Fault Code 986: Two Speed Axle Switch
J1939: SA 3 SPN 4056 FMI 4, 12, 13, 14, 20
Overview
The Endurant XD Series transmission can be combined with a 2-speed axle for additional gear ratio coverage. When 2-speed axle operation is required the Transmission Control Module (TCM) receives an axle gear engagement signal (Input) then adjusts the transmission shift strategy and launch characteristics for the new axle gear ratio. Reference Endurant XD Driver Instructions TRDR0960 for Two-Speed Axle operation.
The TCM can be configured for operation with a 2-speed axle with messages over the vehicle Primary Data Link J1939A or from a switch circuit hardwired directly to the TCM. The TCM is equipped to receive 4 switch inputs and control 3 relay outputs that can be configured in an Input/Output (I/O) Package to support various vocational features.
If the TCM is configured to "2-Speed Axle - J1939", axle gear engagement messages are provided to the TCM by an OEM vehicle ECU. If the TCM is configured to "2-Speed Axle - TCM Hardwired", an axle gear engagement notification signal (Input) is provided to the TCM from a hardwired switch circuit.
The 2-speed axle circuit input is connected to the TCM in the 20-Way TCM Body Harness Connector. The 2-speed axle circuit is installed by the OEM or body builder. Reference Input / Output Calibration in the Appendix for recommended 2-speed axle circuit wiring diagrams.
Detection
The TCM monitors the Two Speed Axle Switch hardwired circuit input signal. If the signal is out of range, the fault is set Active.
Conditions to Set Fault Code Active
FMI 4 – Voltage Below Normal or Shorted Low: Two Speed Axle Switch circuit input signal shorted to ground for 5 seconds.
FMI 12 – Bad Intelligent Device: TCM has detected an internal processing error.
FMI 13 – Out of Calibration: The TCM detected invalid I/O Package calibration.
FMI 14 – Special Instructions: The TCM detected invalid I/O Package calibration.
FMI 20 – Data Drifted High: Two Speed Axle Switch circuit input signal out of range (4.00–5.25 V) for 5 seconds.
Fallback
All FMIs:
- Amber warning lamp on
- No degraded modes
- 2-Speed Axle operation may not function
Conditions to Set Fault Code Inactive
FMI 4: Two Speed Axle Switch circuit not shorted to ground for 10 seconds.
FMI 12: Key cycle and fault condition no longer exits.
FMI 13, 14: Valid I/O Package calibration file is configured in TCM.
FMI 20: Two Speed Axle Switch circuit input signal in range for 10 seconds.
Possible Causes
FMI 4, 20:
- Vehicle Harness - Two Speed Axle Switch Circuit
- Shorted to power, shorted to ground or open circuit
FMI 12:
- TCM
- Internal failure
- Software issue
FMI 13, 14:
- TCM
- Invalid I/O Package calibration file configured in TCM
Fault Code 986 Troubleshooting
Set vehicle parking brake and chock wheels.
Record transmission fault codes, FMIs, occurrences, and timestamps from Service Activity Report created during the Diagnostic Procedure.
If Fault Code 986 is Inactive and there are other Active vehicle or transmission fault codes, troubleshoot all Active fault codes. Go to Step V
If Fault Code 986 FMI 4, 20 is Active, Go to Step B
If Fault Code 986 FMI 4, 20 is Inactive, the intermittent nature of the fault makes it likely that the problem is in the Two Speed Axle Switch circuit. Go to Step C
Note: Two Speed Axle Switch circuit wiring is installed by OEM or body builder.
If Fault Code 986 FMI 12 is Active, replace Transmission Control Module (TCM). Go to Step V
If Fault Code 986 FMI 12 is Inactive, Go to Step V
If Fault Code 986 FMI 13 or 14 is Active, Contact Eaton Cummins Automated Transmission Technologies for further diagnostic instructions. For Help Line phone numbers, go to Contact Information. Go to Step V
If Fault Code 986 FMI 13 or 14 is Inactive, Go to Step V
Key on.
Connect ServiceRanger.
Go To “Configuration”.
Select “Vehicle”.
Record "Multi-Speed Driveline Configuration" Current Value.
If "Multi-Speed Driveline Configuration" Current Value indicates "Not Installed" and Two Speed Axle Switch circuit is properly installed and wired, select "2-Speed Axle - TCM Hardwired" option and follow on-screen prompts. Go to Step V
If "Multi-Speed Driveline Configuration" Current Value indicates a "2-Speed Axle - TCM Hardwired" option and Two Speed Axle Switch circuit is properly installed and wired, Go to Step C
Key on with engine off.
Connect ServiceRanger.
Go To “Configuration”.
Select “Calibrations” tab.
Record "I/O Package" Current Value.
Based on I/O package configured refer to I/O circuit schematic indicated in table. Contact OEM or body builder for repair or replacement of Two Speed Axle Switch signal circuit. Go to Step V
Note: Two Speed Axle Switch signal circuit wiring is installed by OEM or body builder.
| Fault Code 986: Two Speed Axle Switch | ||||
|---|---|---|---|---|
| Package # and Description | 20-Way TCM Body Connector Pin(s) | Component(s) | ||
| Input / Output Calibration Package 16: 2-Speed Axle | 5 | 6 | Normally Open Pressure Switch | 2-Speed Vehicle Controls High Range Air Line |
| Input / Output Calibration Package 17: 2-Speed Axle + Rock Free Mode | 5 | 6 | ||
| Input / Output Calibration Package 18: 2-Speed Axle + PTO 1 | 6 | 14 | ||
| Input / Output Calibration Package 19: 2-Speed Axle + Secondary Shift Mode | 5 | 6 | ||
| Input / Output Calibration Package 33: 2-Speed Axle + Reverse Output | 5 | 6 | ||
Key off.
Reconnect all connectors and verify 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 vehicle operates properly, test complete.
If Fault Code 986 sets Active, Go to Step A
If a fault code other than 986 sets Active, troubleshoot per the Fault Code Isolation Procedure Index.