DTC Troubleshooting: B1234 (B and A/C ON)
DTC B1234 or DTC indicator B and A/C ON:
 A Short in the Driver's Air Mix Control Motor Circuit
  1. Clear the DTC with the HDS.
  1. Turn the ignition switch to LOCK (0) and then to ON (II).
  1. Check for DTCs.
Is DTC B1234 or B and A/C ON indicated?
YES -
Go to Step 5 .
NO -
Intermittent failure.■
  1. Check for DTCs.
Are these DTCs also present; B121B or H and A/C ON, and/or B1220 or L and A/C ON, and/or B1237 or E and A/C ON?
YES -
Go to Step 13 .
NO -
Go to Step 6 .
  1. Turn the ignition switch to LOCK (0).
Is the driver's air mix control motor OK?
YES -
Go to Step 8 .
NO -
  1. Disconnect the driver's air mix control motor 7P connector.
  1. Disconnect heater control unit connectors A (28P) and B (12P).
  1. Check for continuity between body ground and heater control unit connector A (28P) No. 14 terminal.
Is there continuity?
YES -
Repair short to body ground in the wire between the heater control unit and the driver's air mix control motor.■
NO -
Go to Step 11 .
  1. Check for continuity between heater control unit connector A (28P) No. 14 terminal and heater control unit connector B (12P) No. 12 terminal.
Is there continuity?
YES -
Repair short in the wires.■
NO -
Go to Step 12 .
  1. Turn the ignition switch to ON (II), and measure the voltage between heater control unit connector A (28P) No. 14 terminal and body ground.
Is there any voltage?
YES -
Repair short to power in the wire between the heater control unit and the driver's air mix control motor. This short may also damage the heater control unit. Repair short to power before replacing the heater control unit.■
NO -
Substitute a known-good heater control unit, and recheck. If the symptom/indication goes away, replace the original heater control unit .■
  1. Turn the ignition switch to LOCK (0), and disconnect heater control unit connector B (12P).
  1. Disconnect these items:
    • Driver's air mix control motor
    • Passenger's air mix control motor
    • Recirculation control motor
    • Mode control motor
  1. Check for continuity between heater control unit connector B (12P) No. 12 terminal and body ground.
Is there continuity?
YES -
Repair short to body ground in the wire.■
NO -
Go to Step 16 .
  1. Turn the ignition switch to ON (II), and check the same terminal for voltage to body ground.
Is there any voltage?
YES -
Repair short to power in the wire. This short may have also damaged the heater control unit. Repair short to power before replacing the heater control unit.■
NO -
Go to Step 17 .
  1. Turn the ignition switch to LOCK (0).
  1. Reconnect heater control unit connector B (12P).
  1. Turn the ignition switch to ON (II), and measure the voltage between heater control unit connector B (12P) No. 12 terminal and body ground.
Is there about 5 V?
YES -
Go to Step 20 .
NO -
Check for a loose wire or poor connection at heater control unit connector B (12P). If the connection is good, substitute a known-good heater control unit and recheck. If the symptom/indication goes away, replace the original heater control unit .■
  1. While checking the same terminal for voltage to ground, reconnect these items individually and note the voltage reading each time:
    • Driver's air mix control motor
    • Passenger's air mix control motor
    • Recirculation control motor
    • Mode control motor
Does the voltage remain at about 5 V?
YES -
Substitute a known-good heater control unit and recheck. If the symptom/indication goes away, replace the original heater control unit .■
NO -
Replace the component that caused the voltage drop.■