Mitsubishi Lancer (4A9 engine). Manual - part 299

TROUBLESHOOTING

HEATER, AIR CONDITIONER AND VENTILATION

55A-77

INSPECTION PROCEDURE 14: The PTC heater does not work. <Vehicles with PTC heater>

PTC Heater Circuit

PTC 
HEATER 
RELAY3

PTC 
HEATER 
RELAY1

GLOW 
CONTROL 
RELAY

PTC 
HEATER 
RELAY2

PTC 
HEATER 

A/C-ECU

A/C-ECU

IGNITION
SWITCH (IG1)

ETACS-
ECU

IG1 
RELAY

FUSIBLE
LINK

41

FUSIBLE
LINK

40

FUSIBLE
LINK

39

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

AC612144

AC701453

Connectors: A-23X, A-24X, A-30X, A-32X

A-32X

A-23X

A-24X

AB

A-30X

AC701094

Connector: C-15 <LHD>

AH

C-15 (B)

AC701121

Connectors: C-15, C-127, C-128 <RHD>

AI

C-15 (B)

C-128

C-127 (BR)

AC701093

Connectors: C-52, C-53, C-127, C-128 <LHD>

C-52

C-53

C-127 (BR)

C-128

AM

AC701122 AM

Connectors: C-52, C-53 <RHD>

C-52

C-53

AC701240

AO

Connector: C-317 <LHD>

ETACS-ECU

AC701241

AP

Connector: C-317 <RHD>
ETACS-ECU

TROUBLESHOOTING

HEATER, AIR CONDITIONER AND VENTILATION

55A-78

COMMENTS ON TROUBLE SYMPTOM
If the PTC heater does not work when the following 
conditions are met, the PTC heater, PTC heater 
relay, A/C-ECU, or wiring harness, connector(s) may 
be defective.

• Blower knob: Other than OFF

• The engine is running.

• The engine coolant temperature is 77°C or lower.

• Temperature adjustment knob: MAX HOT

• During low-electric load conditions

PROBABLE CAUSES

• Malfunction of the PTC heater

• Malfunction of the PTC heater relay1

• Malfunction of the PTC heater relay2

• Malfunction of the PTC heater relay3

• Damaged wiring harness or connectors

• Malfunction of the A/C-ECU

DIAGNOSTIC PROCEDURE

STEP 1. M.U.T.-III diagnosis code
Check that the air conditioner has not set a diagnosis 
code.

Q: Is the diagnosis code set?

YES : 

Carry out the diagnosis code procedures. 

Refer to .

NO : 

Go to Step 2.

TROUBLESHOOTING

HEATER, AIR CONDITIONER AND VENTILATION

55A-79

STEP 2. M.U.T.-III other system's diagnosis code
Check that the ETACS-ECU has not set a diagnosis 
code.

Q: Is the diagnosis code set?

YES : 

Carry out the diagnosis code procedures. 

Refer to GROUP 54A, ETACS-ECU .

NO : 

Go to Step 3.

STEP 3. Connector check: A-24X PTC heater 
relay1 connector, A-32X PTC heater relay2 
connector and A-23X PTC heater relay3 
connector

Q: Is the check result normal?

YES : 

Go to Step 4.

NO : 

Repair the connector concerned.

STEP 4. Check the PTC heater relay1, 2 and 3.
Refer to .

Q: Is the check result normal?

YES : 

Go to Step 5.

NO : 

Replace the PTC heater relay1, 2 or 3.

STEP 5. Connector check: C-52 PTC heater 
connector and C-15 A/C-ECU connector

Q: Is the check result normal?

YES : 

Go to Step 6.

NO : 

Repair the connector concerned.

STEP 6. Measure the voltage at C-52 PTC heater 
connector.
(1) Disconnect the connector, and measure at the 

wiring harness side.

(2) Ignition switch: ON
(3) Disconnect A/C-ECU connector C-15 and earth 

terminal 6.

(4) Voltage between terminal 2 and body earth

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 13.

NO : 

Go to Step 7.

STEP 7. Measure the voltage at A-24X PTC heater 
relay1 connector.
(1) Remove the relay, and measure at the relay side.
(2) Voltage between terminal 2 and body earth

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 9.

NO : 

Go to Step 8.

STEP 8. Check the wiring harness between A-24X 
PTC heater relay1 connector terminal No. 2 and 
fusible link (40) connector.
NOTE: Prior to the wiring harness inspection, check 
glow control relay connector A-30X, and repair if nec-
essary.

• Check the power supply line for open circuit.

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 Malfunction ).

NO : 

Repair the wiring harness.

STEP 9. Measure the voltage at A-24X PTC heater 
relay1 connector.
(1) Remove the relay, and measure at the relay side.
(2) Turn the ignition switch to the "ON" earth position.
(3) Voltage between terminal 3 and body earth

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 11.

NO : 

Go to Step 10.

STEP 10. Check the wiring harness between A-
24X PTC heater relay1 connector terminal No. 3 
and C-317 ETACS-ECU connector terminal No. 5.
NOTE: Prior to the wiring harness inspection, check 
intermediate connector C-128, and repair if neces-
sary.

• Check the power supply line for open circuit.

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 Malfunction ).

NO : 

Repair the wiring harness.

STEP 11. Check the wiring harness wires 
between C-52 PTC heater connector terminal No. 
2 and A-24X PTC heater relay1 connector 
terminal No. 4.

• Check the power supply line for open circuit.

Q: Is the check result normal?

YES : 

Go to Step 12.

NO : 

Repair the wiring harness.

TROUBLESHOOTING

HEATER, AIR CONDITIONER AND VENTILATION

55A-80

STEP 12. Check the wiring harness between A-
24X PTC heater relay1 connector terminal No. 1 
and C-15 A/C-ECU connector terminal No. 6.
NOTE: Prior to the wiring harness inspection, check 
intermediate connector C-127, and repair if neces-
sary.

• Check the power supply line for open circuit.

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 Malfunction ).

NO : 

Repair the wiring harness.

STEP 13. Measure the voltage at C-52 PTC heater 
connector.
(1) Disconnect the connector, and measure at the 

wiring harness side.

(2) Ignition switch: ON
(3) Disconnect A/C-ECU connector C-15 and earth 

terminal 7.

(4) Voltage between terminal 3 and body earth

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 20.

NO : 

Go to Step 14.

STEP 14. Measure the voltage at A-32X PTC 
heater relay2 connector.
(1) Remove the relay, and measure at the relay side.
(2) Voltage between terminal 4 and body earth

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 16.

NO : 

Go to Step 15.

STEP 15. Check the wiring harness between A-
32X PTC heater relay2 connector terminal No. 4 
and fusible link (39) connector.

• Check the power supply line for open circuit.

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 Malfunction ).

NO : 

Repair the wiring harness.

STEP 16. Measure the voltage at A-32X PTC 
heater relay2 connector.
(1) Remove the relay, and measure at the relay side.

(2) Turn the ignition switch to the "ON" earth position.
(3) Voltage between terminal 3 and body earth

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 18.

NO : 

Go to Step 17.

STEP 17. Check the wiring harness between A-
32X PTC heater relay2 connector terminal No. 3 
and C-317 ETACS-ECU connector terminal No. 5.
NOTE: Prior to the wiring harness inspection, check 
intermediate connector C-128, and repair if neces-
sary.

• Check the power supply line for open circuit.

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 Malfunction ).

NO : 

Repair the wiring harness.

STEP 18. Check the wiring harness wires 
between C-52 PTC heater connector terminal No. 
3 and A-32X PTC heater relay2 connector 
terminal No. 2.

• Check the power supply line for open circuit.

Q: Is the check result normal?

YES : 

Go to Step 19.

NO : 

Repair the wiring harness.

STEP 19. Check the wiring harness between A-
32X PTC heater relay2 connector terminal No. 1 
and C-15 A/C-ECU connector terminal No. 7.
NOTE: Prior to the wiring harness inspection, check 
intermediate connector C-127, and repair if neces-
sary.

• Check the power supply line for open circuit.

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 Malfunction ).

NO : 

Repair the wiring harness.

STEP 20. Measure the voltage at C-52 PTC heater 
connector.
(1) Disconnect the connector, and measure at the 

wiring harness side.

(2) Ignition switch: ON
(3) Disconnect A/C-ECU connector C-15 and earth 

terminal 5.