2012 silverado 6 speed transmission problems

Chevrolet transmission problems can be caused by something as simple as low transmission fluid, a dirty filter, or even a dead battery. They can also be caused by more serious issues such as internal hydraulic leaks, faulty valve bodies, failed clutch packs, torque converters, and other problems requiring a complete transmission overhaul or replacement.

Symptoms

The first sign that you may have a possible transmission problem could be the check engine light coming on.

If these symptoms are ignored, your Chevrolet may get stuck in limp mode and not shift at all.

Here is a quick overview of Chevy transmission problems and possible causes.

• Chevy transmission slipping or no reverse – Reverse clutches may be worn out, have a fluid leak, or have a broken sun shell.
• Won’t shift to higher gear until you let off the gas – Faulty throttle position sensor. A leak in the servo assembly or accumulator. Low transmission fluid level.
• Chevy transmission won’t shift, stuck in 1st gear or limp mode – Speedometer may display zero at all times. It could be internal transmission failure, low transmission fluid, or a faulty Vehicle Speed Sensor (VSS sensor).
• Chevy transmission won’t go into 3rd or 4th gear – This indicates that 3 or 4 gear clutches are worn.
• Transmission grinding noise – sun shells (planetary gears) may be damaged.
• Chevy will drive in 1st, and 3rd only but not 2nd or 4th gear – Sunshell may be damaged, or splines are sheared off, servo seals may be worked out, and bands themselves could be worn out.
• Transmission shifts harshly, and Chevy feels sluggish when accelerating – Check engine light may also turn on. First, read the fault codes with a transmission scanner. Then check the transmission fluid level.
• Transmission is stuck in limp-home mode – Possible causes include low voltage or communication problems with transmission and engine control units. The issue can be faulty shift solenoid, low transmission fluid level, wiring problems, TCM, ECU, PCM software issues, TCC solenoid failure, TCC clutch worn out, bad TCC (Torque Converter Clutch) lockup, or faulty brake pedal switch. The throttle position sensor may no longer send the correct electrical signal.
• Chevrolet transmission shifts harsh on P or N  – Electronic Pressure Control (EPC) solenoid may have failed. Get it diagnosed and repaired by a mechanic as soon as possible to avoid further transmission damage.
• Chevy doesn’t move – When you put your Chevy car or truck in Drive or reverse, it may not move. Common problems include no transmission fluid and failed transmission fluid pump.

The first steps in troubleshooting the Chevrolet transmission problem are to read the fault codes from the Transmission Control Module (TCM) and check the transmission fluid level. These steps can be completed by the owner, a Chevrolet dealer, or an auto mechanic. In the meantime, avoid driving your Chevy, or you may cause further damage to the automatic transmission.

Read Fault Codes

Reading Chevy transmission codes from the PCM/TCM module requires more than a simple OBD-II scanner.

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It requires a diagnostic scanner that will retrieve fault codes from PCM, such as Foxwell Chevy Transmission Scanner, Launch Transmission ABS Diagnostic Tool, and Autel Transmission Scanner.

1. Locate the diagnostic port under the dashboard (driver’s side) and plug in your scanner.
   
2. Turn on the ignition and your scanner. 
   
3. Select Chevy from the main menu, then select your model. 
   
4. Select Control Units, then select Automatic Transmission.
   
5. Select Read Fault Codes.

All codes that show as CURRENT should be fixed. It is possible to clear the codes at this stage, but it is not recommended without first fixing the underlying problem. This may allow you to get the vehicle out of limp mode temporarily. Once the car is driven and the codes return, your Chevy will get stuck in limp mode again.

If many fault codes are displayed as stored, they could be caused by a dead battery. The problem could be the Powertrain Control Module (PCM / TCM) if you see several current fault codes.

First, you need to check the fuses. If fuses are good, inspect wire harnesses to rule out any shorts and check the harness connector at the transmission housing.

Most scanners will allow you to view PCM hardware and software versions. Get the software information and call the dealer to ask if there are any software updates for the PCM.

Pay attention to the codes and, most importantly, any fault code with a CURRENT status. You will get a description for each code, but further research into each code may be required to understand the problem better.

Knowing which transmission is installed in your Chevy is important to learn about problems that affect that particular transmission. Use our VIN decoder to look up Chevy Transmission by VIN.

Check Transmission Fluid Level

Low transmission fluid causes most Chevy transmission problems, including harsh shifting, delayed shifting, and no shifting if there is a total loss of transmission fluid.

If your Chevy transmission is low or out of fluid, avoid running or driving until the transmission fluid level is corrected to avoid unnecessary transmission damage.

How to Check Chevy Transmission Fluid

1. Park your Chevy on level ground. Set the parking brakes.
2. Open the hood. Pull the hood release and open the hood.
3. Remove the transmission dipstick. With the engine running and in Park, remove the transmission dipstick. Please do not confuse it with the engine oil dipstick. Some models do not have a transmission dipstick and need to check by removing the oil fill plug found on the side of the transmission housing.
4. Clean dipstick. Wipe the dipstick with a lint-free clean cloth and reinsert it.
5. Reinsert the dipstick and remove it. Remove the transmission dipstick and read the transmission fluid level. It needs to be between the MIN and MAX for the cold range. If there is no cold range in the dipstick, it is important to indicate transmission fluid on the dipstick. Transmission fluid should be pink in color and almost clear. If the transmission fluid looks burnt, dark, or has metal shavings, have an auto mechanic diagnose and, if necessary, change the transmission fluid.
6. Drive the vehicle for 15 minutes. This will allow the transmission fluid to warm up.
7. Recheck the transmission fluid level. Recheck the transmission fluid level to ensure the level is correct.
8. If transmission fluid level is below the min mark, add only the recommended Chevy transmission fluid noted in your owner’s manual. Do not overfill past the MAX / HIGH mark.

Also, check if any recalls exist for your Chevrolet that could affect the transition. You can check Chevy recalls by calling any local Chevy dealer or check for recalls online.

Check Trans Pump Operation

A failed Chevy transmission fluid pump will cause your car not to move or barely move when placed in Drive.  You can perform a simple test to check the transmission fluid level with the engine on and off. First, check the transmission fluid level with the engine off.

Next, start the engine and run the shifter through all the gears PRND while parked. Move back to Park and recheck the transmission fluid level.

• Transmission Fluid Level Changes – If the level has gone down when the engine runs, the pump is working.
• Transmission Fluid Level Does Not Change – The pump is faulty if the transmission fluid level does not go down when the engine is running.

Reading transmission fault codes and checking the transmission fluid level should always be performed as soon as a Chevy transmission shows shifting problems. If you cannot perform these procedures yourself, see an auto mechanic dealer, or visit an automatic transmission repair shop.

Do not use a transmission fix additive without getting your Chevy transmission diagnosed by a professional first. Only use a transmission additive such as Lucas Transmission Fix as a last resort. Your Chevy transmission will most likely need to be removed, rebuilt, or replaced.

Common Problems

The transmission stays in gear for too long.

Many older Chevrolets with automatic transmissions can suffer from incorrect gear shifting. This will show up as delayed, harsh gear changes or, in some cases, lack downshifts when trying to accelerate.

This problem can be intermittent, and sometimes it may trigger a check engine light.

Possible Causes

• Faulty throttle position sensor, which in most cases will trigger a check engine light and corresponding fault. The throttle position sensor can be monitored using an OBD-II diagnostic tool.
• Inside the valve body is a Torque Converter Clutch (TCC) regulator valve. It can become worn out with time and cause harsh shifting from 1st to 2nd gear. This will trigger a P1870 code. Various rebuild kits can solve this issue.
• Shift solenoids may be faulty or clogged. If the fault is electrical, it may trigger a check engine light. Mechanical issues and clogged solenoids will rarely result in a check engine light.

Missing higher gears or transmission stuck in 1st gear.

Chevrolet cars with 4L60E or 4L65E transmissions can experience sporadic or constant issues with gear selection. In some cases, this will show up as refusing to shift from 2nd to 3rd gear. In other cases, the transmission will stay in 1st gear only and will not engage reverse either.

Possible Causes

• Worn clutch pack for 3rd and 4th gear, which disables 3rd gear engagement. This happens as a result of a leaking piston that engages the clutch. Replacing the clutch pack and corresponding piston solves the problem.
• The drive shell’s collar can break off, leaving the transmission in 1st gear only, with no 2nd gear or reverse available. Sometimes, the collar splines can wear out, which can cause the same issues. Replacing the drive shell is the only solution.

Missing reverse gear

Chevrolet cars with 4L60E or 4L65E transmission can experience sporadic or constant reverse loss. When this happens, the car will not reverse, while there will be no issues with other gears.

Possible Causes

• These transmissions use a servo that engages the reverse gear. If it fails, the transmission will not engage in reverse. It is easy to replace, but the oil pan and valve body must be removed.

Incorrect gear shifts, gear slipping, or overheating.

Newer Chevrolet cars with a 6-speed 6L80 transmission can experience sporadic or constant transmission issues. This ranges from harsh or slow shifting, failure to engage gears, or gear slipping. In some cases, it may even cause transmission overheating.

Possible causes

These 6-speed transmissions rely on correct hydraulic pressure for proper operation. This is ensured by a pressure regulator system, which uses springs and valves. With time, various components wear out and cause a pressure drop. Rebuilding or replacing the pressure regulator system solves the problem.

Shaking and shuddering when changing gears

Many Chevrolet cars with 8-speed 8L90 and 8L45 transmissions suffer from an issue known as ‘Chevy shudder.’ Several symptoms may occur during gear shifts, including shaking, juddering, and harsh shifting. In some cases, there even might be a noticeable clunk. This issue affects all gears, although more noticeable in 1st and 2nd gear.

Possible causes

• This well-known issue affects all GM vehicles with this 8-speed transmission, leading to a class-action lawsuit. According to the Technical Service Bulletin (TSB 18-NA-355), flushing factory-used transmission fluid and swapping it for Mobil 1 Synthetic LV ATF HP fluid may improve the situation.
• If there is no noticeable improvement after transmission fluid flush, the torque converter could be glazed, especially if it has been used with this issue for a long time. Replacing the torque converter will solve the issue.

Improbable transmission temperature

Chevrolet cars with 8-speed automatic transmissions suffer from issues related to transmission temperature. This can range from simple symptoms such as temperature readings that make no sense to more serious transmission overheating, slipping, and harsh shifting. This problem is accompanied by a check engine light and a corresponding DTC code.

Possible causes

• These transmissions have a high rate of failure for transmission fluid temperature sensors. This triggers a P0711 code. Check the wiring, connector, and sensor itself. Replace or repair what is needed.
• A low transmission fluid level or a dirty filter can cause overheating, leading to other issues with transmission operation.

FAQ

The transmission seal or pump bushing may be damaged. To replace it, a transmission has to be removed from the vehicle.

The problem can be a defective valve body, faulty PCM, wiring issue, faulty vehicle speed sensor, or defective throttle position sensor.

The problem can be low transmission fluid, bad shift solenoid, wiring problem, or PCM issue. It may also be a bad throttle position sensor and even a clogged catalytic converter.

Problems can be low transmission fluid if what you hear sounds like a whine. Grinding noise could be due to worn planetary gear. May require transmission to be removed and rebuilt.

Additional Resources

1. How to read Chevy Transmission Codes – YOUCANIC
2. Best Diagnostic Scanner for Chevrolet – YOUCANIC
3. TSB Seems To Fix 8-Speed Automatic GM Transmission Problems – GM Authority
4. GM faces a possible class-action lawsuit over 8-speed transmission – Auto Blog.

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We hope you find the Troubleshooting Chevrolet Transmission Problems guide helpful. Check these troubleshooting and repair guides for more help on your Chevrolet.