Fault Code 126: Secondary ADS Operation Status
J1939: SA 3 SPN 20874 FMI 9, 13, 14, 19
Overview
The Transmission Control Module (TCM) receives the vehicle’s primary Automated Driving System (ADS) Operation Status message from a vehicle Electronic Control Unit (ECU) over the Primary Data Link (J1939A). This information is used to determine transmission operation.
The TCM also receives a secondary Automated Driving System (ADS) Operation Status message from a vehicle Electronic Control Unit (ECU) over the Primary Data Link (J1939A). This redundancy allows the TCM to maintain transmission function in a degraded mode in the event either message is not available.
Detection
The TCM monitors secondary ADS Operation Status 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: Secondary ADS Operation Status message not received for 5 seconds.
FMI 13 - Out of Calibration: Secondary ADS Operation Status messages not available for 5 seconds.
FMI 14 - Special Instructions: Primary and Secondary ADS Operation Status messages do not match for 5 seconds.
FMI 19 - Received Network Data in Error: Secondary ADS Operation Status messages invalid for 5 seconds.
Fallback
FMI 9, 13, 14, 19:
If fault codes 125 and 126 are Active:
- Amber warning lamp on
- ADS Operation prohibited
Conditions to Set Fault Code Inactive
FMI 9, 13, 19: Secondary ADS Operation Status messages received and valid for 10 seconds.
FMI 14: Primary and Secondary ADS Operation Status messages match for 1 second.
Possible Causes
FMI 9, 13, 14, 19:
- Vehicle Components - Vehicle ECU(s)
- Secondary ADS Operation Status message not enabled
- Other vehicle ECU(s) faulted
- Vehicle Harness - Primary Data Link (J1939A)
- Shorted to power, shorted to ground or open circuit
- Terminals bent, spread, corroded, or loose
Note: Refer to OEM for troubleshooting a failed system.
Additional Tools
- None
Fault Code 126 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 126 is Inactive and there are other Active vehicle or transmission fault codes, troubleshoot all Active fault codes. Go to Step V
If Fault Code 126 FMI 9, 14, 19 is Active or Inactive, refer to OEM guidelines for repair of the vehicle secondary ADS Operation Status message (SPN 20874). Go to Step V
If Fault Code 126 FMI 13 is Active, refer to OEM and enable vehicle Secondary ADS Operation Status message (SPN 20874). Go to Step V
If Fault Code 126 FMI 13 is Inactive, Go to Step V
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 126 sets Active, Go to Step A
If a fault code other than 126 sets Active, troubleshoot per Fault Code Isolation Procedure Index.