Transmission Control Module (TCM) - NAG1

U1401-IMPLAUSIBLE ENGINE SPEED SIGNAL RECEIVED

For a complete wiring diagram, refer to the Wiring Information.

Theory of Operation

The messages sent on the CAN bus are distinguished by an identifier (ID). Each CAN ID is defined to contain a certain number of bytes. The Transmission Control Module (TCM) verifies that it has received the proper number of bytes for each ID.

- When Monitored:
Continuously with the ignition on, one valid CAN ID received at least once, and no U0002-CAN Bus Off Performance DTC present.

- Set Condition:
When the TCM detects an incorrect CAN ID from the ECM/PCM.





Always perform the NAG1 Pre-Diagnostic Troubleshooting procedure before proceeding. NAG1 Pre-Diagnostic Troubleshooting Procedure.

1. CHECK FOR BCM CAN BUS DTCS
1. With the scan tool, read BCM DTCs.

Are there any BCM CAN BUS DTCs present?

Yes

- Testing and Inspection Perform the appropriate diagnostic procedure. Perform the diagnostic procedure for DTC U0001-CAN C BUS first.
- Perform the NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test.

No

- Go To 2

2. CHECK IF ENGINE DTCS ARE PRESENT
1. With the scan tool, read engine DTCs.

Are there any engine DTCs present?

Yes

- Perform the appropriate diagnostic procedure.
- Perform the NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test.

No

- Using the schematics as a guide, check the Transmission Control Module (TCM) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace and program the TCM.
- Perform the NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test.