P079A
DTC P079A
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
DTC Descriptor
DTC P079A
- Transmission Clutch 1 Slip Detected
Typical Scan Tool Data
Circuit/System Description
The transmission control module (TCM) monitors the Clutch 1 Slip Speed for each Hybrid Trans. Mode Commanded state. This DTC detects clutch slip when the Variable Low 1-2 reverse clutch is applied.
Conditions for Running the DTC
* The clutch PC solenoid 3 commanded pressure is 1800 kpa (261 psi) for 1 second.
* The commanded gear is:
- Reverse
- EVT Mode 1
- Gear 1
- Gear 2
Conditions for Setting the DTC
The TCM detects the variable low 1-2 reverse clutch slip greater than 300 RPM for 3 seconds.
Action Taken When the DTC Sets
* P079A is a Type A DTC.
* The TCM inhibits Reverse, EVT Low, Gear 1 and Gear 2.
Conditions for Clearing the DTC
P079A is a Type A DTC.
Diagnostic Aids
When attempting to set transmission performance DTCs, observe the Freeze Frame and Failure Records to assist in duplicating the failure conditions. Ensure the transmission fluid level is correct and there are no leaks. Hard acceleration may be required to induce the fault. If there are any other transmission DTCs set, diagnose those first.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Circuit/System Verification
1. Verify that DTCs P0721, P0722, P0723, P0966, P0967, P0969, P0970, P0971, P0973, P0974, P0976, P0977, P2720, P2721, P2728, P2729, or P2730 are not set.
• If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions).
2. Clear the DTC.
3. Perform the Transmission Fluid Check (Transmission Fluid Check) to verify correct fluid level and condition. The transmission fluid level should be within the crosshatch band and the transmission fluid should be red or dark brown.
• If the transmission fluid is low or discolored, refer to Transmission Fluid Replacement (Removal and Replacement).
4. Engine idling at operating temperature. Attempt to clean or free up a potential sticking valve with the scan tool Service Cleaning Procedure. Refer to Control Solenoid Valve and Transmission Control Module Assembly Cleaning (Control Solenoid Valve and Transmission Control Module Assembly Cleaning) for further instructions.
5. Operate the vehicle from 1st through 4th gear while observing the Clutch 1 Slip Speed parameter. Stop the vehicle and turn the ignition OFF for 30 seconds. The Clutch 1 Slip Speed parameter should display 0 RPM when the Clutch 1 Status parameter displays Applied.
• If any other transmission DTCs are set, diagnose those first.
• If the DTC P079A resets, go to Component Testing.
Component Testing
1. Perform the Line Pressure Check (Line Pressure Check).
2. Perform the Control Solenoid Valve and Transmission Control Module Assembly Solenoid Performance Test (Control Solenoid Valve and Transmission Control Module Assembly Solenoid Performance Test).
• If a concern is found, replace the control solenoid (w/body and TCM) valve assembly.
3. Inspect the trans fluid pump ball check valve for possible sticking or damage.
• If you found a concern with this check ball, repair the concern.
4. Inspect the aux fluid pump cutoff valve, and the fluid pump cutoff valve for possible sticking or damage.
• If you found a concern with the variable low 1-2 clutch regulator valve, repair or replace the valve or valve body.
5. Inspect the variable low, 1-2 reverse clutch assembly for wear or damage.
• If you found a variable low, 1-2 reverse clutch assembly concern, repair or replace the low and reverse clutch assembly as necessary.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Variable Low and 1-2 Reverse Clutch Piston Removal (Overhaul) and Variable Low and 1-2 Reverse Clutch Piston Installation (Overhaul) for assembly repair or replacement
* Control Valve Lower Body and Upper Body Replacement (2MT70 - Automatic Transmission) for lower valve body assembly replacement
* Control Module References (Programming and Relearning) for control solenoid (w/body and TCM) valve assembly replacement, setup, and programming
* Transmission Replacement (Removal and Replacement) for transmission removal