speedwaywhite

Ran with Chin at Sebring last weekend. While lapping (in Competitive mode ) the RF TPS went off line and ABS started applying brake to LF in right hand turns. Pitted ASAP, reprogrammed TPS, ran 4 more sessions with no further issues.
Anyone experienced this before?

JerryTX

Flaky TPS sensor, time to replace it. My theory: weak battery and/or brake heat shortens the life of the sensors. If it is a C6, check out LG Motorsports TPS eliminator module so that the car never goes into Active Handling mode and ruining your track sessions.

C6psi

I have had several flats on track over the years and the result is the same with the active handling intervening. If you run into this again and can't get it resolved you can disconnect the steering wheel posistion sensor and disable the TPMS all together. You will still retain ABS and traction control.

speedwaywhite

Thanks for the info, sensors only 2 years old but its a place to start. Car is 12 GS running stock OE wheels and street tires.
ABS sensor on the LF might be a suspect as well ? I should mention that earlier in that 1st of the day session I had a little off track excursion (cold tires+ dumb driver= spin) in tower turn, all 4 off but I didn't hit any curbs, grass was wet. Started acting up later in that session.

geerookie

When you say ABS sensor on the LF I assume you mean the wheel speed sensor.
That wouldn't cause the problem you had. If it was bad or intermittent you would get ABS disabled.
Your symptoms indicate TPMS sensor.
See above recommendations for bypass from LG or pull the SWPS lead.

speedwaywhite

OK, so, if it was the LF sensor that went off line the opposite wheel RF have been braking, correct?
Thanks for the reply and info.

Bill Dearborn

When the system detects a low or zero pressure tire or a sensor battery is low causing the sensor to be intermittent the TPMS system sends a signal to the EBCM which automatically puts the car in full AH mode. It also applies a 55 mph speed limit on the car in turns. It doesn't apply just one brake it applies both front brakes to slow the car. If the sensor craps out coming out of the Esses at the Glen you are close to 120 in a gradual turn and the 2 front brakes will be forcefully applied. This results in severe understeer and if you just passed somebody a good chance of them slamming into your rear as they don't expect you to slam on the brakes just as you enter the straight. I had to apologize to the M3 driver that I did this to a few years ago.

Pulling the steering sensor connector will shut down AH and leave ABS and TC operative. However, this isn't a permanent solution since the steering sensor connector and the small wires in the harness are not designed to be constantly unplugged and plugged back together. Connectors are priced on how many connection cycles can be made before they have to be replaced. Since this connector is used in a system where the normal number of life time cycles should be well less than 50 the engineer would have chosen an appropriate connector for the design with some tolerance for unusual situations. If you unplug the sensor at every track day you will quickly approach the connector end of life or maybe break some of the wires going to it.

From a reliability and overall safety standpoint it is best to move to another solution. Either the LG solution or something else. I have considered installing a toggle switch in the line but the system is a low current design and installation of a toggle switch could slightly increase circuit resistance thus reducing current flow and inducing AH errors.

Bill

Bill Dearborn

If any tire pressure sensor fails or detects a zero pressure tire the system will automatically apply both front brakes to slow the car. EMTs and other run flats have a 55 mph mas speed capability when they are operating at zero pressure and under current rules the car has to do something to slow itself to that limit. My 08 brakes in turns and lets me run as fast as I want on straights (not sure of the reason this happens given the 55 mph speed capability of the tire). However, I have to brake hard for any turn even slight ones.

C5s just warned the driver and it was up to the driver to adjust speed but I suspect the legal fallout from the Ford/Firestone underinflated tire issue ruled that out. You can't let the public make those kinds of decisions.

Bill

speedwaywhite

Thanks Bill, I was hoping to receive some input from you, as usual, you didn't disappoint! The LF was being applied intermittently, enough to chirp the LF then release and do it again. I didn't feel any RF brake at all. I not good enough yet (maybe never) to run with everything off so the LG option is good one. I will check it out before I head back to Sebring in March. Do you ever make it down to Sebring? If so, I would like to buy you a beer as partial payment for all your helpful and informative posts I read on the forum.
Cheers!

Bill Dearborn

You are welcome. I did the NCM Sebring event the last two years but I think I am done with Sebring for now.

Bill