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Inspection Procedure 30: Blower Fan Signal System <Manual A/C>
 
 
 
 
CIRCUIT OPERATION
  • The air volume stage 3 terminal in the blower switch connector sends voltage signal according to the blower switch position (OFF, 1, 2, 3 or 4) to the ECM connector terminal BFAN.
 
 
 
COMMENT
  • The ECM adjusts voltage, which the generator generated, according to the blower switch position.
 
 
 
PROBABLE CAUSES
  • Failed blower switch
  • Open/short circuit or harness damage in blower circuit or loose connector contact
  • Open/short circuit or harness damage in blower switch position signal circuit or loose connector contact
  • Failed ECM
 
 
 
 
DIAGNOSIS
Required Special Tools:
  • MB992744: Vehicle communication interface-Lite (V.C.I.-Lite)
  • MB992745: V.C.I.-Lite main harness A
  • MB992747: V.C.I.-Lite USB cable short
  • MB992748: V.C.I.-Lite USB cable long
  • MB991958: Scan Tool (M.U.T.-III Sub Assembly)
    • MB991824: Vehicles Communication Interface (V.C.I.)
    • MB991827: M.U.T.-III USB Cable
    • MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)
STEP 1. Using scan tool (M.U.T.-III), check data list.
cautionTo prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
(1) Connect scan tool (M.U.T-III). Refer to HOW TO CONNECT THE SCAN TOOL (M.U.T.-III) .
(2) Turn the ignition switch to the "ON" position.
(3) Check the following item in the data list. Refer to Data List Reference Table .
  1. Item 176: Blower fan signal
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the blower switch condition normal?
It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .
Go to Step 2.
 
STEP 2. Measure the sensor output voltage at ECM connector by backprobing.
(1) Do not disconnect the connector.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal BFAN line and ground by backprobing.
  • Voltage should be battery positive voltage when blower switch is OFF position.
  • Voltage should be between 3 and 9 volts when blower switch position is "1" or "2".
  • Voltage should be 1 volt or less when blower switch position is "3" or "4".
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the measured voltage normal?
Go to Step 4.
Go to Step 3.
 
STEP 3. Check of open circuit, short circuit, and damage in BFAN line between ECM connector and blower switch connector.
Is the check result normal?
Go to Step 4.
Repair the connector(s) or wiring harness.
 
STEP 4. Check the blower function..
The blower speed should correspond to the blower switch position.
Is the blower operating properly?
Go to Step 5.
Check the blower-related circuit (Refer to GROUP 55A - Troubleshooting - Trouble symptom Chart ).
 
STEP 5. Using scan tool (M.U.T.-III), check data list.
(1) Turn the ignition switch to the "ON" position.
(2) Check the following item in the data list. Refer to Data List Reference Table .
  1. Item 176: Blower fan signal
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the switch condition normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
Replace the ECM.