I changed the trans fluid in a customers 99 Honda Accord today and the d4 light started blinking. I actually did a trans. flush with the machine. What this does is the old fluid is pumped through the machine using the cars pump in the trans and I control the outflow with a valve. At the same time the machine pumps new fluid in which is controled by another valve. You do this until the fluid is clean. Well we did this and the light came on. The car will not downshift into first gear. I can manually shift the car and it works fine . I went to another shop to check the codes and erase the memory. As soon as we erased the light would go off and then come right back on. Idont understand why replacing dirty fluid with new fluid would cause this.
Help . Please help.
Thanks.
Neil