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94 Computer Cant Be Read Due To Adapter Incompatibility


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#1 extremelyslow

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Posted 12 April 2011 - 02:53 PM

I've got a 1994 Corolla base and I'm trying to get my mechanic to read the computer to adjust the idle on the car and also figure out why it won't switch into 4th gear (new coolant temp sensor didn't help..) and he says the machine he uses to read the computer has a different fitting and can't mate up with the Diagnosis fitting on my '94. Does anyone know if I can get an adapter to get his machine to read my computer or how I can go about reading the computer in my '94?

Thanks a bunch!

#2 fishexpo101

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Posted 12 April 2011 - 03:24 PM

Not sure what the mechanic is after with a scanner as the pre-1996 model year cars are only OBD-I compliant, with very few exceptions, and do not need a scanner to pull codes from the ECM.

There is a diagnostic port that is under the hood that you can run jumper pins to retrieve any malfunction codes. Once those pins are shorted, any codes stored will be flashed on the MIL display (check engine lamp will flash the codes for you). If you are one of the lucky/unlucky one to have the semi-OBDII compliant 1994 car, then there is very little recourse for you. OBD-II scanner will work, but the codes retrieved may not be valid, as there was not set standard at that time. As far as I know, only Toyota Camry, Toyota T100, and Toyota Previa were affected around that time period.

Also, if I recall correctly, only the DX and LE trim models came with the 1.8L 7AFE engines with 4-speed automatic transaxles, the Corolla base model only came with a 1.6L 4AFE engine and 3-speed automatic transaxle. I just asked, as if you have the base model, that will be a 1.6L 4AFE with an automatic, you'll not find a 4th gear because there isn't one. If you have the 1.8L engine, then you would likely have the 4th gear (verify by looking for the overdrive button switch on the shifter itself).

A mechanic should be able to diagnose a pre-OBDII vehicle without the need of the scanner - if he cannot, due to an "adapter" issue, I would highly recommend to start looking for another mechanic.

If you want - you can list what issues you are running into with your car, mileage, recent work done, etc. as there is likely a poster here that has run exactly into the same situation. That way, if you plan on sticking with this mechanic, you can help point him in the right direction - another diagnostic avenue to pursue.