MTC 85
85-BLOWER NOT ON HIGH DURING COOLDOWN TEST (MTC)85 - Blower Not On High During Cooldown Test (MTC):
WHEN MONITORED
When executing the Cooldown Test.
SET CONDITION
If the A/C Heater Control sensed that the blower was not operating at high speed while the Cooldown Test was running.
POSSIBLE CAUSES
- Blower control did not remain on the high speed setting during the entire cooldown test
- Blower motor / related circuits
- (C850) Blower switch position signal circuit shorted to (Z908) ground circuit
- (C850) Blower switch position signal circuit shorted to (Z909) ground circuit
- (C850) Blower switch position signal circuit shorted to ground
- (C850) Blower switch position signal circuit open
- A/C heater control
NOTE: This DTC will display as active if the ignition is not cycled after running the Cooldown Test. Otherwise, it will display as stored until cleared.
DIAGNOSTIC TEST
1. CHECK THE BLOWER SPEED SETTING
Q: Was the blower control set to high speed for the entire Cooldown Test?
YES: Go To 2
NO: Start the engine, set the blower control to high speed, and then run the Cooldown Test again.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
2. CHECK THE (C850) BLOWER SWITCH POSITION SIGNAL CIRCUIT FOR A SHORT TO THE (Z908) GROUND CIRCUIT
Turn the ignition off.
Disconnect the A/C Heater Control C3 harness connector.
Measure the resistance between the (C850) Blower Switch Position Signal circuit and the (Z908) Ground circuit in the A/C Heater Control C3 harness connector.
Q: Is the resistance below 10K ohms?
YES: Repair the (C850) Blower Switch Position Signal circuit for a short to the (Z908) Ground circuit. Run the Cooldown Test again after the repair is complete.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 3
3. CHECK THE (C850) BLOWER SWITCH POSITION SIGNAL CIRCUIT FOR A SHORT TO THE (Z909) GROUND CIRCUIT
Disconnect the A/C Heater Control C1 harness connector.
Measure the resistance between the (C850) Blower Switch Position Signal circuit and the (Z909) Ground circuit in the A/C Heater Control C1 harness connector.
Q: Is the resistance below 10K ohms?
YES: Repair the (C850) Blower Switch Position Signal circuit for a short to the (Z909) Ground circuit. Run the Cooldown Test again after the repair is complete.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 4
4. CHECK THE (C850) BLOWER SWITCH POSITION SIGNAL CIRCUIT VOLTAGE
Reconnect the A/C Heater Control C1 harness connector.
Turn the ignition on.
Measure the voltage of the (C850) Blower Switch Position Signal circuit.
Q: Is the voltage above 4.8 volts?
YES: Check the blower motor and related circuits for the cause of blower operation problems and repair as necessary. Run the Cooldown Test again after the repair is complete.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 5
5. CHECK THE (C850) BLOWER SWITCH POSITION SIGNAL CIRCUIT FOR A SHORT TO GROUND
Measure the resistance of the (C850) Blower Switch Position Signal circuit between ground and the A/C Heater Control C3 harness connector.
Q: Is the resistance below 10K ohms?
YES: Repair the (C850) Blower Switch Position Signal circuit for a short to ground. Run the Cooldown Test again after the repair is complete.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 6
6. CHECK (C850) BLOWER SWITCH POSITION SIGNAL CIRCUIT FOR AN OPEN
Measure the resistance of the (C850) Blower Switch Position Signal circuit between the A/C Heater Control C1 harness connector and the A/C Heater Control C3 harness connector.
Q: Is the resistance below 5.0 ohms?
YES: Replace the A/C Heater Control. Run the Cooldown Test again after the repair is complete.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Repair the (C850) Blower Switch Position Signal circuit for an open. Run the Cooldown Test again after the repair is complete.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test