98 Boxster 2.5 - ABS/TC lights only in morning

[cb77]

Hi all,

I have a 2.5 986, I am currently going through a list of things to get it ready for an MOT, One thing stumping me is that in the morning when I start it, I have the ABS and TC off lights on. I then drive roughly 10-20 minutes, turn car off and on and they're gone and abs and tc are working perfect. After these short drives I have turned the car off for around 1 and a half hours then come back and they've still been off,  I've tested that a few times. If I leave it for considerably longer, say 5 hours, then the lights will be back on and it needs that short drive and restart to turn them back off. 0 codes on my generic reader, no one I know has a porsche specific one though. I have checked the sensors using a multimeter and they were all okay. It has actually had a new right front sensor anyway as the hub/carrier needed replacing. Still same symptoms. 

 

It does also have alarm/door lock and maybe battery drain issues. It has had a couple battery's on it now which were fine on other cars but go flat after about 3 days stood on this. Did a drain test using a multimeter and got 0.35, is that about right? I had a theory that maybe the battery is getting drained a bit so the little drive tops it up and then solves the tc and abs issue, then letting it sit drains it back and they come on again. Sound realistic? Voltage when running is 13.5. 

Thanks,

 

 

[RFM]

035 amp is way too much, 0035 amp looks better with the system in sleep mode. So there is a consumer/control box somewhere that does not go into sleep mode or wakes up now and then. This will probably the cause of the ABS/TC problem.

[cb77]

3 hours ago, RFM said:

035 amp is way too much, 0035 amp looks better with the system in sleep mode. So there is a consumer/control box somewhere that does not go into sleep mode or wakes up now and then. This will probably the cause of the ABS/TC problem.

Thanks for the response, been giving it a go.

Radio fuse made it drop, now if I disconnect the multimeter then reconnect, as if I am reconnecting the battery I get 0.01-0.04, which seems more like it, but if I open then close the door with the multimeter still connected it now settles back down to  0.1 A and stays there for seemingly ever. It is as if it only pulls 0.01-0.04 when the car is just connected and not touched, but if I do anything to wake it up like opening the door then it never returns back to that level, staying at around 0.1A instead. I do have central locking/door lock issues too, I assumed that if they were the cause the fuse pulling would show that.

 

[cb77]

Just to add, gone out to the car just now after it being left overnight, battery fully charged, turned over quick, lights still on. Really can't figure out what it could be that changes after a short drive. Temperature?

[RFM]

I looked in to my notes regarding 996/986, ABS/TC is a combi system. Perform a throttle valve cleaning inclusief the electric connector and check the wiring, it may sound weird but the throttle body is part of the TC system and too much resistance mechanical/electrical could cause such a problem. Let us know your findings.

[mikefocke]

Isn't the normal total current draw after being shut off for 31 minutes for a '97-'99 car 17/1000 to 30/1000 amps depending on accessories?

 

Has the alternator side of the circuit been tested? I've read of the voltage regulator causing weird current draws.

[cb77]

On 6/15/2023 at 6:31 PM, RFM said:

I looked in to my notes regarding 996/986, ABS/TC is a combi system. Perform a throttle valve cleaning inclusief the electric connector and check the wiring, it may sound weird but the throttle body is part of the TC system and too much resistance mechanical/electrical could cause such a problem. Let us know your findings.

Apologies for slow reply, had clutch go on my other car so had to put this on hold. I have taken off and cleaned the throttle body and it didn't solve my problem. I am wondering what effects different batteries could have. It may have just been a lucky day but I put a smaller battery off another car and a drive as short as half a mile was enough to turn the lights off. I may just have to try and find someone nearby with a proper Porsche scan tool.