P0756
DTC P0756
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptor
DTC P0756
- Shift Solenoid Valve 2 Performance - Stuck Off
Circuit/System Description
Shift solenoid valve 2 is part of the control solenoid valve assembly, which has no serviceable components. Shift solenoid valve 2 is a normally closed solenoid valve and controls fluid to the clutch select valve 3. The transmission control module (TCM) operates the solenoid by turning the low side driver ON or OFF. When the shift solenoid valve 2 is commanded OFF, the plunger forces the metering ball against the actuator feed limit seat, blocking the flow and any existing pressure is exhausted through the exhaust port. When shift solenoid valve 2 is commanded ON, the internal plunger moves and allows the metering ball to move away from the feed seat and against the exhaust seat, creating signal fluid pressure. The signal fluid acts against the clutch select valve 3 to overcome the valve spring force, moving it to the apply position. Shift solenoid valve 2 is commanded OFF in Reverse, and commanded ON in Park, Neutral, Drive 1 Engine Braking, and Drive 1-6 gear ranges.
Conditions for Running the DTC
* DTC P0101, P0102, P0103, P0106, P0107, P0108, P0171, P0172, P0174, P0175, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0401, P042E, P0716, P0717, P0722, P0723, or P182E is not set.
* Engine speed is 400-7,500 RPM for 5 s.
* High side driver is enabled.
* Ignition voltage is greater than 8.5 V.
* Throttle position signal is valid.
* Transmission fluid temperature is -6.6°C (20°F) or greater.
* Output shaft speed is 36 RPM or greater, or the throttle position is 0.5 percent or greater
Conditions for Setting the DTC
* Commanded Gear is 1st locked.
* Gearbox Slip is 400 RPM or greater for 3 s.
* If above conditions exist, the TCM commands second gear. If the gear ratio is between 2.72-3.01 for 1 s, the counter will increment. DTC will set after 3 occurrences.
Action Taken When the DTC Sets
* DTC P0756 is a Type A DTC.
* TCM inhibits Tap Up/Down function.
* TCM inhibits manual shifting of forward gears.
* TCM commands maximum line pressure.
* TCM freezes transmission adaptive functions.
* TCM commands second gear if output speed is less than 1,350 RPM, or neutral if output speed is 1,350 RPM or greater.
Conditions for Clearing the DTC
DTC P0756 is a Type A DTC.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics 6T70 (M7W) - Automatic Transmission
Connector End View Reference
* Component Connector End Views Sunshade - Left
* Inline Harness Connector End Views X110
Description and Operation
* Transmission General Description Transmission General Description
* Transmission Component and System Description Transmission Component and System Description
* Electronic Component Description Electronic Component Description
* Drive Range, First Gear Engine Braking Drive Range, First Gear Engine Braking
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Verification
Note: If other DTCs are set, diagnose those DTCs first.
1. Engine idling, transmission in Park, with parking brake applied and drive wheels chocked.
2. Verify the transmission fluid level and condition is correct. Refer to Transmission Fluid Level and Condition Check Transmission Fluid Level and Condition Check.
• If the transmission fluid level and condition is not correct
Repair as necessary.
• If the transmission fluid level and condition is correct
3. Ignition ON, clear the TCM DTCs with a scan tool.
4. Engine running, brakes applied, transmission gear shift selector in Reverse. Shift to Drive and accelerate to 56 km/h (35 mph) with the scan tool Calculated Throttle Position greater than 15 %. Perform this test 5 consecutive times.
5. Verify DTC P0756 did not set.
• If DTC P0756 sets
Refer to Circuit/System Testing.
• If DTC P0756 did not set
6. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
7. Verify the DTC does not set.
• If the DTC sets
Refer to Circuit/System Testing.
• If the DTC does not set
8. All OK.
Circuit/System Testing
1. Engine idling at the normal operating temperature.
2. Verify the transmission line pressures are within the specified range. Refer to Line Pressure Check Line Pressure Check and Solenoid Valve Pressure Solenoid Valve Pressure.
• If the pressures are not within range
Refer to Fluid Pressure High or Low Fluid Pressure High or Low.
• If the pressures are within range
3. Ignition OFF, remove the Q8 Control Solenoid Valve Assembly.
4. Verify the pressure changes for all solenoids when performing the solenoid test. Refer to Control Solenoid Valve and Transmission Control Module Assembly Solenoid Performance Test Control Solenoid Valve and Transmission Control Module Assembly Solenoid Performance Test.
• If the pressure does not change
Replace the Q8 Control Solenoid Valve Assembly.
• If the pressure changes
5. Verify the mechanical conditions listed below do not exist. Repair or replace as necessary.
Upper Control Valve Body
* Clutch select valve 3 stuck from debris, sediment, binding or scored bore
* Clutch select valve 3 bore plug undersized causing a leak - plug should be a valve fit in the bore.
* Check ball #3 - missing, damaged or malformed, or damage to the seat causing leakage.
Channel Plate and Spacer Plate
Oil channels or orifices blocked by debris.
Mechanical Diode
Broken or not capable of holding torque.
Pump Assembly
Fluid pump vanes or fluid pump rotor broken
Pump Seal
Seal is torn or cut, causing a small leak that is overcome with enough speed and pump capacity.
Q8 Control Solenoid Valve Assembly
* Shift solenoid 2 not pressurizing - stuck OFF or leaking.
* Valve body filter plate assembly cracked, blocked, or damaged gasket seal.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repairs.
* Perform the Reset Transmission Adapts Reset Transmission Adapts following all transmission repairs.
* Control Valve Upper Body Assembly Cleaning and Inspection Control Valve Upper Body Assembly Cleaning and Inspection
* Control Module References Control Module References for control solenoid valve assembly replacement, programming, and setup.