Connect a jumper wire between terminals TE1 and E1 terminals and by turning the key on, it will start flashing the codes in your dash. On Tercel and MR2, use the jumper wire between terminals T and E1 instead.

If there are no codes, the check engine light will flash 2 times per second CONSTANTLY with no patterns or pauses. If there are any codes, it will be shown in 2 digits codes. Example: code 24 is shown as 2 flashes, a pause followed by 4 flashes. If there are mode codes, the next one will transmitted after 2.5 seconds. (One some models, codes are displayed in one digit code only and the difference is the codes are displayed with 4.5 seconds delay between codes). When finished reading the codes, turn the key off and remove the jumper wire.

Shown above is an example of the location of the diagnostic connector.

Here are the common codes for Toyota vehicles 1988-95:

Code 11 Momentary interruption in power supply to ECU (electronic control unit or computer) up to 1991
Code 12 Engine revolution signal missing
Code 13 Rpm signal to ecu missing above 1000 rpm
Code 14 Igniter signal to ecu missing
Code 16 A/T control signal missing from ecu
Code 21 Main oxygen sensor signal fault
Code 22 Water temperature sensor circuit fault
Code 23 and 24 Intake air temperature signal fault
Code 25 Air/fuel ratio LEAN
Code 26 Air/fuel ratio RICH
Code 27 Sub-oxygen sensor signal or heater circuit fault
Code 28 No.2 oxygen sensor/heater signal fault
Code 31 and 32 Air flow meter circuit or Vacuum sensor signal fault
Code 34 and 36 Turbo-charging pressure signal fault
Code 35 Altitude compensation sensor signal fault
Code 41 Throttle position circuit fault
Code 42 Vehicle speed sensor circuit
Code 43 No starter signal to the ecu
Code 51 AC signal on; DL contact off (in trany shifter with diagnostic connector jumped)
Code 52, 53 and 55 Knock sensor fault
Code 71 EGR system malfunction
Code 72 Fuel cut solenoid signal fault
Code 78 Fuel pump control signal fault
Code 81, 83, 84 and 85 TCM communication fault

After getting the above OBD1 fault codes, reset it by disconnecting the
battery negative terminal for 1-2 minutes and reconnect. Get the code again
when the engine is warmed up. The next bunch of codes are the ones you will fix.

Knowing this Toyota 1983-1985 OBD1 Decoder along with the knowledge of common
vehicle fixes for your Toyota model will help you fixed the problem quick.

When you buy the suspected defective Toyota parts, the dealer can usually tell the
common fixes. Another way some Toyota get hold of the common fixes is by getting a
repair estimate from a garage. If the total repair cost is reasonable, go ahead and
tell them to fix it. Otherwise, if the defective part is quoted in the estimate is expensive,
you can tow the vehicle home and do it yourself especially if the labor cost
is around $100 an hour and they cannot give you the exact labor time estimate.

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Automotive Troubleshooting Secrets