Skylark L4-138 2.3L DOHC VIN D MFI (1988)
Wiring Diagram for Coolant Fan Functional Check
CHART C-12C NO LOW SPEED FAN CHECK
Circuit Description:
The electric coolant fan is controlled by the ECM through the low or high speed fan relay based on inputs from the coolant temperature sensor, the A/C
control switch, A/C pressure sensor and the vehicle speed sensor. The ECM controls the coolant fan by grounding CKT 535 (low speed fan relay), or
CKT 536 (high speed fan relay) which turns "ON" the high or low speed fan relays. The low speed fan relay will be turned "ON" when any one of the
following conditions exist:
Code 14 or 15 present.
Coolant temperature 103 degrees C - 106 degrees C or more.
A/C clutch requested and vehicle speed is less than 35 mph.
High speed fan relay will engage regardless of vehicle speed if Code 14 or 15 is not present and one of the following conditions exist:
Coolant temperature 115 degrees C - 118 degrees C or more.
A/C pressure is high.
The coolant fan may be commanded to remain "ON" high speed for up to 7 minutes after the ignition is turned "OFF".
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
1.
Checks for battery voltage at relay harness connector.
2.
Jumpering terminals "1" to "4" bypasses the relay, which should cause the fan to run, if fan motor and wiring to the motor are good.
3.
Grounding the test terminal should cause the ECM to ground CKT 535. At this point, the test light should light, if the ECM is good and CKT 535
isn't open.
4.
This checks for battery voltage and ground to the fan motor. A test light "ON" at this point indicates a faulty fan motor connection, motor
connection, or motor.
