2021 Freightliner M2 Low Coolant Level Troubleshooting

Introduction

This document outlines common issues and troubleshooting steps for low coolant level (LCL) faults reported on 2021 Freightliner M2 trucks, particularly those equipped with Cummins engines. The problem typically involves the coolant level sensor and its associated components.

Common Symptoms and Initial Observations

Vehicles may display a low coolant level warning or fault code. Initial reports suggest that even when the coolant tank appears full, the system may still indicate a low level. This often points to an issue with the float mechanism within the coolant reservoir or the sensor itself.

Some users note that Cummins troubleshooting procedures may not always align with Freightliner components, requiring specific attention to the vehicle's integrated systems.

Troubleshooting the Coolant Level Sensor and Float

The coolant level sensor typically operates based on the position of a float within the coolant reservoir. The resistance of the sensor changes depending on whether the float is up (indicating sufficient coolant) or down (indicating low coolant).

Resistance Values:
- Full Coolant: Approximately 50-133 ohms.
- Low Coolant: Approximately 150-1200 ohms.
- Short Circuit Fault: Readings below 133 ohms.
- Open Circuit Fault: Readings above 1200 ohms.
Testing the Float:
- Gently tap the coolant tank to dislodge a potentially stuck float.
- If the float is suspected to be stuck, slowly remove the sensor probe while monitoring diagnostic data (DL). If the system registers 'full' as the probe is removed, the float was likely stuck low.
Testing the Sensor and Wiring:
- Disconnect the sensor and measure its resistance.
- Perform a "pull test" on the wires at the connector to check for broken copper or stretched insulation.
- Check for corrosion at the sensor and firewall connectors.
- Measure resistance to ground on the LCL circuits while wiggling the harness to detect intermittent faults.
- Gently flex the sensor while measuring resistance to check for internal issues.

The Coolant Level Module (Medallion Module)

In addition to the sensor, a "Low Coolant Module" or "Medallion module" is often present. This module typically converts a 5-volt signal from the ECM into an AC voltage that interacts with the coolant. Changes in this voltage indicate the coolant level.

It is common for this module to fail, sometimes taking the sensor with it. Many technicians recommend replacing both the sensor and the module when troubleshooting LCL faults, as they can be interdependent.

This module may have started appearing on builds from 2020 onwards. For more information on chassis routing, refer to: Freightliner Technical Support.

Wiring Diagram and Electrical Considerations

Schematics show the coolant level float sensor connecting to the Engine Control Module (ECM) via various modules, including the Frontwall and Engine Dash. Key connections include the 5V supply, ground, and the sensor signal wires.

The diagram illustrates the relationship between sensor resistance and coolant level, with calculations showing how voltage and current relate to resistance values (e.g., 5V + 1200 ohms ≈ 0.042A; 5V + 133 ohms ≈ 0.038A).

Important Note: Ensure all connections between the 5V supply and ground are secure and free of added resistance. Visually inspect wiring for chafing or damage.

Part Numbers and Common Fixes

The correct part number for the coolant level sensor is frequently cited as 06-93316-002. There have been instances where incorrect part numbers were specified in Bill of Materials (BOMs).

Commonly reported fixes include:

Replacing the coolant level sensor (Part No. 06-93316-002).
Replacing the Low Coolant Module.
Replacing both the sensor and the module.
Addressing wiring issues such as corrosion or breaks.
Resolving issues with a stuck float in the coolant tank.

When troubleshooting, it is advisable to consider both the sensor and the module as potential failure points.

Diagnostic Fault Codes

Common fault codes associated with this issue include:

197: Coolant Level - Data Valid But Below Normal Operating Range - Moderately Severe Level
3366: Coolant Level - Data Valid But Below Normal Operating Range - Moderately Severe Level
195: Coolant Level Sensor 1 Circuit - Voltage Above Normal or Shorted to High Source
196: Coolant Level Sensor 1 Circuit - Voltage Below Normal or Shorted to Low Source

Clearing faults may require specific conditions, such as idling the engine for a minute after repairs.

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