Question: "SYS" trouble codes meanings?

[wrenchmantee]

My "SYS" light in the speedo cluster comes on flashing alot, then quits for a few minutes, then back on and on. I did find the proceedure to get the codes using the speedo, but I have not been able to tell what they mean. Does anyone have a way to tell what each code is saying? The only other light coming on is the ASR light. H41, H51, H72, H74 (FYI, I do have a TBI Hot chip in the ECM) ;help

 

[Rabbit]

This site shud help you out.......

http://www.corvettephotographs.com/c4vettes/index.htm

 

[Hib Halverson]

If the "sys" light flashes, that means you may have CCM codes set.

To decode the codes you need to not only know the code numbers but also what diagnostic mode was running at the time those codes were shown.

Without knowing the mode you've got the IPC in, when you say the "ASR light" is on, I'll assume you mean "Service ASR". If that light is on, I'll make the easy guess that the codes you saw may be ABS/ASR faults.

H=history code, ie: set in the past but not present during the current diagnostic session.

ABS/ASR DTC 41 and 51 are BPM faults.
71 is a serial data line malfunction
74 is a low voltage fault

I'd make sure the battery, battery cables and the alternator are in good condition. Check ABS/ASR chassis grounds. Check other ABS/ASR connections at the ABS/ASR controller.

if all is well with that, then I've flush the brake system per the service manual.

Then, I'd clear codes per the service manual and road test. If the Service ABS/ASR light stays off and the IPC doesn't flash "SYS" you're good to go. If the codes return, you need to diagnose each per the manual.

I should add that all the information on CCM diagnostics, and that of other controllers, is in the factory service manual. if you're going to attempt solution of those codes on a DIY basis, purchase of a manual is advised.

 

[wrenchmantee]

Thanks for all the info, I did not mention that the module code # was 1 or 7 ??? I could not tell. Second, no I don't have a service manual...But, I can bleed the brakes easy enough. I did see one or two things that might help. There is a small sensor on the lower part of the master cylinder that has been wet lately. The local parts store shows it as part of a new master cylinder but, not as a single part. Any clues what sensor that is?
My guess would be a by-passing sensor of the master cylinder. The other possiblity for the "SYS" is the replacement of the radio with an aftermarket, I read that the OEM radio acted as a voltage resister to lower the voltage going into the speedo/led causing the problem....What do you think?

 

[Hib Halverson]

(snip)
What do you think?

I think you need to buy a Service Manual for your model year. You cannot effectively do DIY maintenance/repair without one.

It is possible that you may have a problem with the BPM. Before you just go replacing it (you'll give birth when you find out the cost) you need to follow the instructions I posted earlier including flushing the system per the Service Manual. If the codes still set, then you need to trouble shoot per the Manual. Also, last Fall "Corvette Enthusiast" magazine published a two-part series on C4 ABS/ASR service. If you can find those magazines, the stories might be helpful.

Typically, there can be two sensors in the master cyl. assy for that year. The one screwed into the bottom of the reservoir is the fluid level switch. The one screwed into the cylinder body is the pressure differential warning switch.

 

[JAKE]

Thanks for all the info, I did not mention that the module code # was 1 or 7 ??? I could not tell. Second, no I don't have a service manual...But, I can bleed the brakes easy enough. I did see one or two things that might help. There is a small sensor on the lower part of the master cylinder that has been wet lately. The local parts store shows it as part of a new master cylinder but, not as a single part. Any clues what sensor that is?
My guess would be a by-passing sensor of the master cylinder. The other possiblity for the "SYS" is the replacement of the radio with an aftermarket, I read that the OEM radio acted as a voltage resister to lower the voltage going into the speedo/led causing the problem....What do you think?

There's an on-going thread right now about how installing an after-market radio can cause a 'SYS' light to flash.

From all I've read, installing two resistors in certain wires to the radio is the fix. Seems the CCM looks for a certain resistance that is absent when the stock radio is removed and an after-market unit is installed.

Check for the posts which'll show which resistors to use; they should be right near the top of the posts on this board.

Jake

 

[vette079]

Did the sys light come on when you replaced the radio with another one. That might narrow down the search. If you still have the original radio or know one that has a vette radio (even if it doesn´t work), connecting the original radio to the original wiring, you can find out if the sys light comes up. If not... Proceed as mentioned before (the thing with the resistor in the new radio. I don´t know for sure about history codes but don´t they just stay in the memory until you reset them or disconnect the battery cable for more than ten seconds? Someone?

 

[wrenchmantee]

Nope, the radio is long gone....But I have disconnected the battery many times since. I really don't care that it comes on quite often, it's that it screws up the mpg and range computer readout everytime I try to use them. Is there a way to just bypass the damn "SYS" thing? What is the "SYS" referring to?

 

[JAKE]

The "SYS' light coming on after the installation of an after-market radio is a common occurrence. There's even a Techincal Service Bulletin addressing the issue and involves installing two resistors to the radio wiring.

The TSB is 93-68-9A and the resistors can be purchased at a store like Radio Shack/Frys for a dollar or so.

As I wrote before, track down and read the thread that's on-going right now. After I wrote to Paul informing him of this, he found it and posted it in that thread.

Jake

 

[Paul Higg]

Nope, the radio is long gone....But I have disconnected the battery many times since. I really don't care that it comes on quite often, it's that it screws up the mpg and range computer readout everytime I try to use them. Is there a way to just bypass the damn "SYS" thing? What is the "SYS" referring to?

I can help you out with the SYS light if it is an aftermarket stereo. After much help from Jake I know exactly what steps to take to eliminate the SYS light. By the way, from looking at my wiring diagrams of my 94 LT1 a DTC code 72 will fault in module 9 if the SYS light is caused by the stereo. What needs to be done is a simple mod, you need to splice two 1K ohm, 1/2 watts resistors to a hot wire, and the other ends to two separate wires. That will fake out the dimming circuit as almost all new aftermarket stereos do not have a dimming circuit.

Here's a quick check, during daylight, put your finger over the ambient light sensor located directly left of the "Trip Monitor" words. Hold your finger there and see if the SYS light flashes. If it does you have to do the mod. I can guide you through the entire thing. I have a lot of experience reading wiring diagrams so looking at the DTC codes I got I did some research in my FSM. The DTC code 72 on the EBTCM module may look like it is a faulty transmission speed sensor but that circuit is tied in DIRECTLY to the radio system because the stereo volume is supposed to increase when the car is sped up. The DTC code 72 (coincidence) in the CCM is the ambient light sensor. Don't throw any parts at it until you do the mod.

I can tell you how to use the trip monitor panel to reset the codes, drive it a mile or so and interrogate it again and then we will see what modules are giving what DTC's. I will be happy to help you if you do not have an FSM.

Chevy was very clever in the way they used the OBD plug in conjunction with the trip monitor buttons. You can tell it to run a complete check on almost every single system on the car. Relays will click, things will activate, etc. It is cool. JUST like an airplane. I love this thing now that Jake has enlightened me on how to use it and I would be totally lost without the FSM.

That radio and the SYS light and the accompanying DTC's are almost entirely because of the new stereo. There are so many wiring diagram connections to the CCM that will cause a DTC which are all linked to the stereo, I could not believe it until I spent an evening cross referencing every single wiring diagram that relates to the radio head. What a complicated mess. I just wish I knew if there is a stereo out there that has auto dimming, and auto loudness.

Let me know if you need the help. I have the TSB and the diagrams and detailed instructions on how to do it. I plan on doing mine as soon as I can take it out of service and I am going to take detailed photos and make a detailed description on how to do it. In fact, today I brought the diagrams and the TSB to Best Buy to help any future C4 owners that will be scratching their heads over the SYS light.

Much thanks goes to Jake and others who pointed me in the right direction.

Paul

 

[Hib Halverson]

The above was quite interesting.

Thanks for posting it.

 

[wrenchmantee]

Yes, that makes it alot clearer....I have just purchased a new dvd on the wiring schematics and your right about the radio is causing these codes. Going to get the stuff at radio shack and fix it. Thanks Again...Wrenchmantee

 

[Paul Higg]

Thanks Hib, and you're welcome wrench.

This is why I like this forum, we all get to help each other. I know it has helped me tremendously.