Intermittent SES light

'95 SC 101k miles, all stock......
Over the last few months I've seen my SES light come on maybe three times. It will stay on while driving but if I shut the car off, the next time I drive it the light is off. I've noticed this happened when I switched brands of gasoline. Normally I run Chevron supreme. I noticed this latest SES light was after fueling with Shell premium. The SES is off again and has been for about the last 150 miles.

Any ideas on what would cause this intermittent SES?

I bought the ALDL usb cable and have been trying to get the Tunerpro software to work but no luck so far. I'm now going to try the EFILive software.

Hi, Steve. The way to know for sure is to scan the car for the DTC code (it will be stored for all the times your SES illuminated). Chances are the fuel has nothing to do with it, but there might be something else going on that is affected by the fuel, or it could be coincidence.

The way the PCM "thinks" is in numbers of trips (on, drive, off cycles) vs. DTCs are detected. Some trouble codes are not as important on the hierarchy of priorities, so 1, 2, or 3 trips must be made before the SES is illuminated. Some DTCs are high priority, and so will illuminate during the 1st trip. The same system applies for turning the SES lamp off, as different codes require 1, 2, or 3 trips with no detection before the lamp will go out. All of this can seem random, especially when there is more than one DTC tripping the lamp, but the PCM is really turning the SES lamp on and off according to a set of rules programmed into its memory.

Good luck with your problem. It could be a sensor, the transmission, or pretty much anything that's not 100% mechanical. Get the scan and let us know what codes you find. Hopefully it's nothing serious.

I have the same problem. Havent really noticed a pattern, but ever since Ive started filling up with premium the light has been on 99% of the time. I haven't really checked it out that much but ive noticed a lot of oil leaking around the pan. Could be that.

Keep posted

Aaron,

Thanks for that excellent rundown on how the PCM "thinks" and assigns the priorities to the SES lamp off and on. I honestly didn't know that. So now I know its not really "random".

If I don't get a scanning software product to work pretty soon with my ALDL cable I will have to take the car to my mechanic to read the codes.

In any event I will post whatever I find out about my SES.
Thanks again!
Steve

No problem Steve. I copied some of the PCM program info from my Series II tuner software. This shows the options for SES lamp illumination. It may not be exactly the same as Series I, but probably close:

Category: Diagnostics / Fault Reporting / DTC Fault Type

Min Value: 0
Max Value: 3

Parameter Description:

0 = 1 trip SES on, 3 trips SES Off.
1 = 2 trips SES On, 3 trips SES Off.
2 = SES On.
3 = No Report.

Code Data:













For definitions of DTCs, see this link: http://www.actron.com/code_lookup.php