Pinpoint Test H: Insufficient, Erratic or No Heat
Climate Control System
Pinpoint Test H: Insufficient, Erratic or No Heat
Refer to Wiring Diagram Set 55 (Fusion/Milan/MKZ, Fusion Hybrid, Milan Hybrid, MKZ Hybrid), Automatic Climate Control System for schematic and connector information. Diagrams By Number
Normal Operation
Under normal operation, warm coolant flows from the engine through the auxiliary coolant flow pump to the heater core and back to the engine. The auxiliary coolant flow pump relay (switch side) is supplied voltage through circuit SBB13 (GY/RD). When the relay is energized by the PCM, the voltage is sent from the relay to the auxiliary coolant flow pump through circuit CHC01 (BN/YE). The auxiliary coolant flow pump is grounded through circuit GD112 (BK/YE). When the HVAC module is ON, a message is sent over the Controller Area Network (CAN) to the PCM. When the PCM receives the message, the PCM energizes the auxiliary coolant flow pump relay.
An auxiliary coolant flow pump is used only on hybrid vehicles to improve engine coolant circulation for heater operation at low engine speeds or when the engine is OFF.
The auxiliary coolant flow pump will be disabled when any of the following conditions are present:
- The climate control module is set to the OFF position.
- The ambient temperature is above 32°C (90°F).
- The coolant temperature is less than -10°C (14°F).
- The engine speed is above 4,000 rpm.
For a complete explanation of the auxiliary coolant flow pump, refer to heating and ventilation in the Description and Operation portion of Climate Control Description and Operation.
This pinpoint test is intended to diagnose the following:
- Plugged heater core
- Coolant level
- Temperature blend door
- Auxiliary coolant flow pump
- PCM
- HVAC module
PINPOINT TEST H: INSUFFICIENT, ERRATIC OR NO HEAT
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H1 CHECK FOR CORRECT ENGINE COOLANT LEVEL
- Ignition OFF.
- Check the engine coolant level when hot and cold.
- Is the engine coolant at the correct level (hot/cold) as indicated on the engine coolant recovery reservoir?
Yes
GO to H3.
No
GO to H2.
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H2 CHECK THE ENGINE COOLING SYSTEM FOR LEAKS
- Pressure test the cooling system for leaks. Refer to Engine Cooling Component Tests and General Diagnostics.
- Does the engine cooling system leak?
Yes
REPAIR the engine coolant leak. TEST the system for normal operation.
No
FILL and BLEED the cooling system. REFER to Engine Cooling Service and Repair. After filling and bleeding the cooling system, GO to H3.
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H3 CHECK FOR COOLANT FLOW TO THE HEATER CORE
- Start the engine and let the engine idle until it shuts down automatically,
- Select FLOOR mode.
- Set the temperature to the warmest setting.
- Select the lowest blower motor setting.
- Using a suitable temperature measuring device, check the heater core inlet hose to see if it is hot.
- Is the heater core inlet hose hot?
Yes
GO to H4.
No
GO to H5.
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H4 CHECK FOR A PLUGGED OR RESTRICTED HEATER CORE
- Using a suitable temperature measuring device, measure the heater core outlet hose temperature.
- Is the heater core outlet hose temperature similar to the inlet hose temperature (within approximately 6-17°C [10-30°F])?
Yes
REFER to Climate Control System - General Information and Diagnostics Climate Control System - General Information and Diagnostics and diagnose for temperature control is inoperative/does not operate correctly.
No
INSTALL a new heater core. TEST the system for normal operation.
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H5 CHECK FOR COOLANT FLOW TO THE AUXILIARY COOLANT FLOW PUMP
- Using a suitable temperature measuring device, check the auxiliary coolant flow pump inlet hose to see if it is hot.
- Is the auxiliary coolant flow pump inlet hose hot?
Yes
GO to H6.
No
REFER to Engine Cooling - Hybrid Testing and Inspection to check cooling system function.
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H6 CHECK CIRCUIT CHC01 (BN/YE) FOR VOLTAGE
- Ignition OFF.
- Disconnect: Auxiliary Coolant Flow Pump C1450.
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: DataLogger - PCM.
- Toggle the Heater Pump Commanded (HPUMP) output command ON.
- Measure the voltage between auxiliary coolant flow pump C1450-2, circuit CHC01 (BN/YE), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to H7.
No
CARRY OUT the auxiliary coolant flow pump relay component test.
If the relay tests OK, GO to H8.
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H7 CHECK CIRCUIT GD121 (BK/YE) FOR GROUND
- Ignition OFF.
- Measure the voltage between auxiliary coolant flow pump C1450-1, circuit GD121 (BK/YE), harness side and auxiliary coolant flow pump C1450-2, circuit CHC01 (BN/YE), harness side.
- Is the voltage greater than 10 volts?
Yes
INSTALL a new auxiliary coolant flow pump. REFER to Climate Control Service and Repair. TEST the system for normal operation.
No
REPAIR circuit GD121 (BK/YE) for an open. TEST the system for normal operation.
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H8 CHECK THE AUXILIARY COOLANT FLOW PUMP RELAY VOLTAGE SUPPLY
- Ignition OFF.
- Disconnect: Auxiliary Coolant Flow Pump Relay.
- Ignition ON.
- Measure the voltage between ground and auxiliary coolant flow pump relay socket, circuit SBB13 (GY/RD).
- Is the voltage greater than 10 volts?
Yes
REPAIR circuit CHC01 (BN/YE) for an open. TEST the system for normal operation.
No
VERIFY Battery Junction Box (BJB) fuse 13 (15A) is OK. If OK, REPAIR circuit SBB13 (GY/RD) for an open. TEST the system for normal operation. If not OK, Refer to the Wiring Diagrams to identify the possible causes of the circuit short. Diagrams By Number
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