Endurant XD
TRTS0960 EN-US
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September 2024 - A

Fault Code 168: Brake Primary Pressure

J1939: SA 3 SPN 117 FMI 9, 13, 18, 19

Overview

The Transmission Control Module (TCM) receives the vehicle’s Brake Primary Tank Pressure message from a vehicle Electronic Control Unit (ECU) over the Primary Data Link (J1939A). The Brake Primary Tank Pressure message is used as a secondary vehicle air pressure input by the TCM to ensure adequate air pressure is maintained for transmission operation.

Note: The vehicle air supply comes from a dedicated transmission air tank. The primary and secondary air gauges in the cab of the vehicle may not reflect the pressure of the transmission air supply line. The transmission air tank is often isolated from the rest of the vehicle air system with a Pressure Protection Valve and/or Check Valve.

Detection

The TCM monitors Brake Primary Tank Pressure messages. If messages are not received or are invalid, the fault is set Active.

Conditions to Set Fault Code Active

FMI 9 - Abnormal Update Rate: Brake Primary Tank Pressure message not received for 10 seconds.

FMI 13 - Out of Calibration: Brake Primary Tank Pressure message not available for 10 seconds.

FMI 18 - Data Valid but Below Normal (Moderately Severe): Brake Primary Tank Pressure and Transmission Air Supply Pressure reported greater than 90 psi (6.2 bar) and then fell below 80 psi (5.5 bar) with the vehicle stationary and the transmission in Neutral.

FMI 19 – Received Network Data In Error: Brake Primary Tank Pressure messages invalid for 10 seconds.

Fallback

FMI 9, 13, 19:

  • Amber warning lamp on
  • No degraded modes

FMI 18:

  • Coast Mode and Neutral Coast prohibited
  • Urge to Move and Creep Mode prohibited
  • Inertia Brake activation prohibited
  • Upshifts prohibited
  • Clutch disengagements prohibited
  • Non-Neutral modes prohibited
  • PTO mode prohibited

Conditions to Set Fault Code Inactive

FMI 9, 13, 19: Brake Primary Tank Pressure messages received and valid for 10 seconds.

FMI 18: Brake Primary Tank Pressure above 90 psi.

Possible Causes

FMI 9, 13, 19:

  • Vehicle Components
    • Primary Brake Tank Pressure message not enabled
    • Other vehicle ECU(s) faulted
  • Vehicle Harness - Primary Data Link (J1939A)
    • Wiring shorted to power, shorted to ground or open
    • Terminals bent, spread, corroded, or loose

FMI 18:

  • Vehicle Components
    • Air system

Note: Refer to OEM for troubleshooting a failed system.

Additional Tools

  • None

Fault Code 168 Troubleshooting

A
Purpose:Check for Active or Inactive fault codes.

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

  • If Fault Code 168 is Inactive and there are other Active vehicle or transmission fault codes, troubleshoot all Active fault codes. Go to Step V

  • If Fault Code 168 FMI 9, 19 is Active or Inactive, Go to Step B

  • If Fault Code 168 FMI 13 is Active, refer to OEM and enable vehicle Brake Primary Tank Pressure message (SPN 117). Go to Step V

  • If Fault Code 168 FMI 13 is Inactive, Go to Step V

  • If Fault Code 168 FMI 18 is Active or Inactive, Go to Step C

B
Purpose:Monitor Brake Primary Tank Pressure and vehicle air pressure.

  1. Key on with engine running.

  2. Allow air pressure to build to governor cut off.

  3. Key off.

  4. Key on with engine off.

  5. Connect ServiceRanger.

  6. Go To “Data Monitor”.

  7. Select “Pressure”.

  8. Select “Brake primary pressure”.

  9. Select all “- 117” SPN sources.

    Note: Not all sources will indicate a value.

  10. Monitor 117 - Brake primary pressure value. Record reading in table.

  11. Monitor vehicle in-dash air pressure gauge. Record reading in table.

  12. Compare reading(s) in table.

  • If readings are out of range, refer to OEM guidelines for repair or replacement of vehicle air system or Brake Primary Tank Pressure message (SPN 117). Go to Step V

  • If readings are in range and no fault was found, the intermittent nature of the fault makes it likely that the problem is in vehicle air system or Brake Primary Tank Pressure message (SPN 117). Contact OEM for further diagnostic instructions. Go to Step V

Parameter/ SourceRangeReading(s)
117 - Brake primary pressureWithin 0-20 psi of Vehicle air pressure
Vehicle in-dash primary air pressure gauge100-135 psi
C
Purpose:Monitor Brake Primary Tank Pressure, Transmission Air Supply Pressure and vehicle air pressure.

  1. Key on with engine running.

  2. Allow air pressure to build to governor cut off.

  3. Key off.

  4. Key on with engine off.

  5. Connect ServiceRanger.

  6. Go To “Data Monitor”.

  7. From “Default Parameter Files” tab, select “Transmission Pressure”.

  8. Monitor 520524 - Line Pressure Feedback value. Record reading in table.

  9. Select “Pressure”.

  10. Select “Brake primary pressure”.

  11. Select all “- 117" SPN sources.

    Note: Not all sources will indicate a value.

  12. Monitor 117 - Brake primary pressure value. Record reading in table.

  13. Monitor vehicle in-dash air pressure gauge. Record reading in table.

  14. Compare reading(s) in table.

  • If readings are out of range, refer to OEM guidelines for repair or replacement of vehicle air system. Go to Step V

  • If readings are in range and no fault was found, the intermittent nature of the fault makes it likely that the problem is in vehicle air system. Contact OEM for further diagnostic instructions. Go to Step V

Parameter/ SourceRangeReading(s)
520524 - Line Pressure FeedbackWithin 0–20 psi of Vehicle air pressure
117 - Brake primary pressureWithin 0–20 psi of Vehicle air pressure
Vehicle in-dash primary air pressure gauge100–135 psi
V
Purpose:Verify Repair.

  1. Key off.

  2. Reconnect all connectors and verify 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.