My wife'e Vette (2001 Convertible / 46856 miles) has been having this issue now for about 6 weeks. I get the dreaded TCS28 code and when I access it I get sub code 1214. I try to clear the code but it simply won't let me do it. So I end up having to only clear the ABS Active Handling displayed warning and I drive the car maybe five or ten miles. I shut the car off and turn it back on and the codes disappear. Now before someone says the ECBM is faulty I had it rebuilt about four years ago by ABS Fixer and it has performed flawlessly.
So I checked battery voltages and my battery was only reading between 12.1 and 12.5 after sitting overnight or for two or three days. I drove the car and the battery voltage on the DIC never got above 13.3. I performed a load test on the battery and it dropped to 11.8 and recovered to 12.2. I figured that it was possible the battery was failing (NAPA Premium AGM) after only 3 years. So I purchased a new Odyssey Extreme AGM and it seemed to work fine for about 10 days. I drove the car the first day and it was showing 14.3 volts on the DIC and then a couple of days later it was showing 13.8 but still no codes that is until today. The car hasn't been driven much other than to the store and back five or six times which is about 5 miles round trip and possibly two or three 20 mile trips and today the Active Handling / Service ABS System TCS28 code reappeared when I first started the engine. I checked the battery when I got home and the battery was only at 13.3. I back probed the alternator to see if it was putting out enough and according to the meter it was putting out 12.9 and surged only to 13.6. No matter how high I revved the engine I couldn't get the alternator to go past 13.6 and the battery higher than 13.4.
I am now wondering if it is possible I may have an intermittent short in the alternator or possibly a failing diode or regulator which is not allowing to the battery to fully charge and stay charged. As I said the codes clear themselves after the car has run for at least twenty or so minutes which in reality is enough to bring the battery back to a reasonable voltage rate. So if it isn't the alternator or the grounds that I have cleaned as well I'm sort of lost. I know it could be many things but I can't help but think it is something very simple. Can someone please shed some light on this problem for me?

 

Moved to C5 Tech.

 

You really don’t look at voltage to check the output of an alternator…you would want to look at current flow with an ammeter. I would do a voltage drop check of the positive and negative sides of the charging circuit !!…if you need guidance let us know !!

 

The DTC C1214 is very often caused by a relay gone bad in the EBCTM or bad soldering on the EBCTM circuit board
With some soldeering skills it is usually an easy job to replace this relay feeding the ABS solonoids
How to is shown in this