stupid obd1

[z28camaro94]

alright i have a problem with trying to get the codes out of my 94 z28.
i have tryed multiple scanners and they all say cannot communicate with vehicle. i checked all the fuses, they are all good. i have good ground and the A terminal, 5v coming out of the B terminal, 4.6v coming out of the M terminal, and 6.8v coming out of the G terminal.

A terminal being ground
B terminal being the field service enable
M terminal being the serial data line
G terminal being program input for keyless entry

idk wat the f***in problem is. i doubt that any of the wires are shorted since i have voltage coming out of them.

i tried the jump method a couple of days ago and was able to get the codes to flash out, but i didnt know how to read them at that time so i didnt record them. i tried the jump method again today and it doesnt flash the codes. i've read up that the 94's wont flash the codes out, well then y did it work the other day.

also the check engine light is NOT on. it came on last wednesday for all of 30 seconds then went back off. i am trying to see what the code was that popped on. hoping that its still in the memory. i have not disconnected the battery since about a month ago so im assuming that the code is still in there.

can anyone help?

[z28camaro94]

also i doubt it is the PCM because the car runs and drives perfectly. but then again when it comes to wiring, i know conventional thinking doesnt always apply

[LTb1ow]

Early 94s will flash the codes, I would try a scanner made for OBD1.

[Blacdout96]

We used a scanner for OBD1, as well as taking it to several shops, with all of them getting the same problem, which would be unable to communicate twith the computer. I tld him the easiest thing to do is sell boat anchor, aquire LS bliss, and become touched by god. I cannot since I'm sinned by the V6.

[z28camaro94]

not getting rid of the lt1. yes an LS would be nice but not in the budget now. just need some freaking help with this damn computer

[sweetbmxrider]

To extract a trouble code from the computer for diagnostic purposes, the twelve pin data link connector (DLC) is used.
The DLC is located in the passenger compartment. Terminal B of the connector is the test terminal and terminal A is the ground used for diagnostic display.
If the test terminal is grounded with the ignition on and engine not running, the system will enter the diagnostic mode. In this mode, the computer will display a Code 12, three consecutive times, by flashing the "CHECK ENGINE" or "SERVICE ENGINE SOON" light. A Code 12 consists of one flash, a short pause, then two flashes in rapid succession. After Code 12 is displayed, any stored trouble codes will be displayed by flashing the "CHECK ENGINE" or "SERVICE ENGINE SOON" light. All codes are displayed 3 times each then a code 12 will repeat. In the diagnostic mode, the computer will also energize all computer controlled relays and solenoids

If the test terminal is grounded with the engine running, the system will enter the field service mode. In this mode, the "CHECK ENGINE" or "SERVICE ENGINE SOON" light will indicate whether the system is in open or closed loop operation. If the system is in open loop operation, the light will flash approximately two and one-half times per second. Closed loop operation is indicated by the light flashing approximately once per second. A "Scan" tool can be used to enter the "Field Service Mode."

Connector D Terminal 30 on the pcm is for serial data communication. Ohm it out to the DLC. Maybe someone local has a known working 94 computer that you can swap in and check for communication after verifying communication in the donor vehicle.

[z28camaro94]

thank you def helpful. do u know what it should ohm out to? i will try a diff comp when i can get a hold of one

[sweetbmxrider]

pretty much 0. If it has a break, it won't show resistance.