1991. I read many of the old posts on the "sys" problem, tried a bunch of things and i still have the flashing sys. Here's what i tried:

I load tested the battery (I have a tester) and the battery is in the good range.

The voltage at the batt is over 14 volts with the car running. I assume this means the alt is fine.

I pulled the trouble codes. no codes.

I checked all the fuses. all fuses look good.

I removed the aftermarket stereo(even though I have had the stereo for years with no flashing "sys"). "SYS" still present.

What else can I try? I'm stumped.

Howdo

 

When exactly does it flash, does it stop the engine from running, what code is it flashing? Have you tried resetting it by disconnecting the battery?

 

It flashes about every 15 secs. It doesnt stop engine from running. I tried resetting by disconnecting the battery, but no luck. There are no codes.

 

You removed aftermarket stereo, what did you replace it with?
If a prev. owner put it in, he must have put in a resistor somewhere as well.
Could be something wrong with that one.

 

What is the "sys" light? This is a picture of my 87s telltale panel.



No "sys" light!

 

As far as I know you don´t have SYS.
Came in 1990, with the new dash.
SYS shows where you normally will see the average milage and range information left of the speedo on 1990-1996 models.

 

OK so SYS is for later models but does the same as "Check Engine" on early models.

I would think it would be a good time to use a scan tool. Otherwise ignore it or change the ecm. Nothing in the manual talks about 1 flash every 15 seconds.

 

Nope, SYS and SES are two different animals.
SES is the ECM saying... dude somethings up with your engine, ABS, that sort of stuff...
SYS is the CCM saying... dude somethings up with your safety gadgets or your powers about to go down... kind of...

The SYS warning comes up when you put in an aftermarket stereo for example.
You can put in a resistor somewhere (don´t know where), then the SYS warning will go away.
SYS can come up when your alternator/battery is going south, because the system isn´t getting enough power to run.

Hope you got the picture... kind of.

And it´s never a bad thing to buy/have a scanner, I bought an autoXray 6000 a few years ago, that in combo with a FSM saved me buxbuxbux...

 

OK that is interesting to know. So how can an aftermarket stereo cause the "sys" light to come on? Is it due to the constant power feed to it when the ignition is off to keep the stereo memory going draining the power too much? Maybe a resistor in the power lead reduces stereo current and hence volt drop with ignition off stopping the nuisance flashing light.

 

Not sure how that works, what I would like to know is, if the pre 90 models also get some kind of warning (when replacing stereo), since you don´t get this SYS light.

The original delco/bose has a feature called SCV (speed compensated volume).
The faster you drive, the higher the volume, so it must get a VSS signal from somewhere.

That´s the only thing I can come up with for the SYS warning coming up when going aftermarket.
There is a datalink between the delco/bose and the CCM.

Maybe someone can chime in on this yes/no SYS on pre 90´s.

 

Found this on the internet:


"CCM (Central Control Module) Codes 72 and 74 usually occur after the radio control head was replaced. The radio head LED and LCD open circuits are noticed by the CCM, setting the code. There is a simple fix while the radio head is being replaced. Resistors and one diode must be installed to alleviate the problem. A 1K 1/2 watt resistor is installed in the following manner: one side of the resistor must be powered by the radio head C2 connector in position 8 (pink wire). Connect one end of the resistor to this wire. This will send the correct voltage signal to the CCM once the other side of the resistor is connected. At radio head connector C1, locate the gray/black striped wire at position 3. Connect the other end of the resistor here. Be careful: the radio head has two gray/black striped wires in connector C1. The gray/black striped wire at position 4 is the incandescent lamp control. It will not set a code when left disconnected. To recap: the resistor will be installed at connector C2 position 8 on one end and connector C1 at position 3 for the other end.

LED dimming circuit

The purple/white striped wire at the radio head connector (C1 position 2) requires a 10 Ohm resistor and diode in series with the pink wire. The same pink wire from connector C2 position 8 is used for power. Connect one side of the 10 Ohm resistor to the pink wire. The diode should be installed in series with the resistor. Diodes are an electrical check valve allowing current to flow in one direction only. Diodes have an arrow on their barrel denoting direction of current flow. The arrow should point away from the resistor towards the purple/white striped wire. One side of the diode connects to the resistor. The side with arrow pointing out goes to the purple/white striped wire. This will prevent “SYS” from flashing while you’re enjoying the new sound system."

I think this is what the problem with aftermarket radios and the sys light is.

 

Yeah, you´re right, and I forgot about the LED dimming circuit.
But does the pre 90 have or not have the SYS, since there was a delco/bose available as well?

 

if the screws come loose on the DIC you will get the sys flashing on the digital speedo. try pushing in on it a bit and see if that makes it stop.

 

Here is the TSB regarding the resistors that are required when an aftermarket radio is installed in 90 to 93 models with factory Bose.

http://www.corvetteforum.net/c4/dave8476/index4.shtml

There is a procedure in the FSM to read/clear CCM codes.

Luck.

 

I checked for codes, there isn't any codes.

Also, when I say i removed the stereo, I mean that I had an aftermarket unit in there for years with no problem, but just yesterday it took it out just as a troubleshooting exercise. i didnt replace it with anything, the stereo connector isn't connected to anything.

I don't think it is the DIC connection since SYS has been flashing for months, and I just took out the DIC and put it back in last week to work on a different problem.