Mitsubishi Lancer (4A9 engine). Manual - part 143

REVERSING SENSOR SYSTEM

CHASSIS ELECTRICAL

54A-234

TROUBLE SYMPTOM CHART

M1547001501133

Trouble symptom

Inspection 
procedure 
number

Reference 
page

The reversing sensor system does not operate.

1

The reversing sensor indicator does not illuminate.

2

The system cannot be activated or deactivated even when the sonar switch is 
pressed.

3

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

4

The reversing sensor indicator keeps flashing.

5

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

6

REVERSING SENSOR SYSTEM

CHASSIS ELECTRICAL

54A-235

SYMPTOM PROCEDURES

Inspection Procedure 1: The reversing sensor system does not operate.

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.)

Reversing Sensor System Power Source Circuit 

ETACS-ECU

POWER 
SOURCE

CORNER SENSOR/
BACK SENSOR-ECU

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)

ACA00886

AL

Connector: C-317
ETACS-ECU

REVERSING SENSOR SYSTEM

CHASSIS ELECTRICAL

54A-236

COMMENTS ON TROUBLE SYMPTOM
If the Reversing sensor system does not work at all 
even when the ignition switch is turned "ON", the 
power supply system, corner sensor/back sensor-
ECU or ETACS-ECU may have a problem.

PROBABLE CAUSES

• Malfunction of corner sensor/back sensor-ECU

• Malfunction of the ETACS-ECU

• Damaged harness wires and connectors

DIAGNOSIS PROCEDURE

STEP 1. Connector check: C-40 corner sensor/
back sensor-ECU connector

Q: Is the check result normal?

YES : 

Go to Step 2.

NO : 

Repair the defective connector.

STEP 2. Voltage measurement at the C-40 corner 
sensor/back sensor-ECU 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-40 corner 

sensor/back sensor-ECU connector (terminal No. 
13) and the body earth.

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 5.

NO : 

Go to Step 3.

STEP 3. Connector check: C-317 ETACS-ECU 
connector

Q: Is the check result normal?

YES : 

Go to Step 4.

NO : 

Repair the defective connector.

STEP 4. Wiring harness check between the C-317 
ETACS-ECU connector (terminal No. 5) and the 
C-40 corner sensor/back sensor-ECU connector 
(terminal No. 13)

• Check the power supply 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 5. Resistance measurement at the C-40 
corner sensor/back sensor-ECU connector
(1) Disconnect the connector, and measure at the 

wiring harness side.

(2) Measure the resistance between the C-40 corner 

sensor/back sensor-ECU connector (terminal No. 
24) and the body earth.

OK: Continuity exists (2 

Ω or less)

Q: Is the check result normal?

YES : 

Go to Step 7.

NO : 

Go to Step 6.

STEP 6. Wiring harness check between the C-40 
corner sensor/back sensor-ECU connector 
(terminal No. 24) 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 7. Replace the corner sensor/back sensor-
ECU temporarily, and then check the trouble 
symptom.
Replace the corner sensor/back sensor-ECU tempo-
rarily, then check if the corner sensors operate.

Q: Is the check result normal?

YES : 

Replace the corner sensor/back sensor-

ECU.

NO : 

Replace the ETACS-ECU.

REVERSING SENSOR SYSTEM

CHASSIS ELECTRICAL

54A-237

Inspection Procedure 2: The reversing sensor indicator does not illuminate.

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.)

Sonar Switch Indicator Circuit 

CORNER SENSOR/
BACK SENSOR-ECU

SONAR SWITCH

ETACS-ECU

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)