twcblackhand6970

I took my car to autozone to get them to pull the codes for the SES light, and no codes came up. The SES light stayed off when he plug his thing in. Why weren't any codes returned? 94 LT1

Injuneer

How long was the SES light on for, before you took it in? Was it still on when you drove in? If it turned off before you drove in, how long was it off? Then, when he turned the key to "on", to do the scan, it was no longer on? Was he able to get his scanner to "connect" to the PCM (he would get an "unable to connect" message if he used the wrong scanner)?

twcblackhand6970

He had some plug thing that connected to the PCM. He turned the key to the on position and the light came on. He then plugged his thing in and the SES light went off and didn't blink like it was suppose to. Then he unplugged his thing and the SES light came back on. He said it wouldn't give him any codes. The rear gears of the car have been changed to 3.73 and it has no cats and longtube headers, could this be causing the SES light to come on with no codes?

Injuneer

He used the wrong scanner. He assumed that he could use a scanner that shorts the pins in the ALDL connector, and flash the codes on the SES light, counting the blinks to determine the code. The 1993 LT1 was the last year where that works. For 94 and 95 LT1 engine/PCM's, you need a "real" OBD-I scan tool, that communicates directly with the PCM and shows you the codes on a screen. You can get used OBD-I scanners made by Auto Xray for less than $100, and they will read your codes, and the sensors and other engine operating parameters. But don't be fooled by the $30 Actron "scanner", because it is nothing more that a switch that shorts the ALDL pins, and it won't work.

Nothing you have done to the car will cause the PCM to not supply codes. He used the wrong scanner.

twcblackhand6970

So all the mods the previous owner did should cause the SES light to come on?

2000GTP

Its possible, but hard to say without knowing the exact codes.

Injuneer

Changing gears, deleting the cats in OBD-I, and longtube headers generally would not cause codes. You might sometimes get DTC 32 for poor EGR flow with a very low back-pressure exhaust system, but not usually a problem with OBD-I.

twcblackhand6970

Well, I went to autozone again and told him my car was OBD-I, they said they only did OBD-II. Need to find a mechanic that can do it for cheap.