GM shift DTC
This TSB applies to 2007 and prior GM passenger cars and light duty trucks, 2003-2007 Hummer H2, 2006-2007 Hummer H3, and 2005-2007 Saab 9-7X, equipped with 4L60-E, 4L65-E or 4L70-E automatic transmissions.
Some dealership technicians may have difficulty diagnosing DTC P0756 (2-3 shift valve performance) on 4L60-E, 4L65-E or 4L70-E automatic transmissions. As detailed in the service manual, when the PCM detects a 4-3-3-4 shift pattern, DTC P0756 will set.
Some customers may also describe a condition of a second, third or fourth gear start that may have the same causes but has not set this DTC yet. Below are some tips when diagnosing this DTC:
- This is a performance code. This means that a mechanical malfunction exists.
- This code is not set by electrical issues such as a damaged wiring harness or poor electrical connections. Electrical problems would cause a DTC P0758, P0787 or P0788 to set.
- The most likely cause is chips/debris plugging the filtered AFL oil at orifice #29 on the top of the spacer plate (48). This is a very small hole and is easily plugged by a small amount of debris. It is important to remove the spacer plate and inspect orifice #29 and the immediate area for the presence of chips/debris. Also, the transmission case passage directly above this orifice and the valve body passage directly below should be inspected and cleaned of any debris.
- This code could be set if the 2-3 shift valve (368) was stuck or hung-up in its bore. Inspect the 2-3 shift valve and the 2-3 shuttle valve (369) for free movement or damage and clean the valves, the bore and the valve body passages.
- This code could be set by a 2-3 shift solenoid (367b) if it was cracked, broken or leaking. Refer to Shift Solenoid Leak test in the appropriate service manual for the leak test procedure. Based on parts return findings, a damaged or leaking shift solenoid is the least likely cause of this condition. Simply replacing a shift solenoid will not correct this condition unless the solenoid has been found to be cracked, broken or leaking.