Diagnostic Aids

The Engine Oil Temperature (EOT) sensor is a thermistor type sensor that has a variable resistance that changes when exposed to different temperatures. When interfaced with the Powertrain Control Module (PCM), it produces a 0 to 5 volt analog signal that will deduce temperature.

1. Cranking Fuel Quantity/Timing Control
   
   The EOT sensor signal is used to determine the timing and quantity of fuel required to optimize starting over all temperature conditions.
2. Idle Speed
   
   At oil temperatures below 158°F (70°C) low idle is incrementally increased to a maximum of 950 RPM.
3. Temperature Compensation
   
   Fuel quantity and timing is controlled throughout the total operating range to ensure adequate torque and power is available.
4. Glow Plug Control
   
   The Glow Plug Control Module (GPCM) and lamp ON times are controlled by engine oil temperature.

An EOT sensor signal that is detected out of range (high or low) by PCM will cause PCM to ignore EOT sensor signal and assume an engine oil temperature of -4°F (-20°C) for starting, and a temperature of 212°F (100°C) for engine-running conditions. The Malfunction Indicator Light (MIL) will also be illuminated as long as condition exists. This test is intended to diagnose the following components and circuits:

• Engine Oil Temperature (EOT) Sensor
• Wiring Harness Circuits; (EOT & SIG RTN)
• Powertrain Control Module (PCM)

Fig 1: Identifying EOT Sensor Connector Terminals

Courtesy of FORD MOTOR CO.