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INSPECTION PROCEDURE 11: Heater controller assembly (A/C-ECU) power supply system
 
 
 
 
TECHNICAL DESCRIPTION (COMMENT)
If the heater controller assembly (A/C-ECU) is not energized, the power supply or ground system to the ECU may be defective.
 
 
 
TROUBLESHOOTING HINTS
  • Malfunction of the heater controller assembly (A/C-ECU)
  • The wiring harness or connectors may have loose, corroded, or damaged terminals, or terminals pushed back in the connector
 
 
 
DIAGNOSIS
Required Special Tools:
  • MB991223: Harness Set
  • MB992006: Extra Fine Probe
STEP 1. Using scan tool (M.U.T.-IIISE), check whether the other system DTC is set.
Check that the ETACS-ECU has not set a DTC.
(1)
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn the electric motor switch to the OFF position before connecting or disconnecting scan tool (M.U.T.-IIISE).
Connect scan tool (M.U.T.-IIISE). Refer to "How to connect the Scan Tool (M.U.T.-IIISE) ".
(2) Turn the electric motor switch from OFF position to ON position.
(3) Check if DTC is set.
(4) Turn the electric motor switch to the OFF position.
Is the DTC set?
Carry out the diagnostic trouble code procedures (Refer to GROUP 54A - ETACS-ECU, diagnostic trouble code chart ).
Go to Step 2.
 
STEP 2. Measure the voltage at the heater controller assembly (A/C-ECU) connector.
(1) Disconnect the connector, and measure at the wiring harness side.
(2) Power supply mode of the electric motor switch: OFF → ON
(3) Voltage between IG1 terminal and body ground
OK: The voltage should measure approximately 12 volts (battery positive voltage).
Is the check result normal?
Go to Step 4.
Go to Step 3.
 
STEP 3. Check of open circuit in IG1 line between ETACS-ECU connector and heater controller assembly (A/C-ECU) connector.
Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
Repair the connector(s) or wiring harness.
 
STEP 4. Measure the voltage at the heater controller assembly (A/C-ECU) connector.
(1) Disconnect the connector, and measure at the wiring harness side.
(2) Voltage between B/UP terminal and body ground.
OK: The voltage should measure approximately 12 volts (battery positive voltage).
Is the check result normal?
Go to Step 6.
Go to Step 5.
 
STEP 5. Check of open circuit in B/UP line between ETACS-ECU connector and heater controller assembly (A/C-ECU) connector.
Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
Repair the connector(s) or wiring harness.
 
STEP 6. Measure the resistance at the heater controller assembly (A/C-ECU) connector.
(1) Disconnect the connector, and measure at the wiring harness side.
(2) Resistance between E terminal and body ground
OK: The resistance should be 2 ohms or less
Is the check result normal?
Replace the heater controller assembly (A/C-ECU) (Refer to ).
Go to Step 7.
 
STEP 7. Check of open circuit in E line between heater controller assembly (A/C-ECU) connector and ground J/C (DASH) connector.
Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction ).
Repair the connector(s) or wiring harness.