I just changed out my tcu you. Fixed the problem with my trans not shifting on its own. But now the d4 light does not come on at all. It work because i see it come on when I turn the car on. This is one of those annoying things that i just got to fix.

Pls tell us what year your car is. There are different answers for different years and models. So help us to help you.

Pls tell us what year your car is. There are different answers for different years and models. So help us to help you.

I got a 92 accord ex.

The shfter position lights are powered by the dash dimmlight is grounded through the shifter position switch. So if the other lights work then check the contact on the shifter positon switch. Remove the center console and the switch is a white module on the left side near the shifter. It can be disassembled in position and the contacts cleaned. This is the first time I have heard of a D4 light out. Most of the time it is a P contact dirty. Clean all of the contacts while you are at it.

What's the 'preferred' contact cleaner? Something from Radio Shack or good old denatured alcohol?

They use an anti-corrosive grease on the contacts. So a petroleum solvent will remove the gease, then use a emery paper to remove the film then recoat with something like DeOx. Before you clean the contacts, you can short the terminal that goes to the D4 light to ground and the D4 should light.