate radio waves such as magnets and 
a air-cleaning device that has a power plug) 
near the reversing sensor (corner sensor/
back sensor).

NO : 

Go to Step 2

STEP 2. M.U.T.-III diagnosis code
Check if diagnosis code is set to the reversing sen-
sor (corner sensor/back sensor).

Q: Is the diagnosis code set?

YES : 

Refer to .

NO : 

Go to Step 3.

STEP 3. Trouble symptom recheck

Q: Is the check result normal?

YES : 

The trouble can be an intermittent 

malfunction (Refer to GROUP 00 

− How to 

use Troubleshooting/inspection Service 
Points 

− How to Cope with Intermittent 

Malfunction ).

NO : 

Replace the corner sensor/back sensor-
ECU.

Inspection Procedure 6: Obstacle is not detected even when the selector or shift lever is shifted to 
"R" (Reverse) position.

CAUTION

• Whenever the ECU is replaced, ensure that the input signal circuit is normal.
• When the illuminated licence plate is installed, the sensors may not operate because of noise from 

the plate. (When the ultrasonic noise is received, the bass toned buzzer sound continuously. 
When the ultrasonic noise stops, the normal operation will be resumed immediately.)

ACB02649

AB

Connectors: B-109, B-110 
<1600>

B-109 (B)

B-110 (B)

ACB02651

AB

Connectors: B-109, B-110 
<1800-petrol-SOHC>

B-109 (B)

B-110 (B)

ACB02653

AB

B-109 (B)

B-110 (B)

Connectors: B-109, B-110 
<1800-petrol-DOHC, 2000>

AC809223

AC

Connector: B-110 <DIESEL>

B-110 (B)