I have a 98 base coupe. It's got a lot of miles, over 250K. I've slowly worked through a lot of little issues with it but I have one that is just baffling. Every time I drive it now the traction control switches off and on randomly all by itself. I touch the brake, it switches off, touch it again, back on now. Seems like any electrical system I activate, it causes the traction control to flip on and off. It does it with the brake light, head lights, AC compressor cycling, rolling a window up or down. Cant figure it out. It will turn off and on 20 times just running to the store. I know I need a new gas pedal assembly, the throttle response is all over the place, could that be causing this too? Help, I'm a good mechanic, but this is driving me nuts. I've gone through all I know too, TPS is good. Is is a random ground issue? Do I need a new TAC module, anybody heard of this before?

 

When you say the TC is going crazy describe what it is doing. Do you mean it activates every now and then or is it shutting off (TC light on IP and Service Traction Control Message on DIC). What happens when you use the button on the center console to turn off TC?

Touching the brake will deactivate Traction Control as it isn't active during braking. If it is activating while driving around town the EBCM is sensing an unanticipated difference in rear wheel speeds or a sensing both rear wheels are spinning faster than they are supposed to be in relation to the front wheels. Traction control works by cutting torque output and/or applying one or both of the rear brakes.

Check the codes as suggested but think about what causes TC to activate (differences in rear wheel speeds, tire slip). It may be doing just what is supposed to do and you have a problem with wheel speed sensors (although those errors usually generate a ABS code that shuts down the system), tire diameter or some other user controlled item. For instance just the simple act of of swapping the front and rear wheels reverses the tire diameter ratio which the EBCM senses as excessive rear wheel spin and will cause it to activate TC (rear wheel brakes) even when coasting down hill in neutral.

By the way if the gas pedal electronics aren't working TC is shut down because the ECM can't control torque properly.

Bill

 

The TC button works fine, the system just switches off and on very rapidly on its own. I cleared all the codes from the DIC about a week ago, I just pulled them tonight, a lot of U codes for no communication. Heres the list.
PCM- P1416C, I know I need a new check valve, going to do the drivers side on the passenger side work a round.
BCM- U1016H
IPC-U1255H, U1016H, U1064H, U1040H
RADIO- U1064H, U1016H
HVAC- U1064H, U1096H, U1160H, U1255H
LDCM- U1016H
RDCM- U1064H, U1016H
SCM- B2605H
RFA- U1255H, U1096H, U1064H, U1016H, C2110HC, C2115HC

These are fresh codes, I cleared the DIC 1 week ago. On the way home tonight, it did throw the service ABS and Traction control error. Also went into reduced power mode earlier today, they were different incidences.
Wheels are factory stock staggered 17's in front and 18's in the rear, front are 245-45-17, rear 245-45-18. Stock should be 275-40-18 so way too small. Could that be part of it.

 

tires seem small/wrong to me. not sure if this is the problem. but it doesnt help having wrong size tires on the c5

 

Your rear/over front tire diameter ratio is 1:039 which is almost spot on to the stock ratio. When purchasing tires always calculate the ratio don't go by rules of thumb of so many inches larger. The ratio is what counts.

You indicate that pushing the console button turns Traction Control On and Off. However, you didn't answer what happens when you use the button to turn off traction control and leave it off. Does it turn back on by itself?

You mention you saw the Service ABS along with Service Traction Control messages on the DIC. However, I don't see any C Codes indicating any issues with either. C Codes are used for the ABS system. Did you turn the ignition off before you checked the codes? ABS system codes can reset when the ignition is turned off. To make sure you find them you need to check the codes after you see a message and before you turn off the engine.

Also I am going to define some terms so I can be sure we are using the same meanings. TC On means the system is turned on. TC off means the system is turned off. TC active means the system is actively trying to control rear wheel speeds. TC Deactivated means the car has turned TC off due to an error with the engine control system or a problem with something in the ABS system.

98s had several variations of EBCMs depending on when the car was built and whether or not it had Active Handling. Does your car have Active Handling (Option JL4), a front mounted or rear mounted EBCM? Early cars came with a rear mounted EBCM like the 97s had, later cars had two versions of the front mounted EBCM. One for non AH cars and one for AH cars.

Bill

 

I had to turn the car off to enter the diagnostic mode, it wont if the engine is running. When I say the TC turns off and on, it does it by itself. For example, start the car, it turns off, I push the TC button, its back on. I apply the brakes to go into reverse, it switches back off, back out of the driveway, hit the brakes again, TC back on by itself. Shift to drive, it switches back off, touch the brake, back off again. Flip on the headlights, back on. I can literally sit in the driveway, turn my headlights on and off and the TC will switch with them. Same with the window motor, the AC compressor cycling, lighting up the brakes. Its crazy. I can drive 3 miles to the store and the TC will switch off and on 20 times by itself. I can use the button and fight it to stay on but its a loosing battle. I will make a short video of what its doing.

sorry i did miss the TCS codes. they are U1301H, C1226H and U1016H.

Is there a serial cable that could be at fault, there is a lot of communication errors? Also it will randomly go into what I call limp mode, reduced power, it will right itself usually within a few seconds, gauges peg out then return to normal, it was unusual today to have it error out on the ABS and TC at the same time. I know all vettes have wiring and ground issues, but this thing has a mind of its own. This car does not have active handling option.

 

There are several things that need to be investigated.

The symptoms you are experiencing closely duplicate the symptoms seen with the fault related to U1301. U1301H indicates a short between the serial data link and the battery. That short will shut down Traction Control. The H means history so that means the short is intermittent. Take a look under your battery to make sure battery acid hasn't eaten down into the electrical harnesses going to the PCM or onto the PCM. U1016H is a variation of U1301 since it indicates the EBTCM has lost communication with the PCM. I would expect that code if the data link is shorting to the battery. Opens are easy to find shorts are very difficult so you will have to inspect all of the harnesses and data link wiring for a potential short to +12V. Acid damage under the battery is a likely place to start since that is common on C5s. Then look for other places where potential damage to a harness may have occurred.

Shorting the data link to +12V would definitely cause issues with other modules in the car so you do need to find that short.

C1226 indicates a problem that is likely with the age and miles on the car. This DTC can be set anytime the brake is not depressed and no wheel speed sensor hardware DTCs are present, and the EBTCM sees a wheel speed variation of more than 14 Km/h (9 mph) for 2.5 seconds.

I don't know if the wheel hub has been changed anytime in 250K miles but they do get loose and that can cause the variation in signal the EBTCM is seeing. Does your car have a Rear Mounted EBCM and is it an early 98?

After the electrical problems with the data link I think you still may have a problem with the hub, they are a wear out item and you have a lot of miles on the car. Get your car in the air and check each of them. Put your hands in the 12 and 6 positions and see if you can get in and out movement by rocking the tire up and down. Some small movement is OK but if you get a lot you need a new hub. The ABS wheel speed sensor is integral to the hub.

The other thing I would do is check the EBTCM grounds. A loose, corroded or dirty ground is a high likelihood on an older high mile car.

By the way I was able to enter diagnostic mode in both my 97 and 03Z while the engine was running. A 98 wouldn't be any different.

I don't frequent the C5 section very often any more so if you have further questions you can PM me. You can also PM Bill Curlee. He is very active in the C5 section and is very good at helping with C5 electrical problems.

Bill

 

Read the last part of post 6. As 8VETTE7 noted the codes indicate a serial bus issue.

 

I have a 98 base coupe. It's got a lot of miles, over 250K

I read through this post several times and this is how I would troubleshoot:

1. AGE & MILES. The electrical system seems like its having issues. Check the battery and MAKE SURE it is 100% tip top shape in CCA and reserve capacity. Fully charge it and them have it tested at the autoparts store.

2. Our electrical system is divided into TWO parts. B+ Battery "ALWAYS HOT" & SWITCHED "HOT WHEN IGNITION IS ON/ACC". The switched part is WELL KNOWN for causing issues. The contacts inside the ignition switch get burnt and output insufficient voltages. It can be good one day and bad the next. Good under a little LOAD and bad when something else is energized.

EBTCM. The 97 and early 98 was equipped with a rear mounted EBTCM. The mid to late 98 & the rest of the C5 had a FRONT MOUNTED EBTCM. Which do you have??

Regardless of which one you have, you MUST insure that it has proper power and GROUNDS.

The ground LUG on the motor is a common place for high resistance as well as the rear mounted chassis ground G-402 in the passengers rear wheel well. NOTE On all front mounted EBTCM cars, G-402 is there but NOT used.

Motor ground lug:




Most electrical modules are powered by TWO power sources.. Battery "hot at all times & IGNITION (Hot In ON/RUN)

Use a DC Voltmeter and actually measure the voltages at the fuse test points on top of the fuse (to chassis ground) to see what the ignition circuit is providing the module. Low voltages can and will cause a lot of the U series DTCs. I will provide some schematics so you can see the power feeds for the fuses that supply the module and properly test them.

Disconnect the main connector on the module and read the ground wire in the connector to chassis ground to insure that it is not high resistance. The module can have all the power in the world but if the ground is crappy, it will not function properly.

That's where I would start.

Bill

 

I have a late 98, its a front mounted EBTCM. The battery is new and the correct size and amp ratings but I will be pulling it to start checking grounds. Also going to start with the chassis ground plugs in the engine bay. Im going to be slow and thorough with this, from reading all the advise it seems grounding issues are the more common thread. Thanks everyone for the help, Ill give an update after going thru the grounding system.

 

I would NOT remove the Brake Pressure Modularter Valve portin of the unit. Just the EBTCM. Be careful with the ground lug on the motor. HOLD the nut that is against the motor housing and DO NOT let it turn when you remove the nut that secures the ground wire. Use PB Blaster and let it soak befoore you remove it.

Measure the wire off that motor to a good known chassis ground to see it the resistance to the actual ground (G-101).

BC

 

Here's my drive to the store today. I haven't had a chance to check any grounds yet, weathers been bad. I did notice the grounds look a bit corroded.

 

I have an update and I thought it out and came up with a very simple fix. It was a grounding issue and here's the simplest of fixes. Start on the drivers side ground point for the engine ground strap. Remove and clean it with a wire brush. With a good quality wire, gauge 12, with good connections, heat shrank sealed with ring connectors, make a circuit moving up the frame rail to the next ground point behind the drivers headlight. Loop another section of wire to the passenger side ground point directly across, cleaning as you go and ending with the battery ground under the battery tray. This simple circuit loop solved 99% of all the issues I had. Use good wire, 12 gauge or better. Use good connectors, I stripped the plastic off of the crimps and sealed them with marine grade heat shrink. I went under the radiator cover and zip tied the loop to the fan shroud with drilled small holes in the plastic.