puzzeled by brake switch status

Caprice and GM-related general tech topics. Questions & topics on vehicle tuning, HP Tuners use, etc.....
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rcodea1
Posts: 22
Joined: Fri Jun 07, 2019 5:58 pm

puzzeled by brake switch status

Post by rcodea1 » Thu Aug 29, 2019 3:55 pm

looking for some help here....still.....

I am trying to get this brake pedal position switch to work properly. Basically, the current setup works when the KOEO, but once the engine starts, I get nothing to register. It remains in the same state after start as it was just prior to start. log is attached.

Also attached are the wiring diagrams for the 2014 Caprice PPV, trying to understand what I am doing wrong, or if the ECM changes source data to output the state of the brake pedal.

At present, I have wired the dual brake switch (NO and NC switch) so that the NC portion connects the X1 pin 9 to ground. Once the brake is applied, that circuit is opened. With and without a 1K resistor, this wiring works fine and registers the state change on the log. Once the engine is running, this state does not change...whether I apply ground or 12V....it does not change. This essentially mimics the second wiring diagram.

My harness also does not have wires for a brake position sensor, nor does the brake pedal. This is the first photo. I can make something to mimic this wiring, but a perminent install will be challenging. My idea here would be to use the NC switch to apply a single resistanced 5v signal to pin 26. But doing so would mean eliminating the current setup.

My questions:
1) what does the e38 do with this data when in operation? if it thinks the brake is always on or off, will that change the operation somehow?
2) should I even make an issue of this? Afterall, the TCC is working as advertised.
3) does the e38 computer change source data for the brake position once the engine starts?
4) can/should I repin my harness to reflect a false brake position switch using a singal reistance and 5v signal?

thanks for the time!

~Ryan
Charleston, SC
Attachments
ECM wiring.png
ECM wiring.png (32.55 KiB) Viewed 15971 times
BCM wiring.png
BCM wiring.png (28.56 KiB) Viewed 15971 times
~Ryan
Charleston, SC

smwalker
Posts: 2042
Joined: Mon Jul 29, 2013 6:44 am
Location: Azusa,CA

Re: puzzeled by brake switch status

Post by smwalker » Thu Aug 29, 2019 7:32 pm

Have you done the calibration with a scan tool?

CALIBRATION
Do not apply the brake pedal during the brake pedal position sensor calibration procedure. Any movement of the brake pedal during this procedure will cause the calibration procedure to fail. If this occurs, the brake pedal position sensor calibration must be repeated.
Brake pedal position sensor calibration must be performed after the brake pedal position sensor, body control module (BCM), engine control module (ECM), or hybrid powertrain control module have been serviced. The calibration procedure will set the brake pedal position sensor home value. This value is used by the BCM and ECM/HPCM to determine the action of the driver applying the brake system and to provide this information to the vehicle subsystems via serial data.
Steve Walker
Azusa, CA
'11 PPV 9C3 Huron White

rcodea1
Posts: 22
Joined: Fri Jun 07, 2019 5:58 pm

Re: puzzeled by brake switch status

Post by rcodea1 » Thu Aug 29, 2019 8:08 pm

no, being that this is a swap into a c10, there is no BCM, neither is there a brake pedal position sensor...only a on/off switch.
~Ryan
Charleston, SC

Pursuit
Administration Staff
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Joined: Tue Apr 23, 2013 8:39 pm
Location: Omaha, NE area

Re: puzzeled by brake switch status

Post by Pursuit » Thu Aug 29, 2019 11:11 pm

Even though you probably don't have ABS on the C10 could the ABS system, internally, be looking for the brake position signal? Is the ECM looking for the ABS? Just guessing here...

Maurice
Maurice Sheil

mhsheil@gmail.com

2011 Caprice Phantom Black 9C3
2012 Impala 9C1
1995 9C1 Caprice
1996 GMC Sierra C1500
1974 SJ Grand Prix 455 well optioned with factory moon roof

rcodea1
Posts: 22
Joined: Fri Jun 07, 2019 5:58 pm

Re: puzzeled by brake switch status

Post by rcodea1 » Fri Aug 30, 2019 2:39 am

Pursuit wrote:
Thu Aug 29, 2019 11:11 pm
Even though you probably don't have ABS on the C10 could the ABS system, internally, be looking for the brake position signal? Is the ECM looking for the ABS? Just guessing here...

Maurice
possibly, but if so, i have no way of spoofing the PCM/ECU to make that happen.

driving it longer distances today seem to show its working fine, though the status is just throwing me off.

i was recomended to try updating to the newer hptuners 4.4.4 from 4.4.2.....i'll try that first and see what happens.
~Ryan
Charleston, SC

rcodea1
Posts: 22
Joined: Fri Jun 07, 2019 5:58 pm

Re: puzzeled by brake switch status

Post by rcodea1 » Sun Sep 01, 2019 9:54 pm

neg, 4.4.4 didnt fix it. i'll have to take a video with my phone as the log doesnt show it
~Ryan
Charleston, SC

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