Endurant HD
TRTS0950 EN-US
|
November 2024 - B

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 Pressure signal message over the Primary Data Link. The Brake Primary Pressure signal is used as a secondary vehicle air pressure input by the TCM to ensure air pressure is adequate 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 the Brake Primary Pressure signal. If the message is not received or invalid, the fault is set active.

Conditions to Set Fault Code Active

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

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

FMI 18 - Data Valid but Below Normal (Moderately Severe): Brake Primary 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: Brake Primary Pressure message invalid for 10 seconds.

Fallback

FMI 9, 13, 19:

  • Amber warning lamp on
  • No degraded performance

FMI 18:

  • Non-neutral modes prohibited
  • PTO mode prohibited

Conditions to Set Fault Code Inactive

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

FMI 18: Brake Primary Pressure above 90 psi.

Possible Causes

FMI 9, 13, 19:

  • Vehicle Components
    • Module(s)
    • Brake Primary Pressure Sensor
    • Primary Data Link

FMI 18:

  • Vehicle Components
    • Air system

Additional Tools

  • None

Fault Code 168 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.

  • 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 13 is Active, refer to OEM and enable vehicle Brake Primary Pressure SPN 117. Go to Step V

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

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

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

B
Purpose:Monitor Brake Primary 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 of the “- 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 the vehicle air system or Brake Primary Pressure signal. Go to Step V

  • If readings are in range, no fault was found. The intermittent nature of the fault makes it likely that the problem is in the vehicle air system or Brake Primary Pressure signal message. 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 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 the “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 of the “- 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 the vehicle air system. Go to Step V

  • If readings are in range, no fault was found. The intermittent nature of the fault makes it likely that the problem is in the 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 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.