On the right side, below the glove box there is a cover. Remove it and locate the service check connector. This is a small plug with two terminals. Connecting the two terminals with a short piece of wire will cause the D4 light to blink a code that corresponds to the fault.
The D4 indicator light indicates a failure code by blinking frequency. This can
indicate any number of simultaneous component problems by blinking separate
codes, one after another. Problem codes 1 through 9 are indicated by individual
short blinks. Problem codes 10 through 15 are indicated by a series of long and
short blinks. One long blink equals 10 short blinks. The number of long blinks
equals the first digit, the number of short blinks equals the second digit.