Endurant HD
TRTS0950 EN-US
|
October 2024 - B

Fault Code 120: Start Enable Relay

J1939: SA 3 SPN 1321 FMI 3, 4, 5, 7, 12

Overview

The Endurant HD transmission disables engine cranking when the transmission is in a non-neutral gear position. Some vehicles prevent non-neutral engine cranking through the use of a normally open Start Enable Relay (SER) actuated by the Transmission Control Module (TCM) to interrupt power to the starter. Other vehicles rely on the TCM to send a Transmission Engine Crank Enable message over the Primary Data Link before the engine ECU will allow cranking. The SER and control circuits are contained within the 20-Way TCM Vehicle Harness Connector. Consult OEM wiring diagrams.

This fault indicates an electrical failure was detected in the SER or control circuits when the start enable type is configured for a relay in the TCM. This fault code will not set on vehicles that use J1939 messaging to enable engine cranking.

Detection

The TCM monitors the SER control circuits. If a system failure is detected, the fault is set active.

Conditions to Set Fault Code Active

FMI 3 – Voltage Above Normal or Shorted High: SER circuit shorted to power for 1 second.

FMI 4 – Voltage Below Normal or Shorted Low: SER circuit shorted to ground for 1 second.

FMI 5 – Current Below Normal or Open Circuit: SER circuit open for 1 second.

FMI 7 – Mechanical System Not Responding: Engine cranked when SER was not energized by the TCM for 2 seconds.

FMI 12 – Bad Intelligent Device: SER enabled under inappropriate conditions.

Fallback

FMI 3, 4, 5, 7:

  • Amber Warning lamp on
  • No degraded modes
  • Engine may not crank

FMI 12:

  • Engine cranking prohibited

Conditions to Set Fault Code Inactive

FMI 3: SER circuit not shorted to power for 10 seconds.

FMI 4: SER circuit not shorted to ground for 10 seconds.

FMI 5: SER circuit not open for 10 seconds.

FMI 7: SER wiring issue corrected and ignition key cycle.

FMI 12: Key cycle.

Possible Causes

FMI 3, 4, 5:

  • Start enable type not configured correctly in the TCM
  • SER
    • Internal failure
  • SER circuit wiring
    • Wiring shorted to power, shorted to ground, or open.
    • Terminals may be bent, spread, or corroded.

FMI 7:

  • SER
    • Internal failure
  • SER circuit wiring
    • Incorrectly wired
    • Bypassed or “jumped” circuit wiring

FMI 12:

  • TCM
    • Internal failure
    • Software issue

Note: Refer to OEM for troubleshooting a failed system.

Additional Tools

Digital Volt Ohm Meter

Component Identification

_Graphics/LineArt/TRTS0950_FC120x_ComponentID.png

1. 20-Way TCM Vehicle Harness Connector

2. Transmission Control Module (TCM)

3. 5-Way Start Enable Relay Socket

_Graphics/LineArt/TRTS0950_FC120_WiringID.png

1. Transmission Control Module (TCM)

2. 20-Way TCM Vehicle Harness Connector

3. 5-Way Start Enable Relay Socket

4. 5-Way Start Enable Relay

_Graphics/LineArt/TRTS0990_Wiring-Key.png
_Graphics/LineArt/TRTS0950_FC120_Wiring2.png

Start Enable Relay Circuit States (Normally Open)

1. Open Relay - Key On and Transmission is Unable to Confirm Neutral

2. Open Relay - Key Start and Transmission is Unable to Confirm Neutral

3. Closed Relay - Key On and Transmission Confirmed in Neutral

4. Closed Relay - Key Start and Transmission Confirmed in Neutral

_Graphics/LineArt/TRTS0990_Wiring-Key.png

Fault Code 120 Troubleshooting

A
Purpose:Check for active or inactive fault codes.

  1. Set vehicle parking brake and chock wheels.

  2. Record the transmission fault codes, FMIs, occurrences, and timestamps from the Service Activity Report created during the Diagnostic Procedure.

    Note: If Fault Code 120 is inactive and engine cranks, but does not run, refer to OEM for troubleshooting a failed system.

    Note: Some OEMs and chassis may use an alternate wiring pattern, which may include the use of second relay for other vehicle systems. Consult OEM wiring diagrams.

  • If Fault Code 120 is Inactive and there are other Active vehicle or transmission fault codes, troubleshoot all Active fault codes. Go to Step V

  • If Fault Code 120 FMI 3, 4, or 5 is Active, Go to Step B

  • If Fault Code 120 FMI 3, 4 or 5 is Inactive, Go to Step C

  • If Fault Code 120 FMI 7 is set, Go to Step L

  • If Fault Code 120 FMI 12 is Active or Inactive, Contact Eaton Cummins Automated Transmission Technologies for further diagnostic instructions. For Help Line phone numbers, go to Contact Information. Go to Step V

B
Purpose:Verify Start Enable Relay Type configured in the TCM and installed on the vehicle.

  1. Key off.

  2. Allow TCM to perform a complete power down.

  3. Key on with engine off.

  4. Connect ServiceRanger.

  5. Go to “Configuration”.

  6. Select “Vehicle”.

  7. Record the “Start Enable Type” "Current Value" in table.

  8. Record the “Start Enable Type” installed on the vehicle in table.

    Note: The vehicle's start enable type (Start Enable Relay or J1939) is determined by OEM. Refer to the OEM regarding the start enable type installed on the vehicle.

  9. Compare reading(s) in table.

  • If “Start Enable Type” is not configured correctly, select the correct configuration from the “New Value” drop down, select “Apply” and follow on screen prompt. Go to Step V

  • If FMI 3, 4 or 5 is active and “Start Enable Type” is configured correctly, Go to Step E

LocationStart Enable Type
TCM (ServiceRanger)
Vehicle
C
Purpose:Use Product Diagnostic (PD) Test to locate intermittent failures.

  1. Key on with engine off.

  2. Connect ServiceRanger.

  3. Go To “Service Routines”

  4. Start Product Diagnostic Test and follow on-screen prompts.

    Note: Solid “PD” may appear in display when PD Test is active.

    Note: TCM will not enter PD Test mode when there are Active fault code.

    _Graphics/LineArt/PD_GearDisplay.png

  5. Wiggle the vehicle harness and connections between the charging/battery system and 20-Way TCM Vehicle Harness Connector. Look for signs of rubbing or chafing on the wires. Refer to OEM wiring diagrams.

  6. To end the test, press the stop button.

  • If fault codes set Active while wiggling the vehicle harness, refer to OEM guidelines for repair or replacement of the vehicle harness and/or the 20-Way TCM Vehicle Harness Connector. Go to Step V

  • If no fault codes become Active, Go to Step D

D
Purpose:Verify SER Connector condition.

  1. Key off.

  2. Remove SER from 4-Way relay socket.

  3. Inspect the SER and 4-Way relay socket, verify SER socket is not damaged, is free from contamination and corrosion, and terminals are not bent, spread or loose.

  • If contamination or damage is found, refer to OEM guidelines for repair or replacement of the SER and/or 4-Way relay socket. Go to Step V

  • If no contamination or damage is found, Go to Step E

E
Purpose: Verify SER coil supply voltage.

  1. Key off.

  2. Remove SER.

  3. Inspect SER and connector body for damage, bent, spread, corroded or loose terminals.

  4. Key on with engine off.

  5. Measure voltage between SER socket Pin 86 and Pin 85. Record reading in table.

    Note: SER types may vary, refer to OEM wiring diagrams and connector views.

    _Graphics/LineArt/TRTS0950_FC120_SER85and86.png

  6. Compare reading(s) in table.

PinsRangeReading(s)
85 to 8611–13 V
F
Purpose:Verify SER coil resistance.

  1. Key off.

  2. Measure resistance across the SER Pin 85 and Pin 86. Record reading in table.

    _Graphics/LineArt/TRTS0950_FC120_RelayPin85and86-O.png

  3. Compare reading(s) in table.

  • If readings are in range, Go to Step H

  • If readings are out of range, refer to OEM guidelines for SER replacement. Go to Step V

PinsRangeReading(s)
85 to 8640–200 ohms
G
Purpose:Verify 20-Way TCM Vehicle Harness Connector condition.

  1. Key off.

  2. Disconnect the 20-Way TCM Vehicle Harness Connector.

  3. Inspect the 20-Way TCM Vehicle 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.

  4. Inspect the TCM side of the 20-Way TCM Vehicle 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.

  • If contamination or damage is found, refer to OEM guidelines for repair or replacement of the 20-Way TCM Vehicle Harness Connector. Go to Step V

  • If no contamination or damage is found, Go to Step H

H
Purpose:Verify SER coil control circuits continuity and not shorted together.

  1. Key off.

  2. Measure resistance between 20-Way TCM Vehicle Harness Connector Pin 14 and SER socket Pin 86. Record reading in table.

    _Graphics/LineArt/TRTS0950_FC120_VPin14andSER86.png

  3. Measure resistance between 20-Way TCM Vehicle Harness Connector Pin 4 and SER socket Pin 85. Record reading in table.

    _Graphics/LineArt/TRTS0950_FC120_VPin4andSER85.png

  4. Measure resistance between SER socket Pin 85 and Pin 86. Record reading in table.

    _Graphics/LineArt/TRTS0950_FC120_SER85and86.png

  5. Compare reading(s) in table.

  • If readings are out of range, refer to OEM guidelines for repair or replacement of 20-Way TCM Vehicle Harness. Go to Step V

  • If readings are in range, Go to Step I

PinsRangeReading(s)
14 to 860.0–0.3 Ohms
4 to 850.0–0.3 Ohms
85 to 86Open Circuit (OL)
I
Purpose:Verify SER Negative (-) circuit is not shorted to ground or power.

  1. Key off.

  2. Measure resistance between SER socket Pin 85 and Ground. Record reading.

    _Graphics/LineArt/TRTS0950_FC120_SER85andGND.png

  3. Measure resistance between SER socket Pin 85 and Battery Positive. Record reading.

    _Graphics/LineArt/TRTS0950_FC120_SER85andBATTPOS.png

  4. Compare reading(s) in table.

  • If readings are out of range, refer to OEM guidelines for repair or replacement of 20-Way TCM Vehicle Harness. Go to Step V

  • If readings are in range, Go to Step J

PinsRangeReading(s)
85 to GroundOpen Circuit (OL)
85 to Battery Positive (+)Open Circuit (OL)
J
Purpose:Verify SER Positive (+) circuit is not shorted to ground or power.

  1. Key off.

  2. Measure resistance between SER socket Pin 86 and Ground. Record reading in table.

    _Graphics/LineArt/TRTS0950_FC120_SER86andGND.png

  3. Measure resistance between SER socket Pin 86 and Battery Positive. Record reading in table.

    _Graphics/LineArt/TRTS0950_FC120_SER86andBATTPOS.png

  4. Compare reading(s) in table.

  • If readings are out of range, refer to OEM guidelines for repair or replacement of 20-Way TCM Vehicle Harness. Go to Step V

  • If readings are in range, Go to Step K

PinsRangeReading(s)
86 to GroundOpen Circuit (OL)
86 to Battery Positive (+)Open Circuit (OL)
K
Purpose:Verify fault code status.

  1. Key off.

  2. Reconnect all connectors and verify that all components are properly installed.

  3. Key on with engine off.

  4. Connect ServiceRanger.

  5. Retrieve and record the transmission fault codes, FMIs, occurrences, and timestamps.

  • If Fault Code 120 is Inactive, no problem was found. The intermittent nature of the fault makes it likely that the problem is between the SER Socket and 20-Way TCM Vehicle Harness Connector. Refer to OEM guidelines for repair or replacement of 20-Way TCM Vehicle Harness. Go to Step V

  • If Fault Code 120 is Active and no fault was found with the vehicle SER wiring, replace the Transmission Control Module (TCM). Go to Step V

    Note: Troubleshooting indicates no fault found with the wiring or connections to the TCM. Ensure an intermittent issue does not exist with the wiring or connections.

L
Purpose:Verify if fault was inadvertently set.

  1. Key off.

  2. Verify SER is properly installed and wired, refer to OEM wiring diagrams and connector views.

    Note: Fault Code 120 FMI 7 sets Active only during engine cranking.

  3. Key on with engine off

  4. Connect ServiceRanger.

  5. Attempt to crank engine.

  6. Retrieve and record the transmission fault codes, FMIs, occurrences, and timestamps.

  • If Fault Code 120 FMI 7 is Inactive and the engine cranks, SER may have been incorrectly wired and repaired or bypassed (jumped). Test complete. Go to Step V

  • If Fault Code 120 FMI 7 sets Active, Go to Step M

M
Purpose:Verify SER latch control circuits are not shorted together.

  1. Key off.

  2. Remove SER.

  3. Measure resistance between SER socket Pin 30 and Pin 87. Record reading in table.

    Note: SER types may vary, refer to OEM wiring diagrams and connector views.

    _Graphics/LineArt/TRTS0950_FC120_SER30and87.png

  4. Compare reading(s) in table.

  • If readings are out of range, refer to OEM guidelines for repair or replacement of the SER latch control circuits. Go to Step V

  • If readings are in range, Go to Step N

PinsRangeReading(s)
30 to 87Open Circuit (OL)
N
Purpose:Verify SER latch (internal) is not shorted closed.

  1. Key off

  2. Measure resistance across the SER Pin 30 and Pin 87. Record reading in table.

    _Graphics/LineArt/TRTS0950_FC120_SERPin30and87.png

  3. Compare reading(s) in table.

  • If readings are out of range, refer to OEM guidelines for SER replacement. Go to Step V

  • If readings are in range, Go to Step V

PinsRangeReading(s)
30 to 87Open Circuit (OL)
V
Purpose:Verify repair.

  1. Key off.

  2. Reconnect all connectors and verify that all components are properly installed.

  3. Key on with engine off.

  4. Connect ServiceRanger.

  5. Go to “Fault Codes”.

  6. Select “Clear All Faults”.

  7. Operate vehicle and attempt to reset the fault code or duplicate the previous complaint.

  8. Check for fault codes using ServiceRanger.