NAG1 Automatic Transmission

P0720 - CAN BUS CIRCUIT





When Monitored and Set Condition

- When Monitored: Always monitored with system active at each ignition cycle.
- Set Condition: Open circuit in the CAN C BUS (+) circuit or CAN C BUS (-) circuit, short to ground of CAN C BUS (+) circuit or CAN C BUS (-) circuit, short to voltage of CAN C BUS (+) circuit or CAN C BUS (-) circuit, CAN C BUS (+) circuit shorted to CAN C BUS (-) circuit, or a TCM failure.

Note: All CAN message missing DTCs will also be present, which indicates a complete BUS failure.






Diagnostic Test


1. PRE-DIAGNOSTIC CHECK OUT





NOTE: Low fluid level can be the cause of many transmission problems. If the fluid level is low, locate and repair the leak then check and adjust the fluid level.

NOTE: Always perform diagnostics with a fully charged battery to avoid false symptoms.

With the DRB III(R), read Engine DTCs. Check and repair all engine DTCs prior to performing transmission symptom diagnostics.

With the DRB III(R), read and record all Transmission DTCs.


NOTE: Check connectors - Clean/repair as necessary. Poor pin to terminal connections can set DTCs.

Using the wiring diagram/schematic as a guide, inspect the wiring and connectors. Repair as necessary.

Most DTCs set on start up but some must be set by driving the vehicle such that all diagnostic monitors have run.


NOTE: Check for any Technical Service Bulletins that may apply.

Perform this procedure prior to Symptom diagnosis.

Continue

Go To 2



2. CAN C BUS (+) AND/OR CAN C BUS (-) CIRCUIT OPEN





NOTE: If the CAN BUS CIRCUIT DTC is present, all the CAN MESSAGE MISSING DTCs will be set also. Ignore the Missing Message DTCs and perform the CAN BUS CIRCUIT DTC test.

Turn the ignition off.

Disconnect the TCM C3 harness connector.

Disconnect the PCM C4 harness connector.

Disconnect the CAB harness connector.


NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance of both the CAN C BUS (+) circuit and the CAN C BUS (-) circuit from the TCM C3 harness connector and to both the PCM C4 harness connector and to the CAB harness connector.

Is the resistance of each BUS circuit below 5.0 ohms?

Yes

Go To 3

No

- Repair the faulty CAN C BUS circuit for an open.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test



3. CAN C BUS (+) SHORT TO CAN C BUS (-)





With the ignition off.

Measure the resistance between the CAN C BUS (+) circuit and the CAN C BUS (-) circuit at the TCM C3 harness connector.

Is the resistance above 100 kohms?

Yes

- Go To 4

No

- Repair the CAN C BUS (+) circuit for a short to the CAN C BUS (-) circuit.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test



4. CAN C BUS (+) AND/OR CAN C BUS (-) CIRCUIT SHORT TO GROUND





With the ignition off.

Measure the resistance between ground and both the CAN C BUS (+) circuit and the CAN C BUS (-) circuit.

Is the resistance above 100 kohms for both BUS circuits?

Yes

- Go To 5

No

- Repair the faulty CAN C BUS circuit for a short to ground.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test



5. CAN C BUS (+) AND/OR CAN C BUS (-) CIRCUIT SHORT TO ANOTHER CIRCUIT





With the ignition off.

Measure the resistance from both the CAN C BUS (+) circuit and the CAN C BUS (-) circuit to all other circuits in the TCM C3 and C2 harness connector.

Is the resistance above 100 kohms for all measurements?

Yes

- Go To 6

No

- Repair the CAN C BUS (+) and/or CAN C BUS (-) circuit for a short to other circuits.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test



6. PCM - CAN BUS CIRCUIT





With the ignition off.

Reconnect the TCM C3 harness connector.

Reconnect the CAB harness connector.

Measure the resistance from the CAN C BUS (+) circuit to the CAN C BUS (-) circuit at the PCM C4 harness connector.

Is the resistance 60.0 ohms, ±3.0 ohms?

Yes

- Replace and program the Powertrain Control Module.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

Go To 7



7. CAB - TERMINATING RESISTOR





With the ignition off.

Reconnect the PCM C4 harness connector.

Disconnect the CAB harness connector.


NOTE: Check connectors - Clean/repair as necessary.

Measure the resistance from the CAN C BUS (+) circuit to the CAN C BUS (-) circuit at the CAB harness connector.

Is the resistance 120 ohms, ±2.0 ohms?

Yes

- Replace the Controller Antilock Brake.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test

No

- Replace the Transmission Control Module.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. Transmission Verification Test