Allison 3000 & 4000 Gen 4 Fault Code: P2184 Engine Coolant Temperature Sensor Circuit Low Input

DIAGNOSTIC RESPONSE:
Use default engine coolant values

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) receives an input from an Engine Coolant Temperature (ECT) sensor. The TCM supplies a 5V reference voltage signal into a voltage-sensing network that is connected to one side of the ECT sensor on W135. The other side of the ECT sensor is connected to the TCM analog ground on W158.

The resistance value of the ECT sensor determines the voltage drop in the ECT sensor circuit. As resistance changes, the voltage drop across the ECT sensor circuit also changes and varies the ECT sensor input voltage on W135. The TCM uses engine coolant temperature information to restrict retarder operation when an engine coolant overheat condition is detected.

CONDITIONS FOR RUNNING THE DTC:
1. After TCM initializes normally and engine speed is above 200 rpm for more than 5 seconds, this DTC test runs at 0.25 second intervals.
2. Retarder and ECT sensor autodetected or forced present by CMC (Override Retarder Autodetect//Override Engine Coolant Source).
3. This test is disabled for this ignition cycle when a failure is reported for this DTC or DTC P2185.
4. The retarder reduction and preselect, based on engine coolant temperature feature, is enabled in the calibration.

CONDITIONS FOR SETTING THE DTC:
The TCM detects engine coolant temperature greater than 149°C (300°F) for more than 10 seconds.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2184 is active, the following conditions occur:
1. The TCM does not illuminate the CHECK TRANS light.
2. DTC is stored in TCM history.
3. TCM uses default engine coolant temperature values.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC P2184 may be caused by:
1. Incorrect transmission fluid fill.
2. W135 shorted to ground, or shorted to another wire in chassis harness.
3. Broken or defective connector assemblies allowing pushed back pins to short together.
4. Unlocked connectors, missing seal plugs allowing moisture in connectors.
5. Defective ECT sensor.
6. Defective TCM.
7. High transmission fluid temperature.
8. Inadequate or obstructed vehicle cooling system.
9. Non-bypassed engine coolant thermostats that are not opening in time may cause overheat condition for transmission fluid temperature. Monitor transmission fluid temperature using the diagnostic tool and review transmission overheat and retarder information in General Troubleshooting of Performance Complaints.

The ECT sensor resistance is available on the diagnostic tool Data Monitor grid. Prior to ‘Connect’ for the diagnostic tool, check the ‘Troubleshoot Specific Problem’ box under “Connection Options” and then check the ‘Sensor, Voltage, Ohms, and Counts Data’ box.

Check if ECT sensor resistance is increasing, decreasing, or stationary with fluctuations in fluid temperature.

Refer to DTC P2740 and DTC P0218 or General Troubleshooting of Performance Complaints as guidelines for troubleshooting vehicle cooling issues.

Review applicable information in Control System and Transmission Specifications to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.