Circuit Description

PCM monitors inputs from various sensors to adjust fuel delivery and spark timing. When a high coolant temperature is detected, the PCM may enter a Hot Fuel Enrichment (HFE) mode. During HFE mode, a richer air/fuel ratio is commanded which can cause exhaust emissions to exceed Federal standards.

PCM calculates engine coolant temperature value based on IAT, engine speed, vehicle speed and engine load. PCM compares the calculated value to the actual ECT sensor signal input. If ECT sensor signal input is higher than calculated coolant temperature value, due to a skewed ECT or IAT sensor signal or an actual hot engine condition, DTC will set and PCM will disable HFE.

Conditions required to set DTC are:

• No MAF, MAP, ECT or VSS sensor DTCs set.
• Engine coolant temperature is 110°C or less at ignition on.
• Engine coolant temperature drops to less than 104°C anytime after ignition is turned on.
• IAT, engine load, engine speed and vehicle speed all within a specific range.
• PCM detects a higher engine coolant temperature than calculated coolant temperature.