Circuit Description
The 2-3 Shift Solenoid Valve (2-3 SS Valve) controls the fluid flow
acting on the 2-3 shift valves. The solenoid is a normally-open exhaust valve.
With the 1-2 Shift Solenoid Valve (1-2 SS Valve), the 2-3 SS Valve allows
four different shifting combinations.
When the VCM detects a 1-2-2-1 or a 4-3-3-4 shift pattern, depending
on the state of the mechanical failure, then DTC P0756 sets. DTC P0756 is
a type A DTC.
Conditions for Setting the DTC
| • | No TP Sensor DTCs P0122 or P0123. |
| • | No VSS Assy. DTCs P0502 or P0503. |
| • | No TFT Sensor DTCs P0711, P0712 or P0713. |
| • | No TCC Sol. Valve DTC P0740. |
| • | No TCC Stuck ON DTC P0742. |
| • | No 1-2 SS Valve DTC P0753. |
| • | No 2-3 SS Valve DTC P0758. |
| • | No 3-2 SS Valve Assy. DTC P0785. |
| • | No TFP Val. Position Sw. DTC P1810. |
| • | No TCC PWM Sol. Valve DTC P1860. |
| • | The vehicle speed is greater than 8 km/h (5 mph). |
| • | The engine vacuum is 0-105 kPa. |
| • | The engine torque is 5-450 lb ft. |
| • | The engine speed is greater than 450 RPM for 5 seconds. |
| • | The transmission fluid temperature is 20-130°C (68-266°F). |
| • | All of the above conditions are met three times and the combination
of Conditions 1 and 2 or Conditions 2 and 3 occurs three times. |
Condition 1
| • | The TP angle is greater than 15%. |
| • | First gear is commanded for 2 seconds. |
| • | The speed ratio is 0.5 to 3.0 (speed ratio is the engine speed
divided by the output speed). |
| • | The transmission output speed is 400-1500 RPM. |
| • | The TCC slip speed is -100 to -3000 RPM for
1 second. |
Condition 2
| • | The TP angle is 13-50%. |
| • | The TP angle is within +/- 7%. |
| • | Third gear is commanded for 2 to 5 seconds. |
| • | The speed ratio in 3rd gear does not drop more than 0.3 from the
last speed ratio in 2nd gear. |
| • | The TCC slip speed in 3rd gear remains 300 RPM higher than
the last TCC slip speed in 2nd gear. |
| • | All conditions met for 1.5 seconds. |
Condition 3
| • | The TP angle is greater than 13%. |
| • | Fourth gear is commanded for 1 second. |
| • | The speed ratio is 2.05 to 8.0. |
| • | The transmission output speed is 1400-2500 RPM. |
| • | The TCC slip speed is 1000-4000 RPM for 1 second. |
Action Taken When the DTC Sets
| • | The VCM illuminates the Malfunction Indicator Lamp (MIL). |
| • | The VCM commands third gear only. |
| • | The VCM inhibits TCC engagement. |
| • | The VCM commands maximum line pressure. |
| • | The VCM freezes shift adapts from being updated. |
| • | DTC P0756 stores in VCM history. |
Conditions for Clearing the MIL/DTC
| • | The VCM turns OFF the MIL after three consecutive trips without
a failure reported. |
| • | A scan tool can clear the DTC from the VCM history. The VCM clears
the DTC from the VCM history if the vehicle completes 40 warm-up cycles without
a failure reported. |
| • | The VCM cancels the DTC default actions when the fault no longer
exists and the ignition is OFF long enough in order to power down the VCM. |
Diagnostic Aids
| • | Verify that the transmission meets the specifications in the 4L60-E
Shift Speed
table. |
| • | Other internal transmission failures may cause more than one shift
to occur. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step verifies that the scan tool commanded all shifts, that all
shift solenoids responded correctly, but all the shifts did not occur.
DTC P0756 2-3 Shift Solenoid Valve -- Performance
Step
| Action
| Value(s)
| Yes
| No
|
1
| Was the Powertrain On-Board Diagnostic (OBD) System Check
performed?
| --
|
Go to Step
2
| Go to
Powertrain On Board Diagnostic (OBD) System Check
(4.3L) or
Powertrain On Board Diagnostic (OBD) System Check
(5.0L and 5.7L) in Engine Controls
|
2
|
- Install the Scan Tool
.
- With the engine OFF, turn the ignition switch to the RUN position.
Important: Before clearing the DTC(s), use the scan tool in order to record the
Freeze Frame and Failure Records for reference. Using the Clear Info function
will erase the stored Freeze Frame and Failure Records from the VCM.
- Record the DTC Freeze Frame and Failure Records, then clear the DTC(s).
- Drive the vehicle in D4 range under the following conditions:
Accelerate the vehicle, ensuring that the VCM commands 1st, 2nd, 3rd
and 4th gears.
Did you detect a 1-2-2-1 or 4-3-3-4 shift pattern?
| --
|
Go to Step 3
| Go to
Diagnostic Aids
|
3
| Check the shift solenoid/hydraulic
circuit for the following conditions:
| • | An internal malfunction |
| • | Damaged seals on the shift solenoid valves. |
Did you find and correct the condition?
| --
|
Go to Step 4
| --
|
4
| In order to verify your repair, perform the following procedure:
- Select DTC.
- Select Clear Info.
- Drive the vehicle in D4 under the following conditions (only if
traffic and road conditions permit):
| • | Hold the throttle at 50% and accelerate to 64 km/h (40 mph). |
| • | Stop the vehicle, engine idling. |
| • | Hold the throttle at 25% and accelerate to 80 km/h (50 mph). |
- Select Specific DTC. Enter DTC P0756.
Has the test run and passed?
| --
| System OK
|
Begin the diagnosis again. Go to Step 1
|
