Transmission Issue

motox915 · December 31, 2011

Ok so this is going to be a little lengthy, my appologies. I have never had any issues with my 1999 Silverado 1500 5.3 V8 but i added Lucas Oil stop slip to my tranny for preventative maintanence, then 3 days later my tranny started slipping, checked fluid level and it was over filled so i had fluid sucked out until it was at the hash marks when hot in park. The truck is still not working properly. From a dead stop it shifts like normal at about 15mph however it will not shift after that. Same if I try to shift manually, shifts fine from 1-2 but when i move the gear shifter from 2-3 nothing happens. I can still accelerate up to about 55mph in 2nd but when i let off and go back to try to accelerate the RPM's climb to about 2500 or 3000 depending on speed before the transmission engages again and i can accelerate again. Last normally i can cruise at 45 around 1600 RPMs but now to cruise at 45 I have to hold it around 2800 RPMs. Any ideas or help would be greatly appreciated! I am still in high school and had to save for 18 months to get this truck so I am hoping i can get it fixed without a new tranny!

GMstrong · December 31, 2011

overfilling the trans fluid is the same as low fluid.Trans is done look for a new one or rebuild.You added the lucas because it was slipping before?or did you add the lucas then it started slipping?

travis73 · December 31, 2011

I would take it to a transmission place and have them change the fluid and filter,the additive may have done more damage than good,sounds like the tranny is gone though.good luck

markw8 · December 31, 2011

Almost no chance the Lucas caused this. Have it diagnosed at a good shop. It probably is done though.

Mark

motox915 · December 31, 2011

Thank you for all the info, it has never slipped before, I just added the lucas for preventative then 3 days later this started. I have been reading around forums and have noticed a lot of things about a Solenoid B that is the 2-3 solenoid so is there any chance that is what is wrong because it won't shift from 2-3?

motox915 · December 31, 2011

Just an update i just went and had the codes read and got the code P0756 back which is Shift Solenoid B. And i have seen that this is the 2-3 shift solenoid. Does anyone know how to fix this and whether the solenoid is internal or external.

txab · December 31, 2011

Internal

gmtech4 · January 1, 2012

its not that simple pal,but ,dont listen to me ,and ..Travis ,,,oil and filter DOES NOT fix transmission concerns,,

like said ,GET IT DIAGNOSED AT AT GD TRANNY SHOP OR DEALER THAT HAS A TRANSMISSION SPECIALIST

spend money wisely bud

there is this diag for the code and a bulletin,

Document ID: 367853

DTC P0756 2-3 Shift Solenoid Valve Performance (4.8L and 5.3L)

Table 1:DTC P0756 2-3 SS Valve Performance (4.8L and 5.3L)

Thumbnail, DTC P0751, P0756

Circuit Description

The 2-3 shift solenoid (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 SS valve, the 2-3 SS valve allows four different shifting combinations.

When the PCM 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 Running the DTC

• No MAF sensor DTCs P0101, P0102 or P0103.

• No TP sensor DTCs P0122 or P0123.

• No VSS assembly DTCs P0502 or P0503.

• No TFT sensor DTCs P0711, P0712 or P0713.

• No TCC solenoid 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 assembly DTC?P0785.

• No TFP manual valve position switch DTC?P1810.

• No TCC?PWM solenoid valve DTC?P1860.

• The vehicle speed is greater than 8?km/h (5?mph).

• The gear range is D4.

• The TP angle is 15–50%.

• The TP angle is constant within +/-?7%.

• The PCM commands a 1-2, 2-3 and 3-4 shift.

• The engine vacuum is 0–105?kPa.

• The engine torque is 5–450?lb?ft.

• The engine speed is greater than 300?RPM for 5?seconds.

• The engine is not in fuel cutoff.

• The transmission fluid temperature is 20–130°C (68–266°F).

Conditions for Setting the DTC

DTC?P0756 sets if the following conditions occur three times:

• 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 (speed ratio is engine speed divided by transmission output speed).

• The TCC slip speed in 3rd gear remains 300?RPM higher than the last TCC slip speed in 2nd gear.

All of the above conditions are met for 1.5?seconds and one of the following conditions occurs:

Condition 1

• First gear is commanded for 2?seconds.

• The transmission output speed is 400–1500?RPM.

• The speed ratio is 0.5 to 3.0.

• The TCC slip speed is ?3000 to ?100?RPM for 1?second.

Condition 2

• Fourth gear is commanded for 1?second.

• The transmission output speed is 1400–2500?RPM.

• The speed ratio is 2.05 to 8.

• The TCC slip speed is 1000 to 4000?RPM for 1?second.

Action Taken When the DTC Sets

• The PCM illuminates the malfunction indicator lamp (MIL).

• The PCM commands third gear only.

• The PCM inhibits TCC engagement.

• The PCM commands maximum line pressure.

• The PCM freezes shift adapts from being updated.

• The PCM stores DTC?P0756 in PCM history.

Conditions for Clearing the MIL/DTC

• The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.

• A scan tool clears the DTC from PCM history.

• The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.

• The PCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids

• Verify that the transmission meets the specifications in the

Shift Speed table.

• Other internal transmission failures may cause more than one shift to occur.

• Refer to the

Shift Solenoid Valve State and Gear Ratio table.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

2 This step verifies that the PCM commanded all shifts, that all shift solenoids responded correctly, but all the shifts did not occur.

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 in Engine Controls

<a href="http://gsi.xw.gm.com/newsi/showDoc.do?docSyskey=367853&cellId=6956&pubObjSyskey=4377628&from=sm&pubCellSyskey=2112115&deliveryEffectiveDate=Dec+1%2C+2011#td02">2

1. Install the Scan Tool .

2. With the engine OFF, turn the ignition switch to the RUN position.

3.

Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM. Record the DTC Freeze Frame and Failure Records.

4. Clear the DTC.

5. Drive the vehicle in D4 range, under the following conditions: Accelerate the vehicle, ensuring that the PCM 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

Inspect the shift solenoid/hydraulic circuit for the following conditions:

• An internal malfunction

• Damaged seals on the shift solenoid valves. Refer to Shift Solenoid Leak Test.

Did you find and correct the condition?

—

Go to Step 4

—

4

Perform the following procedure in order to verify the repair:

1. Select DTC.

2. Select Clear Info.

3. 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).

• 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).

4. Select Specific DTC.

5. Enter DTC?P0756.

Has the test run and passed?

—

System OK

Go to Step 1