P0979

P0979-SHIFT SOLENOID C CONTROL CIRCUIT LOW

For a complete wiring diagram Refer to the Wiring Information.

Theory of Operation

The purpose of the monitoring is to detect circuit failures on any of the output stages in the Transmission Control Module Assembly (TCMA). All output stages are controlled by a current controller that can operate an output stage in two different modes. Current controlled mode pressure regulators and switched mode or PWM controlled solenoids.

Pressure Regulator Monitoring: The current regulator in the TCM indicates the following circuit failures to the CPU. Short to battery, bypass to ground (high resistance short to ground) and short to ground or open circuit (can only be distinguished when the output stage is in idle mode, i.e. commanded current is 0 mA) In addition to the circuit failure information, the TCM monitoring software uses a PWM feedback signal generated by the current regulator in the output stage to identify failures. To perform rationality monitoring of the output stage current, the TCM software calculates the actual current dependent on the PWM feedback signal, the output stage power supply voltage and the actual transmission oil temperature. The TCM can only distinguish between a short to ground and an open circuit failure if the output stage is deactivated. Depending on the required time to bring the transmission into a limp home mode, a further evaluation of the failure is determined after switching off the output stage in order to distinguish between both failure types.

Solenoid Monitoring: The TCM measures the actual solenoid voltages and compares them to calibrated table to identify the following electrical failures. Short to battery, open circuit and short to ground in case the solenoid is switched on (i.e. commanded control value is 100%), the diagnostic can not distinguish between short to ground and open circuit. In that case the TCM status information is used to detect the failure.

- When Monitored:
Continuously after the ignition switch is turned to the run position.

- Set Condition:
A failure is detected if one of the following conditions occurs. A short to battery failure is detected if the voltage output signal during PWM duty phase is greater than a calibrated threshold. An open circuit failure is detected if the voltage of the output signal during PWM duty cycle is in an invalid range. A short to ground failure is detected if the voltage of the output signal during PWM duty cycle is less than a calibrated threshold. A short to ground or open circuit failure is detected if the commanded duty cycle for the solenoid is 100% and the TCM indicates the output stage is switched off.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. 8HP45 Pre-Diagnostic Troubleshooting Procedure

1. CHECK IF DTC IS CURRENT

NOTE: The Transmission Control Module stores under Environmental Data the transmission operating conditions when the DTC was set. Before clearing any DTCs, record all information pertaining to the DTC.

1. With the scan tool, CLEAR transmission DTCs.
2. Using the Environmental Data previously recorded, drive the vehicle and try to duplicate the condition in which the DTC set.

Does the DTC reset?

Yes

- Go To 2

No

- Go To 3

2. TRANSMISSION CONTROL MODULE ASSEMBLY (TCMA)

If there are no possible causes remaining, view repair.

Repair

- Using the schematics as a guide, check the TCMA terminals for corrosion, damage or terminal push out. Pay particular attention to power and ground circuits. Check Service Information Tune-ups or Service Bulletins for possible causes that may apply. Remove the transmission oil pan and the TCMA. Valve Body - Removal. Inspect and clean the Shift Solenoid C terminals at the wiring harness leadframe for metallic contamination. Reinstall the TCMA. Valve Body - Installation. Connect the scan tool and clear the DTCs. Road test the vehicle and check for DTCs. If the DTC returns, replace and program the TCM. Valve Body - Removal.
- Perform the TRANSMISSION VERIFICATION TEST. Verification Tests.

3. INTERMITTENT WIRING AND CONNECTORS
1. The conditions necessary to set this DTC are not present at this time.
2. Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
3. Wiggle the wiring and connectors while checking for any possible open or shorted circuits.
4. Check for any Service Information Tune-ups or Technical Service Bulletins that may apply.

Were any problems found?

Yes

- Repair as necessary.
- Perform the TRANSMISSION VERIFICATION TEST. Verification Tests.

No

- Test Complete.