Protege L4-1839cc 1.8L DOHC (1990)
Electric Load Signal: Testing and Inspection
Electrical load signals (component "ON") are sent to the ECU from the headlight switch, blower motor switch, cooling fan switch and rear window
defroster switch.
HEADLIGHT SWITCH
Headlight switch signal can be checked at ECU terminal 1U. With headlights "ON," terminal voltage should be approximately 12V. With headlights
"OFF," voltage should be below 1.0V. If headlight operation is okay but terminal voltage is always below 1.0V, check for short or open circuit in wiring
from headlight relay to ECU terminal 1U.
BLOWER MOTOR SWITCH
Blower motor switch signal can be checked at ECU terminal 1S, ignition "ON." With blower switch "OFF" or in 1st position, terminal voltage should be
approximately 12V. With switch "ON" in 2nd or higher position, voltage should be below 1.0V. If blower motor operation is okay but terminal voltage
is always below 1.0V, check for short in wiring from blower switch to ECU terminal 1S, bad connection at ECU connector or ECU malfunction. If
blower motor operation is okay but terminal voltage is always approximately 12V, check for open circuit in wiring from blower switch to ECU terminal
1S.
COOLING FAN SWITCH
Cooling fan switch signal can be checked at ECU terminal 1R with engine running. With fan operating or diagnosis connector terminal TFA grounded,
terminal voltage should be below 1.0V. With engine idling and fan "OFF," terminal voltage should be approximately 12V. If cooling fan operation is
okay but terminal voltage is always below 1.0V, check for open or short circuit in wiring from fan relay to ECU terminal 1R or ECU malfunction.
REAR WINDOW DEFROSTER SWITCH
Rear window defroster switch signal can be checked at ECU terminal 1T, ignition "ON." With defroster switch "OFF," terminal voltage should be
below 1.0V. With switch "ON," voltage should be approximately 12V. If defroster switch indicator lamp lights when switch is "ON" (normal operation)
but terminal voltage is always below 1.0V, check for open or short circuit in wiring from defroster switch to ECU terminal 1T. If indicator lamp never
lights, check for open circuit in wiring from ignition switch to defroster switch or defroster switch malfunction.
