D4 light does not engage?

SDYLAN

MEMBER
1991 ACURA LEGEND
3.2L
V6
2WD
AUTOMATIC
120,000 MILES

I was having a problem with my fuel pump relay, the main one. I then replaced it but now my D4 light won’t come on. I get d1d2d3 But I do not get d4. I was reading up a little bit and it says it may be the transmission control unit, but I can’t find out where it is as anybody else had this issue.

Tuesday, April 22nd, 2025 AT 5:38 PM

1 Reply

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Hi,

Does the transmission shift normally when placed in D4? I ask because there are individual bulbs that can fail. See pics below.

Next, as far as the transmission control module, the vehicle's transmission is controlled by the engine control module. There isn't a separate module only for the transmission. With that, I would recommend checking for diagnostic trouble codes. Here is a link that explains how to retrieve them.

https://www.2carpros.com/articles/honda-car-1990-1995-obd1-code-retrieval-procedure-and-definition-table

Try that and let us know if you find any codes and what they are.

Let us know,

Take care,

Joe

See pics below.

Images (Click to make bigger)