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Dave Nova
Dave Nova, GMC Technician
Category: GM
Satisfied Customers: 19452
Experience:  ASE Master Certification. GM World Class Certification
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2006 GMC: 6.0...trany..higher it shifts hard like it has a shift kit

Customer Question

I have a 2006 GMC 2500hd with a 6.0. When the transmission is cold it shifts great but when the trany gets up to around 110 degrees or higher it shifts hard like it has a shift kit. i had the trany filter changed and it still does it
Submitted: 6 years ago.
Category: GM
Expert:  Dave Nova replied 6 years ago.

Hello and thank you for using JustAnswer. My name is XXXXX XXXXX I will do my best to help you with your GMC problem.


Is the check engine light on while driving?

Customer: replied 6 years ago.
yes it is
Expert:  Dave Nova replied 6 years ago.
The hard shifting and the check engine light being on both point to an electrical problem. This will likely be a faulty sensor or a pressure control solenoid within the transmission. The best place to start is to have the computer scanned for trouble codes. You can have the codes scanned for free at Autozone. If you need additional help with diagnosis after you get the codes, please let me know.
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Customer: replied 6 years ago.
i had a romote starter put in lastweek and its done it ever since. the shop checked every connection and said everything was right and it still did it so i unpluged the module and tried it and once again it still did it i just want to make sure it doesnt have to do with that
Expert:  Dave Nova replied 6 years ago.

Even if the remote start is the source of the problem, the trouble codes will still be in the computer for 40 drive cycles or until the codes are cleared with a scan tool. If you can get the codes scanned and then cleared this may alleviate the problem. Record what number the trouble code is and let me know if you need additional help.

Customer: replied 6 years ago.
hey Dave there was no recent code in the system. there was an old code CO894 component slip. They took the pan off and inspected the tcc soleniod because of a bulletin 08-07-30-008B but the soleniod wasn't cracked. is there anything else i should look for?
Expert:  Dave Nova replied 6 years ago.

I believe the problem is in the torque converter clutch system. When there is slippage, the P0894 code will set.


Action Taken When the P0894 DTC Sets

  • For California emission equipped vehicles, the PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. For Federal emission equipped vehicles, the MIL is not illuminated.
  • The PCM commands maximum line pressure. This is what causes the harsh shifts.
  • The PCM inhibits the TCC engagement.
  • The PCM freezes transmission adaptive functions.
  • The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame, California only, and Failure Records, California and Federal.
  • The PCM stores the DTC P0894 in PCM history during the second consecutive trip, California, or the first trip, Federal, in which the Conditions for Setting the DTC are met.

Below is a list of potential problems that can cause the P0894 code.


  • A TFP manual valve position switch malfunction can set DTC P0894.
  • A mechanical failure of the shift solenoids or TCC PWM solenoid valve can set DTC P0894.
  • Internal transmission failures can result in a DTC P0894.
  • Sticking or contaminated shift valves may cause intermittent slipping in D4.
  • DTC P0894 defaults to an elevated line pressure condition which may result in partial TCC apply. This may produce an idle surge that could stall the engine.