sebdavid

I'm looking everywhere but I can't find the info: I swear I read somewhere that when electronic aids stop working on a C5 (for example faulty wheel speed sensor), you don't just lose ABS, TCS and all other systems, but the electronic Dynamic Rear Proportioning stops working and brake bias goes to the rear. Is this correct?

For some reason my electronics are giving up the ghost 2 laps into every session (but not on the road) and now I'm eating rear brake pads like crazy and the brakes feel really weird.

I wouldn't mind running without the aids for a while if it weren't for that issue, if it is indeed an issue. Can anyone confirm? And can anyone tell me why the system would "default" to more rear bias when electronics stop working? Seems counter-intuitive to me...

froggy47

mgarfias

Yep. The dynamic proportioning works by taking brake away from the back end via the ABS module. I had my car nearly swap ends a few times when the ABS was out.

trackboss

I belive that is only on the later C5's. My '99 FRC I'm pretty sure is all mechanical/hydraulic in terms of bias.

urtoslo

Don't know about electronic brake bias.

Had ABS/TCS die in a race and the rear took work to keep from locking up. The Hoosiers in the rear were old and when the rear got light under heavy braking, it took a good deal of pedal modulation to not lock them up.

sebdavid

Yes, electronic proportioning only started in 2001. I have an '03 C5Z.

Glad to see I'm not crazy. Still don't understand why the system would be set up this way though...

It does it less now that I've changed pads, but at one point it felt like the rear started braking first, then overheated (pedal got long) and gave a lot less braking power, at which point the fronts started to bite and the pedal came back suddenly. I changed the front pads to a different compound and it does it less but it cost me a flat-spotted front tire.

And initial braking application when you have to brake with the car slightly loaded in one direction is interesting.

RX-Ben

My first TTs in my C5 were w/o ABS since I had the common problem in '01+ modules (which was an easy fix for $50). The car behaved fine (though clearly not as good as with ABS) and I did not have any unusual pad wear.
I have had a number of intermittent problems and they have all revolved around the sensor or the plugs. I replaced some of my ABS plugs with Weatherpack connectors. The other problem may be the wiring coming out of the sensor/hub. I had the sensor wires crack and break off, using the SKS race bearings, with all of 3-4 track days on them. I have only had that problem once.

geerookie

Get the DTC codes and I can give you a better idea of what is happening. Any hiccup with ABS or TCS related to wheel speed sensors or the EBCM will set a code and requires 50 ignition cycles of no fault to clear.

sebdavid

Funny enough, even with the christmas tree lit up in the dashboard warning me I'm actually driving on my own (ABS, TCS and warnings in the DIC), I'm not getting any C (Current) codes, just H (Historic) ones. But I'm sure they're related and they have to do with the LR corner, and/or steering:

C1227 LR excessive wheel speed variation
C1234 LR wheel speed circ open or shorted
C1283 excessive time to center steering

What's weird is it only happens after 1-2 laps into a track session and I can't reproduce it on the street. I've triggered TCS on the street and it worked. Driving down to NJ I did get the issue on the highway, and it didn't go away until the next morning when it went away only to come back on track, and now it only triggers on track. Maybe a loose connection? Didn't find any when looking at the LR corner, but I'm no expert.

I do have a power steering fluid leak though. Steering rack was replaced at dealership last year...

Wasserott

I had bad sensor and just pulled fuses (for 2 years) and pressed on. Yes, no ABS but with areo i had good traction to not have a terrible time w/out it in the rear. Problem was front lockup only. But no weird bias issues.

2002 Z06

No excessive pad wear.

sebdavid

No excessive rear pad wear?

RX-Ben

I had the same issue. It was heat. Check the wires. If they look good, replace the plugs.
I had the steering code before, but only when I got an alignment and the shop didn't center the wheel (which I later did).

geerookie

The excessive speed would be from a lite wheel and getting wheel spin, I wouldn't worry about that one.

The open short is more likely from a bad connection or possibly a failing hub sensor or bad rear ground. There are more connections than just at the hub. Trace the wire and you will find the second connector.
Also remove the ground wire on the frame, clean the connection and reconnect.

The steering centering code is probably because the steering wheel is not connected to the rack centered or while the wheel was disconnected from the rack it got moved and reconnected wrong.
The only way to fix this without removing the SWPS is to measure the voltage coming from pin 5 (LT GRN) and/or pin 6 (LT BLU) wires out of the SWPS. Measure from ground to each pin. When the voltages are equal, ~ 2.5Vdc then the sensor thinks it is centered. The range should be from about .15Vdc to 4.85Vdc.


The dynamic rear proportioning (DRP) is a control system that replaces the hydraulic proportioning function of the mechanical proportioning valve in the base brake system. The DRP control system is part of the operation software in the EBCM. The DRP uses active control with existing ABS in order to regulate the vehicle's rear brake pressure.

The red brake warning indicator is illuminated when the dynamic rear proportioning function is disabled.

sebdavid

That's a lot of great info, thanks! The car is at the dealership now to get the steering rack looked at (it's leaking and still under warranty from a September replacement). I guess they'll find it, I couldn't look at it as I'm leaving for France now.

From your last paragraph, it seems like rear proportioning should still be working. But then why am I going through rear pads faster? I remember this happening to me also when my EBCM was faulty a year and a half ago or so.

froggy47

Do you use Competition Mode? That'll toast the rears.

2MCHPWR

this might be a bigger issue:

C1234 LR wheel speed circ open or shorted

it was for me.
At first I replaced the hub but still got the DTC.
So I traced the wire back and found it leaning against the exahust and burned/melted together causing the fault. The resulting spin at the Glen going 137 mph almost had me in the wall on the main straight braking for turn 1. The video of it is insane. My car is a 1999 but I think the computer is a 2003 but not sure if it has the 01+ brake system (many previous owners). But once I had that code (and I didn't see it because was not looking at my dash), the rears locked up like they were on ice and spun me hard.

sebdavid

Of course not. Strap in, turn coolers on, turn nannies off, proceed to pit-out. I may have one of the rear calipers due for a rebuild but not both and the wear is increased on both sides.

sebdavid

I read about your issue and saw the video, yikes! I don't know if that wire is always routed so close to the exhaust, I'll have the dealer trace it back. It could be that as it seems to be heat-related. The rears aren't really locking up as aggressively as ou mention (maybe you were using more aggressive pads than I am), it's manageable although it feels weird.

drivinhard

easy to tell, the early cars on the pump the lines go in from the side (and the unit is bigger)

on the later cars the lines go in on the top and the unit is a little smaller

yakisoba

I've had wheel speed sensor errors from small things. Like once a dirt wasp built a nest on the sensor wires. That tripped the code and turned traction control off. When I found and broke the nest (and the now cooked wasps) off, it cleared up.