
The accumulator system is one of the systems used for controlling and influencing the 1-2 and 3-4 shift. This occurs when the ECM EPC solenoid driver has failed especially on the 1993-1997 models. Far too often the PID will display the proper commanded amperage when in fact it is wrong. It is not advisable to rely on the EPC solenoid commanded amperage PID on the scan tool. Diagnosing line pressure problems on a 4L60E requires a pressure gauge and DVOM to measure the commanded EPC solenoid amperage. Once the TCC slippage problems have been addressed the other line pressure areas of concern are the ECM EPC solenoid driver failure, lean misfire conditions, MAF sensor problems and the EPC solenoid itself. Many of the harsh 1-2 problems are due to the TCC slippage complaints setting P1870-P0894 codes and putting the transmission into high line pressure mode. Line pressure boost control has been the Achilles heel of the 4L60E for a long time.
