The Engine Coolant Temperature (ECT) 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. See Figure
“Engine Coolant Sensor Function Diagram”
.
Figure 1. Engine Coolant Sensor Function Diagram
Coolant Temperature Compensation — At coolant temperatures greater than 214°F (101°C) full load fuel quantity is reduced by approximately 6% for each degree of temperature, until the engine temperature reaches 218°F (103°C). Above 218°F (103°C), fuel is reduced by 3% for each °C increase in temperature.
Idle Speed — At temperatures below 158°F (70°C), low idle is incrementally increased to a maximum of 875 r/min.
Engine Warning and Protection — Optional feature when enabled will warn driver of overheat condition and can be programmed to shut the engine down.
Section 26.1.1
Fault Detection/Management
An ECT signal that is detected out of range high or low by the ECM will cause the ECM to ignore the ECT signal and assume an engine coolant temperature of −29°F (−20°C), for starting and a temperature of 180°F (82°C) for engine running conditions. The warning lamp will also be illuminated as long as the fault condition exists. See Figure
“Connector Voltage Checks”
.
Figure 2. Connector Voltage Checks
Note: After removing connectors, always check for damaged pins, corrosion, loose terminals, etc.
Connector voltage checks are made with the sensor connector disconnected and the ignition key ON. Checks are listed in Table
“Connector Voltage Checks”
.
| Test Points | Spec. | Comments |
| B to Grd | 4.6 – 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, wire is shorted to VREF or battery. |
Connector checks to chassis ground are made with the sensor connector disconnected, the positive battery cable disconnected, and the ignition key OFF. Checks are listed in Table
“Connector Checks to Chassis Ground”
.
| Test Points | Spec. | Comments |
| A to Grd | < 5 Ω | Resistance to chassis ground, check with key off, > 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 made with the breakout box installed on the engine harness only. Checks are listed in Table
“Harness Resistance Checks”
.
| Test Points | Spec. | Comments |
| #19 to A | < 5 Ω | Resistance from harness connector to 60-pin connector – Signal ground. |
| #13 to B | < 5 Ω | Resistance from harness connector to 60-pin connector – ECT signal. |
Operational signal checks are made with the breakout box installed on the ECM and engine (Gray) harness. Checks are listed in Table
“Operational Signal Checks”
.
| Test Points
(+) #13 to (−) #19 |
Operational Signal Checks | |||
| Voltage | Temp °F | Temp °C | Resistance | Comments |
| 0.356v | 230 | 110 | 1.19 K Ω | |
| 0.552v | 209 | 99 | 2 K Ω | |
| .648 | 199 | 93 | 3.84 K Ω | |
| 3.87v | 32 | 0 | 69.2 K Ω | |
| 4.33v | −5 | −20 | 131 K Ω | |
Fault code descriptions are listed in Table
“Fault Code Descriptions”
.
| Circuit Faults | |
| 114 | Signal was less than 0.127 volts for more than 0.1 seconds. (Probable short to ground.) |
| 115 | Signal voltage was greater than 4.6 volts for more than 0.1 seconds. (Probable open circuit.) |
| Cooling System Faults | |
| 316 | Engine temp has not warmed above spec after 120 minutes of operation. (Only on engines with cold ambient protection turned on.) |
| 321 | Engine Coolant Temperature above WARN level 228°F (109°C). |
| 322 | Engine Coolant Temperature above Critical level 234°F (112.5°C). |
| 325 | Coolant Temperature Compensation enabled. (Reduces fuel quantity 6% for each °C above 225°F (107°C). |
Section 26.1.2
Function of Extended System
The DDC engine control system includes an Engine Coolant Temperature sensor. The ECM measures the engine coolant temperature signal and uses this information for coolant temperature compensation and optional high temperature warning and shut down systems.
Coolant Temperature Compensation protects the engine if the coolant temperature is too high. The ECM monitors the ECT signal to determine the coolant temperature. If the coolant reaches 214°F (101°C), the ECM will reduce the fuel delivery by 6% for each Celsius degree of temperature increase. If the coolant temperature increases to 218°F (104°C), fuel quantity will be reduced 3% for each Celsius degree of temperature increase. Coolant temperature compensation can be programmed to be inoperative in certain applications where full engine performance is required over the protection of the engine.
On engines equipped with an engine warning system, the ECM will activate the audible warning alarm and illuminate the red Oil/Water warning light when the engine coolant temperature reaches 225°F (107°C).
On engines equipped with an engine shutdown system, the ECM will shut the engine off when the coolant temperature reaches 235°F (112.5°C). The vehicle operator may restart the engine by turning the ignition key OFF and then restarting it. Upon restart, the ECM will allow the engine to run for an additional 30 seconds before shutting off the engine again.
Section 26.1.3
Operation
The ECT sensor is a thermistor type sensor that changes resistance when exposed to different temperatures.
When the temperature of the coolant is decreased, the resistance of the thermistor increases which causes the signal voltage to increase. As the temperature of the coolant is increased, the resistance of the thermistor decreases, which causes the signal voltage to decrease.
The ECT sensor is supplied a regulated 5 volt reference voltage from the ECM. The sensor is grounded at terminal A through the signal return terminal at the ECM. As the coolant temperature increases or decreases, the sensor changes resistance and provides the ECM with the coolant temperature signal voltage at the ECM. This signal voltage is then read by the ECM to determine the temperature of the coolant.
Section 26.1.4
ECM Diagnostics
With the ignition key ON, the ECM continuously monitors the ECT circuit for expected voltages. If the signal voltage is less than or more than expected, the ECM will set a fault code.
If the ECM detects a fault in the ECT signal, the ECM will disregard the signal and default to a temperature of 180°F (82°C) for engine running operation and −29°F (−33.9°C) for starting the engine. If the fault is no longer present, the ECM will once again return to normal operation using the ECT signal for processing.
Faults in the ECT signal can be retrieved using the Self Test Input Switch (STI) or the Electronic Service Tool (EST). If the fault is no longer present, it will be stored as an inactive code.
Section 26.1.5
Flash Codes
The following flash codes could result from ECT sensor problems:
Section 26.1.5.1
Flash Code 114
ATA Code PID 110 FMI 4
Out of Range LOW
An out of range low code will be set if the ECM detects a voltage less than .127 volts for more than 0.1 seconds. If this fault is active, the ECM will use the default value of 180°F (82°C).
Flash Code 114 may be caused by a short to ground or a shorted or biased sensor.
Section 26.1.5.2
Flash Code 115
ATA Code PID 110 FMI 3
ECT: Out of range HIGH
An out of range high code will be set if the ECM detects a voltage greater than 4.6 volts for more than 0.1 seconds. If this fault is active, the ECM will use the default value of 180°F (82°C).
Flash Code 115 may be caused by an open circuit, an open sensor, or a short to another voltage source.
Section 26.1.5.3
Flash Code 321
ATA Code PID 110 FMI 0
Engine coolant temperature above warning level.
Flash Code 321 will be set if the ECM detects engine coolant temperature above 225°F (107°C). When this occurs, the ECM illuminates the OIL/WATER warning light and sounds the audible alarm (if equipped), alerting the operator that a potential for engine damage exists.
If the temperature drops below 225°F (107°C), the code will become inactive and the ECM will return to normal operation.
Section 26.1.5.4
Flash Code 322
ATA Code PID 110 FMI 7
Engine coolant temperature above critical level.
Flash Code 322 will be set if the ECM detects engine coolant temperature above 235°F (112.5°C). When this occurs, the OIL/WATER warning light illuminates and the audible alarm sounds (if equipped) alerting the operator that the temperature is increasing (having set code 321) indicating a potential for engine damage. With code 322 active, the engine will shut down. At the same time a fault code, current engine hours and odometer reading, will be recorded in the ECM as an Engine Event.
If the temperature drops below 235°F (112.5°C), the code will become inactive and the ECM will return to normal operation. Should the engine shut down, it can be restarted to move the vehicle to a safe place.
Section 26.1.5.5
Flash Code 325
ATA Code PID 110 FMI 14
Power reduced, matched to cooling system performance.
Flash Code 325 will be set if the cooling system temperature exceeds 214°F (101°C). At this temperature the ECM will reduce the fuel delivered to the engine. For each one Celsius degree of temperature, the fuel will be reduced 6%. This reduces the heat produced by the engine, thereby reducing the burden on the engine cooling system. It will also slow the vehicle speed encouraging the operator to downshift, thus increasing the efficiency of the cooling system.
As the temperature is reduced, the compensation level is reduced, until the temperature drops below 214°F (101°C), at which normal operation is resumed.
Section 26.1.5.6
Flash Code 316
ATA Code PID 110 FMI 1
CAP fault code — unable to warm engine.
Flash Code 316 will only be set with engines that have CAP (Cold Ambient Protection) strategy enabled. This code is set after the engine has run for greater than 120 minutes and has not exceeded the following specifications for engine coolant temperature. This code can be cleared with the EST.
- DT 466E / 530E
- Manual Transmission 142°F / 61°C
- Automatic Transmission 106°F / 41°CNote: This code only indicates that the engine has not been able to reach operating temperature. It does not indicate an electronic fault.
Possible System Faults include:
- Extended idle time
- Cold ambient temperatures (may require use of winter front)
- Thermostat stuck in open position
- Mis-plumbed cooling system (thermostat bypassed)
- Auxiliary heater cores cooling off engine (school bus application)
- Fan clutch locked on
Recommended actions are listed in Table
“System Faults”
.
| Condition | Action |
| Extended idle time. | Recommend to reduce idle time or increase idle speed. |
| Cold ambient temperatures (may require use of winter front). | Recommend use of winter front. |
| Thermostat stuck in open position. | Perform thermostat tests per service manual. |
| Mis-plumbed cooling system. | Verify correct cooling system routing. |
| Auxiliary heater cores cooling off engine. | Reduce flow to heater cores or slow down fan speed of heater. |
| Fan clutch locked on. | Verify proper fan clutch operation. |
| Series 40E Troubleshooting Manual – 6SE241 |
| Generated on 10-13-2008 |