I think this can be useful since some of us don't know how to obtain OBD1 codes.

To get the codes yourself, turn the engine off and connect a jumper wire (Or a paper clip works too) between terminals TE1 and E1 of the diagnostic terminal connector located in the engine compartment or under the left side of the dash.

When you turn the key on (do not start engine), the check engine light lamp in your dash panel will start to flash the codes. Codes are usually shown in 2 digits numbers like code 24 is 2 flashes, a pause and 4 flashes. A pause of 2.5 seconds will follow the next code. When all codes are transmitted, the entire code will be flashed again after 4.5 seconds.

Clearing the codes is simple that is done by removing the fuse of the EFI from junction box 2 for 10 seconds. Make sure to remove the jumper wire and switch the key off before clearing the codes.

Here are some common Lexus vehicles 1990-1995 codes:

Code 12 and Code 13 Rpm signal circuit fault
Code 14 Igniter signal circuit fault
Code 16 ECT control signal fault
Code 21 and Code 28 Main oxygen sensor fault (for ES300; SC300 & GS300 models)
Code 22 Coolant temperature circuit fault
Code 24 Intake temperature sensor circuit fault
Code 25 and Code 26 Air fuel ratio fault (for ES300 & SC300 models)
Code 27 Sub-oxygen sensor circuit fault (for ES300 CA & GS300 models)
Code 31 Low airflow meter voltage (for ES300 and GS300 models)
Code 32 High airflow meter voltage (for ES300 model)
Code 35 Barometric pressure sensor circuit fault (for GS300 & SC300 models)
Code 41 and Code 47 Throttle position sensor circuit fault
Code 42 Vehicle speed sensor circuit fault
Code 43 Starter signal
Code 51 Switch condition signal fault (for ES300; GS300 & SC300 models)
Code 52 Code 52 and Code 55 Knock sensor circuit fault
Code 71 EGR system circuit fault (for ES300; GS300 & SC300 models)
Code 78 Fuel pump control circuit fault (for GS300 & SC300 models)

 

How do I tell what terminal is TE1 and E1? Thank you!

 

In the diagnostic box, there should be a print that tells you which is which.

 

Very helpful information for everyone.

 

I want to add to this. You can also test all kinds of various circuits too. Such as O2 sensors and etc. Its a great tool if you have have the service information. For example you can test cooling fan operation by jumping E1 and OP1. E1 is a universal ground. If you have codes, you can jump E1 and TE2 and when the fault occurs, the MIL light will come on at that exact moment. Very useful.

Oh and code 55 is the knock control circuit and in such a case you would replace the PCM but ive never heard of that code popping up on any applicable OBD 1 Toyota.

 

Turns out, according to lexus factory service manual, code 21 is left bank [radiator side] oxygen sensor and the code 28 is the right bank [firewall side] oxygen sensor [ 02 sensor ].

 

''pulling the efi fuse for 10 seconds'' doesn't clear the code. all it does it break the white plastic part that secures it when you remove. just advice for the common man. sol'n is to unplug battery cable and press brake pedal for a couple seconds. then, there will be a good reset.

 

It often clears the codes. Wait.. what did you break?

 

I have a 95 sc300 and my check engine light is on due to code 21. Thats just the O2 Sensors right?

 

21 is left bank pre cat for my car

imtaking small pic of efi to show you, badviper

 

Oh and code 55 is the knock control circuit and in such a case you would replace the PCM but ive never heard of that code popping up on any applicable OBD 1 Toyota.[/QUOTE]

I have a code 55 on a 93 ES300. is a PCM the only fix?

 

I have a code 55 on a 93 ES300. is a PCM the only fix?[/QUOTE]

Yes. Is that the only code you have?

 

replace the ecu right away? no way, try checking the circuit which is to say the connections and wiring first

 

That circuit is in the pcm only.

 

Strangely enough, my '93 popped up a 55 code last week (knock sensor 1)!! Should I replace both knock sensors (I've heard that it's better to do so) or just replace the bad one?? 55 is the only code that is coming up.