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 ECM, it produces a 0 to 5 volt analog signal that indicates temperature. For the EOT sensor function diagram, see Figure
“Engine Oil Temperature Sensor Function Diagram”
.
Figure 1. Engine Oil Temperature Sensor Function Diagram
Cranking Fuel Quantity/Timing Control — The EOT signal is used to determine the timing and quantity of fuel required to optimize starting over all temperature conditions.
Temperature Compensation — Fuel quantity and timing is controlled throughout the total operating range to compensate for oil viscosity changes due to temperature variations and ensure that adequate torque and power is available.
Section 29.1.1
Fault Detection/Management
An EOT signal that is detected out of range high or low by the ECM will cause the ECM to ignore the EOT signal and default to the engine coolant temperature (ECT) sensor. The Warn Engine lamp will also be illuminated as long as the fault condition exists. If both the EOT and ECT sensors are not functioning, the ECM will assume a 212°F (100°C) value for engine oil temperature. For the EOT sensor, see Figure
“Engine Oil Temperature Sensor “
.
Figure 2. Engine Oil Temperature Sensor
Note: After removing connectors always check for damaged pins, corrosion, loose terminals, etc.
Connector voltage checks are listed in Table
“Connector Voltage Checks”
. These checks are performed with sensor connector disconnected and the ignition key ON.
| Test Points | Spec | Comments |
| B to Grd | 4.8 – 5.0v | Pull up voltage; if no or low voltage, circuit has open or high resistance or short to ground. |
| A to Grd | 0 – 0.25v | If greater than 0.25 volts, signal ground wire is shorted to VREF or battery. |
Connector checks to chassis ground are listed in Table
“Connector Checks to Chassis Ground”
. These checks are performed with the sensor connector disconnected, the ignition key OFF, and the positive battery cable disconnected.
| Test Points | Spec | Comments |
| A to Grd | < 5 Ω | Resistance to chassis ground, check with key OFF; if > 5 Ω, the harness is open. |
| B to Grd | > 1,000 Ω | Resistance less than 1,000 Ω indicates a short to ground. |
Harness resistance checks are listed in Table
“Harness Resistance Checks”
. These checks are performed with the breakout box installed on the engine harness only.
| Test Points | Spec | Comments |
| #19 to A | < 5 Ω | Resistance from sensor connector to 60-pin connector – Signal ground. |
| #12 to B | < 5 Ω | Resistance from sensor connector to 60-pin connector – EOT signal. |
Operational signal checks are listed in Table
“Operational Signal Checks”
. These checks are performed with the breakout box installed in line with the ECM.
| Test Points
(+) #12 to (-) #19 |
Operational Signal Checks
(Check with breakout box installed in line w/ECM) |
|||
| Voltage | Temp °F | Temp °C | Resistance | Comments |
| 0.53v | 248 | 120 | 1.19 K Ω | |
| 0.96v | 205 | 96 | 2 K Ω | |
| 1.45v | 176 | 80 | 3.84 K Ω | |
| 4.36v | 32 | 0 | 69.2 K Ω | |
| 4.64v | -5 | -20 | 131.0 K Ω | |
Fault code descriptions are listed in Table
“Fault Code Descriptions”
.
| Circuit Faults | Descriptions |
| 311 | Signal was less than 0.2 volts; more than 0.1 seconds. |
| 312 | Signal voltage was greater than 4.78 volts for more than 0.1 seconds. |
Section 29.1.2
Function
The engine control system includes an Engine Oil Temperature (EOT) sensor. The ECM monitors engine oil temperature via the EOT sensor signals to control fuel quantity and timing throughout the operating range of the engine. The EOT signal allows the ECM to compensate for oil viscosity variations due to temperature changes in the operating environment. This ensures that adequate power and torque are available under all operating conditions.
Section 29.1.3
Operation
The EOT sensor is a thermistor type sensor that changes resistance when exposed to different oil temperatures.
When the temperature of the oil is decreased, the resistance of the thermistor increases, which causes the signal voltage to increase. As the temperature of the oil is increased, the resistance of the thermistor decreases, causing the signal voltage to decrease.
The EOT sensor is supplied a regulated 5 volt reference signal at terminal B from the ECM. A return circuit (ground) is supplied at terminal A from the ECM. As the oil temperature increases or decreases, the sensor changes resistance and provides the ECM with the oil temperature signal voltage. This signal voltage is then read by the ECM to determine the temperature of the oil.
Section 29.1.4
ECM Diagnostics
With the ignition key ON, the ECM continuously monitors the EOT signal to determine if it is within expected values. If the signal voltage is above or below the expected levels, the ECM will set a fault code.
If the ECM detects a fault, it will use the value of the Engine Coolant Temperature signal, in place of the EOT signal. If the ECT sensor is not sending a correct signal, the ECM will default to 29°F (-1.7°C) for starting or 212°F (100°C) for engine running operation.
EOT sensor faults can be retrieved using the EST or by reading the flash codes from the warning light using the STI diagnostic switch located on the vehicle dash. If the ignition key is shut off, the code will become an inactive code. EOT codes will cause the Engine Warning light to be illuminated.
Section 29.1.5
Flash Codes
The following flash codes could display when troubleshooting the EOT.
Section 29.1.5.1
Flash Code 311
ATA Code PID 175 FMI 4
Engine Oil Temperature signal out of range LOW.
Flash Code 311 out of range low will be set if the signal voltage was less than 0.2 volts for longer than 0.1 seconds. If this code is set, the ECM will default to ECT temperature or a default value of −4°F (−20°C) for starting or 212°F (100°C) for engine running operation. This code will cause the ECM to illuminate the engine warning light.
Flash Code 311 may be set due to a short to ground in the signal circuit or a defective sensor.
Section 29.1.5.2
Flash Code 312
ATA Code PID 175 FMI 3
Engine Oil Temperature signal out of range HIGH.
Flash Code 312 out of range high will be set if the signal voltage is more than 4.8 volts for more than 0.1 seconds. If this code is set, the ECM will default to ECT temperature or a default value of −4°F (−20°C) for starting or 212°F (100°C) for engine running operation. This code will cause the ECM to illuminate the engine warning light.
Flash Code 312 may be set due to an open signal circuit between the ECM and the sensor or a short to a voltage source. A defective sensor may also cause Flash Code 312 to be set.
| Series 40E Troubleshooting Manual – 6SE241 |
| Generated on 10-13-2008 |