Diagnostic Port for 91-93 3000GT and Stealth

Many people come to us with problems asking for our help, when the solution is right in front of their face. How do I read my check engine light codes, SRS codes, ABS codes, etc? Well, it’s as simple as having a multimeter or voltmeter. Analog voltmeters are the easiest to read, but you can certainly read it using a digital meter as well. They can be picked up for $10-100. You will also want some wire, and either really small female spade connectors or alligator clips. I personally like to use alligator clips myself.

Reading the engine codes is super easy. Here is a picture of the diagnostic port and the pin numbers on that port. This port is located next to the fuse box inside the car on the driver side.


*photo courtesy of Stealth316.com*

For the engine codes, you will place the positive voltmeter probe on pin 1 and the negative on pin 12. This will make the voltmeter sweep long and short pulses. Count the long pulses and that will be the tens digit of the code. The short pulses following will be the ones digit of the code. If you get 2 long pulses and 5 short pulses, then you have code 25. Keep the meter connected to check for more codes. It will keep repeating the code sequence over and over again. If there are no codes, it will just do short pulses constantly. If you have a bad ECU, it can not pulse at all (no communication with the ECU).

Now, here is a chart showing what all of the pins mean. This will come in handy to diagnose just about anything on the car.

1991-1993 Self-Diagnosis Check Connector
Pin Function
1 ECM – MPI functions
2 unused
3 ECS control unit
4 ABS control unit
5 Auto-Cruise control unit
6 ELC-4 A/T control unit or unused
7 Air Conditioner control unit
8 SRS diagnosis unit
9 ETACS unit
10 Query – ECS, ABS, ECM, A/T, AC
11 Speed sensor
12 Ground


To test for error codes for any of those above units, just do the same thing as you did for the engine codes. Negative to pin 12 and positive to whichever pin correlates to the appropriate control module you are trying to access. Doing it this way will make diagnosing problems with your car so much easier and more reliable! In another article, we will discuss the codes and what they mean.