Fail-Safe Cooling Strategy

Fail-safe cooling strategy is activated by PCM only in the event that an overheating condition has been detected. This strategy provides engine temperature control when cylinder head temperature exceeds certain limits. Cylinder head temperature is measured by Cylinder Head Temperature (CHT) sensor. For additional CHT sensor information, see CYLINDER HEAD TEMPERATURE SENSOR under INPUT DEVICES.

NOTE: Not all vehicles equipped with a CHT sensor will have fail-safe cooling strategy.

A cooling system failure such as low coolant or coolant loss could cause an overheating condition. As a result, damage to major engine components could occur. Along with a CHT sensor, fail-safe cooling strategy is used to prevent damage by allowing air cooling of engine. This strategy allows the vehicle to be driven safely for a short time with some loss of performance when an overheating condition exists. Engine temperature is controlled by varying and alternating the number of disabled fuel injectors. This allows all cylinders to cool. When fuel injectors are disabled, their respective cylinders work as air pumps, and this air is used to cool the cylinders. The more fuel injectors that are disabled, the cooler the engine runs, but the engine has less power.

NOTE: A Wide Open Throttle (WOT) delay is incorporated if CHT temperature is exceeded during WOT operation. At WOT, injectors will function for a limited amount of time allowing customer to complete a passing maneuver.

Before injectors are disabled, fail-safe cooling strategy alerts customer to a cooling system problem by moving instrument cluster temperature gauge to HOT zone and a PCM DTC P1285 is set. Depending on the vehicle, other indicators, such as an audible chime or warning lamp, can be used to alert customer of fail-safe cooling. If overheating continues, fail-safe cooling strategy begins to disable fuel injectors, a DTC P1299 is stored in PCM memory and a Malfunction Indicator Light (MIL), either CHECK ENGINE or SERVICE ENGINE SOON will illuminate. If overheating condition continues and a critical temperature is reached, all fuel injectors are turned off and engine is disabled.