Engine Cooling System Outputs

The engine cooling system may contain multiple control valves for improving fluid warm-up rates of both the engine and transmission. These valves are PCM controlled and primarily used for thermal control of engine metal and transmission fluid temperatures by diverting engine coolant to the appropriate component. These digital outputs include an engine coolant bypass valve, a heater core shut-off valve, an active transmission heating valve, and an active transmission cooling valve.

Courtesy of

The Engine Coolant Bypass Valve is normally closed (de-energized) forcing all of the engine coolant through the radiator to provide maximum "cooling" of the engine and components when the thermostat is open. When opened, a portion of the engine coolant bypasses the radiator providing for coolant pressure and flow control. The Heater Core Shut Off valve has a single purpose which is to limit coolant flow for fast engine warm-up. The active transmission cooling valve will transfer engine coolant from the sub-radiator to the transmission oil cooler when energized, resulting in a heat transfer from the transmission into the engine coolant (over-temperature control of the transmission). The active transmission heating valve is used to provide hot engine coolant to the TOC to improve transmission fluid temperature control.

The Engine Coolant Radiator Bypass Valve output circuit is checked for opens and shorts (P26B7).

COOLANT BYPASS VALVE SOLENOID CHECK OPERATION

DTCs	P26B7 - Engine Coolant Bypass Valve "C" Control Circuit where "C" is defined as "Engine Coolant Radiator"
Monitor Execution	Continuous
Monitor Sequence	None
Sensors OK	Not Applicable
Monitoring Duration	5 seconds

TYPICAL ENGINE COOLANT BYPASS VALVE CHECK MALFUNCTION THRESHOLDS

P26B7 - Smart driver reports output circuit fault

The Engine Coolant Cabin Heating (Heater Core) Bypass Valve output circuit is checked for opens and shorts (P26BD).

ENGINE COOLANT CABIN HEATING BYPASS VALVE CHECK OPERATION

DTCs	P26BD - Engine Coolant Bypass Valve "D" Control Circuit where "D" is defined as "Engine Coolant Cabin Heating"
Monitor Execution	Continuous
Monitor Sequence	None
Sensors OK	Not Applicable
Monitoring Duration	5 seconds

TYPICAL ENGINE COOLANT CABIN HEATING BYPASS VALVE CHECK MALFUNCTION THRESHOLDS

P26BD - Smart driver reports output circuit fault.

The Active Transmission Heating Valve output circuit is checked for opens and shorts (P2681).

ACTIVE TRANSMISSION HEATING VALVE SOLENOID CHECK OPERATION

DTCs	P2681 - Engine Coolant Bypass Valve "A" Control Circuit where "A" is defined as "Engine Coolant Auto Trans Cooler Flow"
Monitor Execution	Continuous
Monitor Sequence	None
Sensors OK	Not Applicable
Monitoring Duration	5 seconds

TYPICAL ACTIVE TRANSMISSION HEATING VALVE SOLENOID CHECK MALFUNCTION THRESHOLDS

P26B7 (Active Transmission Heating Valve Solenoid Circuit): open/shorted

The Active Transmission Cooling Valve output circuit is checked for opens and shorts (P26AC).

ACTIVE TRANSMISSION COOLING VALVE SOLENOID CHECK OPERATION

DTCs	P26AC - Engine Coolant Bypass Valve "B" Control Circuit Where "B" is defined as "Engine Coolant Auto Trans Cooling"
Monitor Execution	Continuous
Monitor Sequence	None
Sensors OK	Not Applicable
Monitoring Duration	5 seconds

TYPICAL ACTIVE TRANSMISSION COOLING VALVE SOLENOID CHECK MALFUNCTION THRESHOLDS

P26AC - Smart driver reports output circuit fault.