SYS light flashing - just replaced battery.

[JAKE]

Okay, here it is:

The system diagnostic check is an organized approach to identify problems associated with the Central Control Module (CCM). It must be a starting point for any CCM complaint, because it directs the service technican to the next logical step in diagnosing the complaint. The CCM itself is a very reliable component and is not likely the cause of the malfunction.

If the problem is intermittent, try performing the tests shown while "wiggling: wiring and connectors. This can often cause the malfunction to appear. Check for poor connectors at both the CCM and related components.

The CCM uses the speedometer, odometer and the trip monitor located on the instrument cluster to display information while in the diagnostic mode. The buttons on the Driver Information Center (DIC) are used to send instructions to the CCM when in the diagnostic mode.

DIAGNOSTIC MODE: To enter the diagnostic mode, ground terminal; "12" of the Data Link Connector (DLC) and turn the ignition switch to the "ON" position. Terminal "12" is on the lower row fourth from the left. The ground terminal is number "5", top row, fifth from the left.

After the ignition to "ON" the CCM will display any Diagnostic Trouble Code (DTC) in an automatic display sequence. The CCM is module 1; the PCM is module 4, the RTD (Real Time Damping) is module 7, the ABS/TCS EBTCM (Electronic Brake and Traction Control) is module 9 and the DERM (Diagnostic Energy Reserve Module) is module "A".

When in the automatic display sedquence, each DTC is displayed for three seconds followed by a one second pause before the next DTC is displayed. When all the DTCs have been displayed for all modules, the trip monitor will display 1.0 and the speedometer will be blank.

Write down the displayed DTCs as they appear. Look up what the code number means and follow the trouble -shooting directions in the FSM to track down the cause.

There's a way to display each module's info manually but it's more involved (take a lot more typing) but if you need it I can post it later.

Hope this helps.

Jake

 

[Paul Higg]

Thanks Jake! Now here's a question. I have a 94 LT1 but the diagnostics plug has only 10 pins. The FSM shows two plugs, one with 12 pins and the other with, I THINK 16, I don't have it in front of me. Anyway, when I am looking straight at it, how do I know which pin is which number?

Sorry but I am totally new to this, I have the ability I just need to familiarize myself with the car. This is one complicated piece of machinery. It reminds me of what we used to say about helicopters in the Air Force. "One million parts flying in close formation."

Paul

 

[JAKE]

Thanks Jake! Now here's a question. I have a 94 LT1 but the diagnostics plug has only 10 pins. The FSM shows two plugs, one with 12 pins and the other with, I THINK 16, I don't have it in front of me. Anyway, when I am looking straight at it, how do I know which pin is which number?

Sorry but I am totally new to this, I have the ability I just need to familiarize myself with the car. This is one complicated piece of machinery. It reminds me of what we used to say about helicopters in the Air Force. "One million parts flying in close formation."

Paul

Remember, I prefaced my comments by saying the info is for my 96.

On my 96, pin numbers on the under dask link are numbered from left to right - as you sit in the driver's seat -. The top row is numbered 1 through 8; the bottom row is numbered 9 through 16; from left to right.

You can reference your Factory Service Manual (FSM) or even use GOOGLE to find a site that shows how the pins are located on your year Vette. You may be able to find how to pull any DTC codes on-line too.

Once you energize the diagnostic mode, the stored codes will flash on your dash display, but you'll still have to look up what they mean. You'll also need a FSM to be able to follow through the trouble-shooting procedure to zero in what causing the 'SYS' blinking.

Hell, even the trouble-shooting info may be on-line too. Give it a shot.

Jake

 

[Paul Higg]

Thanks Jake. I see you have a 16 pin plug. Someone told me that on the 94 GM had a mixture of cars made with different diagnostic plugs. I will have to do some more research.

I have the FSM, all I gotta do is make sure what pin is what and run the diagnostic, look up the code and see what I can see.

This thing is SO intermittent though and it's all related to the electrical system. I just hope that when I do interrogate it I will have a stored code. Otherwise I will have to try to wiggle wires, etc. Thanks for your help.

Paul

 

[JAKE]

Thanks Jake. I see you have a 16 pin plug. Someone told me that on the 94 GM had a mixture of cars made with different diagnostic plugs. I will have to do some more research.

I have the FSM, all I gotta do is make sure what pin is what and run the diagnostic, look up the code and see what I can see.

This thing is SO intermittent though and it's all related to the electrical system. I just hope that when I do interrogate it I will have a stored code. Otherwise I will have to try to wiggle wires, etc. Thanks for your help.

Paul

Pin "12" seems to be the common pin GM uses to pull codes. On the 1986 (eighty six) TPI I had, pin "12" was also the one to use, althugh the ground pin wasn't #5 - it was different. Question is 'which pin is pin "12" and which pin is pin 5?

The 94 must be using a combination of OBD1 AND OBD2 connectors. I'll bet if you look closely at the
data Link Connector you'll see that not ALL pin locations are used. One or more will be empty, just an empty hole with no metal connection inside the little pin opening.

You can use GOOGLE and type in something like "1994 Corvette Data Link Connector" and I'll bet you'll find a site showing a picture of the Connector for your 94 with the terminal numbers shown.

Also, there's a separate section in the FSM that deals with tracking down intermittent 'SYS' problems. If you aren't able to find a stored code using the procedure I previoulsy listed, drop me a line and I'll see if I can help you track down your intermittent problem using the Intermittent procedure shown in the FSM.

Don't feel badly about not knowing this system, my son doesn't either. He's a 2nd year Cadet at West Point and I bought him a 96 Vette as a reward for being accepted. He doesn't know the system either so I've been helping him learn it too. In fact, I'm still learning the 96 system too, after spending years learning how the 86 system works.

Jake

 

[Paul Higg]

Jake! I found a way to duplicate the SYS light. It was serendipity. I was driving today and when I went under a bridge the light came on. The bridge was casting a shadow and it darkened the Trip Monitor sensor. I was WONDERING what that was for. Anyway, I can now duplicate the SYS light all day by putting my finger over the sensor. So now I have to look in the FSM (still haven't had the time) and find out how it works. Does the sensor send a signal to the CCM then to a dimmer? Does it send a signal directly to a dimmer? At least I can duplicate it all day.

I will take your advice and Google the connector. You are right, there are several empty holes in the connector.

http://www.corvettebuyers.com/ecm1.jpg. I found this. This is what mine looks like.

I will try to look in the FSM and look at wiring diagrams and see how the system works. This is fun, it's like troubleshooting a 767. I used to be an avionics A&P on big jets. "Duping" a problem is half the battle.

Paul

 

[JAKE]

GREAT!! That points us in the right direction.

Unfortunately, I preparing to attend a presidental rally this evening, so I don't have time to look it up in my FSM right now. When I return, which will be well after 10PM, I'll see what my FSM has to say about that sensor and how to fix the 'SYS' problem it's causing.

I'll post when I have anything that'll help.

Jake

 

[Paul Higg]

Jake, you're a great asset to this forum. I really appreciate all the info you have given me and the patience you have shown. Enjoy the rally.

 

[JAKE]

According to my FSM for the 96, we're talking about the Ambient Light Sensor A/D Counts, Data ID number 03.

The courtesy lamp system does not operate if there is a substantial amount of ambient light (i.e. it is not dark outside). If there wee a malfunction with the ambient light sensor circuit in which the CCM was always interpreting that it was daytime outside, the CCM would never turn the courtesy lights "ON" To check this possibility, select the data display function; then select the ambient light sensor data (Data ID 03) When the data is displayed, cover the light sensor and see if the data value changes. If not, the light sensor may be malfunctioning, there may be a wiring malfunction etc.

That's what the FSM says. I need to know if the Courtesy lights come on or not. Does everything else work? Like the power window, power mirrors, etc.

There're separate procedures to be followed depending on what's actually happening.

Let me know and I'll look farther.

Jake

 

[Paul Higg]

Jake, I read the same thing in my FSM too. I am scratching my head though.

The courtesy lights do come on, power windows work, power mirrors, all ok.

There might be a related problem too. We now have SOME chimes after running it through an automatic car wash. !?! But the chimes only worked when the seat belts were unbuckled, we started the car and my wife and I did not have the belts buckled. This time instead of a mere bip of a chime, it chimed until the belts were buckled. However, the chimes still do not work when the lights are left on, or opening the door with the engine off and the key in the ignition. I was wondering if the ignition key cylinder may be going on the fritz.

Also, I have YET to take a photo of the OBD plug. I have seen so many varieties it makes my head spin. Some 94's have the same plug I do but with a different amount of pins, different pin placement, etc. I will attempt to take a photo and post it somehow, or send it to you. Or make a drawing of it.
Your help is very much appreciated.

 

[Paul Higg]

Jake, here is a photo of my OBD plug. If the FSM is correct then I can jumper the pins and read out the codes. Tell me what you think about the plug. Also, notice that the metal tab is bent on the right side.

DSCN2073.JPG

 

[JAKE]

Check this site; scroll down to the bottom of the page and check out what's written about your 94.

Hang on, let me check out those URLs

We're slowly getting there.

OK. http://www.corvettebuyers.com, then click on the box to the left entitled C4VETTES.COM then click on FACT SHEETS, then click on TROUBLE CODE RECOVERY

Jake

 

[Paul Higg]

Jake, no matter what browser I use I get a "Page Not Found" error.

Anyway, going back a few posts, the courtesy lights, are they the little reddish lights that are always on? Like in the rear view mirror on the right side? Or in the doors? They work.

I took a photo of my plug today and it came out pretty good.

It is an OBD II plug, I wish you could see the picture because the bracket seems bent and the plug looks a little crooked. I wonder how that happened?

Here are the pins it contains

Pin 1, empty, pins 2, 3, 4, 5, 6 have pins, pin 7 empty, 8 & 9 have pins, 10 & 11 no pins, 12 has a pin, 13 no pin, 14 has a pin, 15 no pin, and 16 has a pin.

Thanks again Jake.

 

[JAKE]

Have a pen/pencil and paper ready.

Take a piece of thin insulated wire about 4 inches long. Strip the insulation off both ends of the wire and twist the exposed wire tightly. Bend the wire in half, into like a horse-shoe shape. Insert one end of the wire in to pin 12 and the other end of the wire into pin 5. You've just grounded pin 12.

Now turn the ignition key to "ON" but do not start the engine.

The codes will flash in the speedometer area of the dash cluster. Write down any codes you see flash and post them here.

Jake

 

[JAKE]

Jake, no matter what browser I use I get a "Page Not Found" error.

Anyway, going back a few posts, the courtesy lights, are they the little reddish lights that are always on? Like in the rear view mirror on the right side? Or in the doors? They work.

I took a photo of my plug today and it came out pretty good.

It is an OBD II plug, I wish you could see the picture because the bracket seems bent and the plug looks a little crooked. I wonder how that happened?

Here are the pins it contains

Pin 1, empty, pins 2, 3, 4, 5, 6 have pins, pin 7 empty, 8 & 9 have pins, 10 & 11 no pins, 12 has a pin, 13 no pin, 14 has a pin, 15 no pin, and 16 has a pin.

Thanks again Jake.

SEE MY ABOVE POST FOR THE PROCEDURE TO LOG ON TO THE SITE.

You can also use Google, type in "1994 Corvette SYS codes" to get more sites.

Jake

 

[Paul Higg]

Excellent site Jake, I have it bookmarked. Thanks.

Now that I know exactly what to do I will do it as soon as I get a chance. My wife and her Mom keep me pretty busy but I will attempt it today.

I really appreciate your help and basically holding my hand as I go through this learning process Jake. I guess learning how to do something new is the hardest part.

I will get back to you soon.

Paul

 

[Paul Higg]

Jake, this is what I got: per my FSM

1. CCM module C72 & H72
4. ---
9. ABS/ASR module H72
A. ---
1.0

It appears to be a problem in the dimming circuit. I reset it. I also ran the test of covering the ambient light sensor with my finger and put on the parking lights and dimmed the lights, it works fine.

Now, there is a paragraph which I will quote which is VERY interesting.

"A DTC 72 may set if an aftermarket radio is installed and the original radio control head dimming control lines have been left open. Refer to dealer service bulletin for repair information."

Well, I had Best Buy install a Sony MEX-BT2500 stereo. Funny thing is it doesn't dim. I thought that was unusual but now it all ties together. Of course the stereo manual doesn't come with wiring diagrams.

Now, how would I go about getting access to that service bulletin?

I am going to take with the manager as I e-mailed him before about the chimes being dead. I will bet a million bucks the installer messed up a plug on the CCM that controls the dimming circuit and the chimes, or I have to somehow jump a wire to fix the radio dimming circuit. What is your opinion?

Thanks Jake.

Paul

 

[JAKE]

I've read on other forums that the installation of an after-market radio will cause the 'SYS' light to flash. This is caused because the CCM is looking for a certain resistance which isn't there any longer.

The simple fix is to install a certain resistor on a certain wire to "fool" the CCM.

I don't recall all the specific details because at the time I read it, I didn't have a particular need for it. Anyway, do a SEARCH here first to see if anything has been posted on that problem.

If that fails to turn up the procedure, go to forums.corvetteforum.com and do another SEARCH there. That's where I saw the procedure posted, if memory serves.

Keep us posted and when you locate the procedure be sure to post it here so others who may need the procedure can have access.

Jake

 

[JAKE]

I forgot to add this:

Remember, GOOGLE can be your best friend. Whenever you have a question like tracking down a service bulletin, go to Google. I believe the correct name is TECHNICAL SERVICE BULLETINS (TSB).

Sites, like ALLDATA, have all of them listed, but they're for sale. Other sites that'll pop up may have them listed for free. Also, links will show up to other Forums where someone else is having the same problem and the bulletin may be included in his/her thread.

It's just a matter of spending time on-line, reading posts on the various sites and you'll usually be able to find your answer. I often refer to it as "Doing Your Homework".

Hope this helps.

Jake

 

[Paul Higg]

Thanks for the post Jake. I will search for the resistor and keep you posted.

As for Google. I tired in vain last night. I even went to GM's web site but it kept saying my VIN was pending or something like that so I didn't have access to any service bulletins. I was planning on calling my local Vette dealer and asking them about the particular service bulletin that covers it. But since you have seen that it is a resistor I am more inclined to believe that because after looking at the codes and the wiring diagrams, it ALL ties into the radio control head circuit. Even the ARS/ABS system which is supposed to make the volume louder when the car is driven faster. It comes from the transmission speed sensor and is sent to the CCM, so no wonder it showed up as a fault on module 9.

This is fun.

Thanks Jake.