This was taken from G2IC.com I was under the assumption your car is 91GS ?
Depending on which year your Teg is, there are two different ways to check your ECU code.
1990 and 1991 Tegs:
Your ECU is located under the carpet on the passenger side of the car. You have to pull back on the carpet to expose the ECU which is brass in color. There is a circular window on the face of it with red LED in it. This LED will blink and this is where you read your code.
To get the LED to blink, you must turn the car to the "ON" position but do not start it. The LED will blink with fast blinks and with slow blinks. If you have four fast and two slow, that is code 42.
1992 and 1993 Tegs:
Your ECU is located in the same spot as 90-91's but you won't be reading the code off the ECU. For you, you must jump a connector and then your Check Engine light will blink to tell you the code.
The connector you must jump is located under the glove box and should be green in color. How to jump -- Helms: Chapter 11 page 40
0 - ECU
1 - Oxygen Sensor
3 - MAP Sensor
5 - MAP Sensor
6 - Crank Angle
7 - Throttle Angle
8 - TDC Position
9 - No. 1 Cylinder Position
10 - Intake Air Temperature
12 - Exhaust Gas Recirculation (EGR) System
13 - Atmosphere Pressure
14 - Electronic Air Control
15 - Ignition Output Signal
16 - Fuel Injector
17 - Vehicle Speed Sensor
20 - Electronic Load Detector
22 - VTEC System Malfunction
23 - Knock Sensor
41 - O2 Sensor
43 - Fuel Supply System
45 - System Too Rich or Too Lean
48 - Primarry Heated O2 Sensor
54 - Crankshaft Speed Fluctuation Sensor
61 - Primary O2 Sensor Circuit
63 - Secondary O2 Sensor Circuit
67 - Catalyst System
70 - Automatic Transaxle
71-74 - Random Misfire
80 - Exhaust Gas Recirculation
86 - Engine Coolant Temperature Circuit
90 - Evaporative Emission Control System Leak Detected
91 - Fuel Tank Pressure Circuit
92 - Evaporative Emission Control System Insufficient
NOTE: Some trouble codes are not listed for certain models and some codes only apply to California cars.