Inspection Procedure 26: PTC Heater Relay System <Vehicles with PTC Heater>


OPERATION
With the engine and blower motor being operated, if the PTC heater does not operate by setting the heater control to MAX HOT at the coolant temperature of 75 °C or lower, the PTC heater, PTC heater relay, engine-ECU or its circuit system may be faulty.

PROBABLE CAUSES

  • Failed PTC heater
  • Failed PTC heater relay A
  • Failed PTC heater relay B
  • Failed PTC heater relay C
  • Open/short circuit or harness damage in PTC heater relay circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III data list

  • Refer to Data List Reference Table .

    1. Item 76: PTC heater relay 1
    2. Item 77: PTC heater relay 2

Q. Is the check result normal?
Go to Step 3.
Go to Step 2.

STEP 2. Perform voltage measurement at engine-ECU connector.

  • Disconnect connector, and measure at the harness side.
  • Ignition switch: ON
  • Voltage between terminal HTR1, HTR2, HTR3 and body earth.
OK: System voltage

Q. Is the check result normal?
Go to Step 3.
Repair or replace the connector, or check and repair harness between engine-ECU connector terminal HTR1, HTR2, HTR3 and PTC heater relay A, PTC heater relay B, PTC heater relay C connector terminal, ignition switch (IG2) connector terminal, IG2 relay connector terminal.

STEP 3. Check PTC heater relay.

  • PTC heater relay connector check.
  • Check PTC heater relay (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - Relay Check).

Q. Is the check result normal?
Go to Step 4.
Repair or replace the connector, or replace the PTC heater relay.

STEP 4. Perform voltage measurement at PTC heater connector.

  • Disconnect connector, and measure at the harness side.
  • Using a jumper wire, connect engine-ECU connector terminal HTR1, HTR2, HTR3 and body earth.
  • Ignition switch: ON
  • Voltage between PTC heater connector power supply line terminal 1, 2, 3 and body earth.
OK: System voltage

Q. Is the check result normal?
Go to Step 7.
Go to Step 5.

STEP 5. Check harness between PTC heater relay A, PTC heater relay B, PTC heater relay C connector terminal and PTC heater connector terminal.

  • Check output line for open/short circuit.

Q. Is the check result normal?
Go to Step 6.
Repair or replace the connector, or repair the damaged harness wire.

STEP 6. Check harness between fusible link and PTC heater relay A, PTC heater relay B, PTC heater relay C connector terminal.

  • Check power supply line for damage.

Q. Is the check result normal?
Go to Step 7.
Repair or replace the connector, or repair the damaged harness wire.

STEP 7. Check the trouble symptom
Check that the PTC heater works normally.

Q. Is the check result normal?
This diagnosis is complete.
Replace the PTC heater. Then go to Step 8.

STEP 8. Check the trouble symptom
Check that the PTC heater works normally.

Q. Is the check result normal?
This diagnosis is complete.
Replace the engine-ECU.