Systems and methods for diagnosing stuck ATWU valve

A system for a vehicle, comprising:

• a coolant system configured to circulate coolant through at least an engine, a radiator, a heater core;
• a controller, storing instructions in non-transitory memory that, when executed, cause the controller to:
• during a cold start of the engine, perform a monitoring routine that monitors a status of an Active Transmission Warmup (ATWU) valve of the coolant system that when commanded open, allows the coolant to circulate through a transmission heat exchanger of the vehicle, the monitoring routine comprising:
• determining a temperature difference between an engine coolant temperature (ECT) and a transmission fluid temperature (TFT) over a duration before the ATWU valve is commanded from an open position to a closed position or from the closed position to the open position;
• comparing a rate of change of the TFT before and after the ATWU valve is commanded from the open position to the closed position or from the closed position to the open position;
• indicating a stuck ATWU valve based on at least one of the temperature difference, the TFT rate of change comparison, or a combination thereof, based on a calibration parameter;
• and
• limit an acceleration of the vehicle in response to the stuck ATWU valve being indicated.

A method for a controller of a vehicle including an Active Transmission Warmup (ATWU) valve, the method comprising:

• based on a calibration parameter being equal to a first value, determining whether the ATWU valve is stuck based on calculating an area integral between a first curve defined by an engine coolant temperature (ECT) and a second curve defined by a transmission fluid temperature (TFT) over a duration before the ATWU valve is commanded open;
• based on the calibration parameter being equal to a second value, determining whether the ATWU valve is stuck based on calculating a first slope of a first curve defined by TFT measurements taken prior to commanding the ATWU valve open, calculating a second slope of a second curve defined by TFT measurements taken after commanding the ATWU valve open, and comparing the first slope to the second slope;
• based on the calibration parameter being equal to a third value, determining whether the ATWU valve is stuck based on both calculating the area integral and comparing the first slope to the second slope;
• in response to at least one of the area integral being less than a first threshold value and a difference between the second slope and the first slope being less than a second threshold value, setting a diagnostic flag;
• and
• in response to the diagnostic flag being set, indicating that the ATWU valve is stuck.