Fault Code 370: Countershaft Speed
J1939: SA 3 SPN 160 FMI 2, 3, 4, 5, 6, 8, 9, 10, 14, 20, 21
Overview
The Endurant HD transmission is equipped with speed sensors to monitor input, countershaft and output speeds. The speed sensors provide rotational speed inputs to the Transmission Control Module (TCM) to verify clutch operation and calculate gear ratios. The Countershaft Speed Sensor measures the rotational speed of the countershafts. The Input Shaft and Countershaft Speed Sensors are mounted internally and attached to the Mechatronic Transmission Module (MTM) and connected to the TCM at the 74-Way Transmission Harness Connector.
Detection
The TCM monitors the Countershaft Speed signal. If a system failure is detected, the fault is set Active.
Conditions to Set Fault Code Active
FMI 2 – Data Erratic: Countershaft Speed Sensor out of range for 5 seconds.
FMI 3 - Voltage Above Normal or Shorted High: Countershaft Speed Sensor circuit shorted to power for 5 seconds.
FMI 4 – Voltage Below Normal or Shorted Low: Countershaft Speed Sensor circuit shorted to ground for 5 seconds.
FMI 5 – Current Below Normal or Open Circuit: Countershaft Speed Sensor circuit open or shorted to power for 5 seconds.
FMI 6 - Current Above Normal or Grounded Circuit: Countershaft Speed Sensor out of normal operating voltage (4.75V to 5.25V) for 5 seconds.
FMI 8 – Abnormal Frequency: Countershaft Speed Sensor out of normal operating frequency for 5 seconds.
FMI 9 – Abnormal Update Rate: Countershaft Speed Sensor direction unknown for 5 seconds.
FMI 10 - Abnormal Rate of Change: Countershaft Speed Sensor rate of change exceeded for 2 seconds.
FMI 14 – Special Instructions: Countershaft Speed out of range (near 0 RPM) when compared to calculated countershaft speeds based on known Input speed, Output speed and gear ratio, for 5 seconds.
FMI 20 – Data Drifted High: Countershaft Speed greater than expected when compared to calculated countershaft speeds based on known Input speed, Output speed and gear ratio, for 2 seconds.
FMI 21 – Data Drifted Low: Countershaft Speed less than expected when compared to calculated countershaft speeds based on known Input speed, Output speed and gear ratio, for 2 seconds.
Fallback
FMI 2, 3, 4, 5, 6, 8, 9, 10, 14, 20, 21
- Amber warning lamp on
- Inertia Brake activation prohibited
- If Fault Codes 350 and 375 are both Active and vehicle is moving:
- Red stop lamp on
- Urge to Move and Creep Mode prohibited
- Inertia Brake activation prohibited
- Non-Neutral modes prohibited
- PTO Mode prohibited
Conditions to Set Fault Code Inactive
FMI 2, 3, 4, 5, 6, 8, 9, 10: Countershaft Speed Sensor in range for 10 seconds.
FMI 14, 20, 21: Countershaft Speed signal matches calculated countershaft speeds for 10 seconds.
Possible Causes
FMI 2, 14, 20, 21:
- MTM - Countershaft Speed Sensor
- Internal failure
- Damaged
- Internal Transmission
- Mechanical failure
- TCM
- Software issue
- Internal failure
FMI 3:
- TCM
- Software issue
- Internal failure
FMI 4, 5, 6, 8, 9, 10:
- MTM - Countershaft Speed Sensor
- Internal failure
- Damaged
- MTM - Countershaft Speed Sensor Harness
- Wiring shorted to power, shorted to ground or open
- MTM - Transmission Harness
- Wiring shorted to power, shorted to ground or open
- TCM
- Software issue
- Internal failure
Additional Tools
- Endurant HD Service Manual TRSM0950
- Eaton Breakout Box with 74-Way Eaton Diagnostic Adapter - RR1029TR
- Digital Volt/Ohm Meter (DVOM)
Component Identification
 |
1. Transmission Control Module (TCM) Cover 2. Transmission Control Module (TCM) 3. 74-Way Transmission Harness Connector (MTM-side) 4. 74-Way Transmission Harness Connector (TCM-side) 5. Transmission Control Module (TCM) Seal 6. Mechatronic Transmission Module (MTM) |
Fault Code 370 Troubleshooting
Set vehicle parking brake and chock wheels.
Record the transmission fault codes, FMIs, occurrences, and timestamps from the Service Activity report created during the Diagnostic Procedure.
If Fault Code 370 FMI 3 is Active or Inactive, Go to Step H
If Fault Code 370 FMI 4, 5, 6, 8, 9, 10 is Active or Inactive, Go to Step B
If Fault Code 370 FMI 2, 14, 20, 21 is Active or Inactive, Go to Step D
Key off.
Remove the TCM from the MTM with the 20-Way TCM Vehicle Harness Connector and 20-Way TCM Body Harness Connector connected.
Inspect the TCM side of the 74-Way Transmission Harness Connector, verify the connector is free from contamination and corrosion; the terminals are not bent, spread or loose; and there is no damage to the connector body.
Inspect the TCM Seal, verify the seal is properly installed and not damaged.
If contamination or damage is found to the TCM side of the 74-Way Transmission Harness Connector, replace the Transmission Control Module (TCM) and Mechatronic Transmission Module (MTM). Go to Step V
Note: MTM removal and installation requires the transmission to be removed from the vehicle. Reference Endurant HD Service Manual TRSM0950, Transmission Removal Service Procedure.
If no contamination or damage is found, Go to Step C
Key off.
Connect the Eaton Breakout Box with 74-Way Eaton Diagnostic Adapter to the TCM side of the 74-Way Transmission Harness Connector.
Key on.
Measure voltage at the Eaton Breakout Box between Pin 32 and Pin 42. Record reading in table.
Compare reading(s) in table.
If readings are in range, replace the Mechatronic Transmission Module (MTM). Go to Step V
Note: MTM removal and installation requires the transmission to be removed from the vehicle. Reference Endurant HD Service Manual TRSM0950, Transmission Removal Service Procedure.
If readings are out of range, replace Transmission Control Module (TCM). Go to Step V
| Ignition State | Pins | Range | Reading(s) |
|---|---|---|---|
| Key on | 32 to 42 | 4.75–5.25 V |
Key off.
Remove the TCM from the MTM with the 20-Way TCM Vehicle Harness Connector and 20-Way TCM Body Harness Connector connected.
Inspect the TCM side of the 74-Way Transmission Harness Connector, verify the connector is free from contamination and corrosion; the terminals are not bent, spread or loose; and there is no damage to the connector body.
Inspect the TCM Seal, verify the seal is properly installed and not damaged.
If contamination or damage is found to the TCM side of the 74-Way Transmission Harness Connector, replace the Transmission Control Module (TCM) and Mechatronic Transmission Module (MTM). Go to Step V
Note: MTM removal and installation requires the transmission to be removed from the vehicle. Reference Endurant HD Service Manual TRSM0950, Transmission Removal Service Procedure.
If no contamination or damage is found, Go to Step E
Key off.
Connect the Eaton Breakout Box with 74-Way Eaton Diagnostic Adapter to the TCM side of the 74-Way Transmission Harness Connector.
Key on.
Measure voltage at the Eaton Breakout Box between Pin 32 and Pin 42. Record reading in table.
Compare reading(s) in table.
If readings are in range, Go to Step F
If readings are out of range, replace Transmission Control Module (TCM). Go to Step V
| Ignition State | Pins | Range | Reading(s) |
|---|---|---|---|
| Key on | 32 to 42 | 4.75–5.25 V |
Key off.
Remove the MTM.
Note: MTM removal and installation requires the transmission to be removed from the vehicle. Reference Endurant HD Service Manual TRSM0950, Transmission Removal Service Procedure.
Inspect the lower countershaft Primary Drive Gear for missing teeth and excessive movement.
If no missing teeth or no excessive movement evident, replace the Mechatronic Transmission Module (MTM). Go to Step V
If missing teeth and/or excessive movement evident, identify cause of missing teeth and/or excessive movement and repair. Go to Step G
Inspect the Countershaft Speed Sensor in the MTM for damage.
If no Countershaft Speed Sensor damage is evident, Go to Step V
If Countershaft Speed Sensor damage is evident, replace the Mechatronic Transmission Module (MTM). Go to Step V
Confirm a Service Activity Report was downloaded and sent to Eaton.
Retrieve and record the transmission fault codes and FMI’s, and their occurrences and timestamps.
If Fault Code 370 FMI 3 is Active or Inactive, replace Transmission Control Module (TCM). Go to Step V
Key off.
Reconnect all connectors and verify that all components are properly installed.
Key on with engine off.
Connect ServiceRanger.
Go to “Fault Codes”.
Select “Clear All Faults”.
Operate vehicle and attempt to reset the fault code or duplicate the previous complaint.
Check for fault codes using ServiceRanger.
If no fault codes set and the vehicle operates properly, test complete.
If Fault Code 370 sets Active during operation, contact Eaton Cummins Automated Transmission Technologies at 800-826-4357 for further diagnostic instructions.
If a fault code other than 370 sets Active, go to Fault Code Isolation Procedure Index.