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 (CBV), a heater core shut-off valve (HCSO), an active transmission heating valve (ATWU-H), and an active transmission cooling valve (ATWU-C).

Courtesy of

The 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 ATWU-C valve will transfer engine coolant from the sub-radiator to the Transmission Oil Cooler (TOC) when energized, resulting in a heat transfer from the transmission into the engine coolant (over-temperature control of the transmission). The ATWU-H valve is used to provide hot engine coolant to the TOC to improve transmission fluid temperature control.

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

The Heater Core Shut-Off Valve output circuit is checked for opens and shorts (P26BD).

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

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