Symptom:
*BLOWER MOTOR ALWAYS RUNS AT ONE SPEED ONLY
POSSIBLE CAUSES
BLOWER MOTOR CONTROL CKT SHORTED TO GROUND
BLOWER MOTOR CONTROL CIRCUIT SHORTED TO BLOWER MOTOR HIGH DRIVER CIRCUIT
AZC MODULE, FAN STUCK ON ONE SPEED ONLY
BLOWER MOTOR CONTROLLER
TEST
ACTION
APPLICABILITY
1
Turn the ignition off.
Disconnect the Blower Motor Controller harness connector.
Disconnect the AZC module C2 harness connector.
Measure the resistance between ground and the Blower Motor Control circuit.
Is the resistance below 5.0 ohms?
All
Yes
→
Repair the Blower Motor Control circuit for a short to ground.
Perform BODY VERIFICATION TEST - VER 1.
No
→
Go To
2
2
Turn the ignition off.
Disconnect the Blower Motor Controller harness connector.
Disconnect the Blower Motor harness connector.
Measure the resistance between the Blower Motor Control circuit and the Blower
Motor High Driver circuit.
Is the resistance below 5.0 ohms?
All
Yes
→
Repair the Blower Motor Control circuit for a short to the Blower
Motor High Driver circuit.
Perform BODY VERIFICATION TEST - VER 1.
No
→
Go To
3
3
Turn the ignition off. Reconnect all previous disconnected components.
Use the DRB oscilloscope, select Lab Scope and set the following lab scope parame-
ters. Set voltage range to +10.0v. Set probe to X10. Set time to 20ms/Div.
Using the oscilloscope lead, backprobe the Blower Motor Control circuit at the Blower
Motor Controller harness connector.
Turn the ignition on.
Set the blower switch to LO then slowly move to HI while observing the DRB display.
The Scope patten should appear similar to what is provided in the reference material
(Section 8.0). The voltage should cycle from approximately 0.5 volts, up to 5.0 volts in
the low speed fan position.
The duty cycle pattern should change smoothly as the blower switch is turned from
LO to HI. The pattern should completely flatline when the blower speed reaches the
HI setting.
Does the DRB display a duty cycle pattern that changes from approximately 0.5 to
5.0 volts in LO?
All
Yes
→
Go To
4
No
→
Replace the AZC Module.
Perform BODY VERIFICATION TEST - VER 1.
NOTE: With the DRB, Reset Module after repair/replacement is completed.
339
HEATING & A/C