Brake signal to e38

[87skier]

I know this has been covered around here, but I'm having trouble with the brake signal in my 2013 e38 ecm.

I have it wired so that the ecm sees:
12v - Brakes not applied
0v - Brakes applied

With the engine OFF, the ecm displays the appropriate status (yes/no). As soon as I start the engine, the brake status is permanently NO. I verified that nothing changes after the engine has started.
The computer has a code for the brake signal P057C or P057B. After I shut the engine off, the status appears correctly.

I saw some mention to the 2012-2013 e38's using a pedal position switch instead of a simple on/off switch. Is this true?

Any help is appreciated!

PS: the engine, ecm, and transmission are all from the same vehicle. No major reflash's have been done, just disabling stuff to make the engine run (vats, starter checks, etc...)

[Jon S.]

I know this has been covered around here, but I'm having trouble with the brake signal in my 2013 e38 ecm.

I have it wired so that the ecm sees:
12v - Brakes not applied
0v - Brakes applied

That is the brake logic used by the LSx Gen 3 controllers (P01 / P59).

The Gen 4 controllers (your E38) use the opposite logic:
- 0V when brakes not applied
- 12V when brakes are applied

This brake signal needs to be wired to both the ECM and TCM (if applicable).

[DSteck]

Some of the TCMs just rely on a CAN signal for the brake. Hit or miss it seems.

Newer E38s do use the pedal position sensor, but they also still expect the 12V brake apply on C1 9. Having said that, there is also a CAN message for the brake apply which may be what the ECM is wanting to see.

[87skier]

I believe it is wired up correctly now. It is reported correctly with the engine off. I may have switched around which way it is wired up when I typed up my post.

Signal goes to both ecm/tcm. I checked when I had the harness apart.

I suppose I could see the computer reporting brake signal form the wire then once the engine is running relying on both CAN and wire signals. I was thinking that the brake signal over CAN was broadcast by the ecm only. In this case, there must have been a another brake signal going to the BCM to communicate with the ECM.
This could be some sort of vehicle safety function so that it can't be started without the brake pedal being depressed.

[DSteck]

The brake signal originates from the BCM as far as CAN is concerned.

[Gihan]

I am having a very similar issue with my brake signal on an LS-swapped Land Rover Defender (2011 Corvette LS3 [E38] & 2010 Camaro 6L80E [T43] ). I have wired the brake signal using a 5-pin relay such that it has ground when the pedal is pressed & 12V at all other times. The brake state works fine when the engine is off, but when running, it doesn't change. I believe this is the reason my torque converter seems to stay locked up when I shift into either drive or reverse, even when I step on the brakes. Appreciate if someone can point me in the right direction. Thanks.

[AK427Cobra]

Gihan,
I have an L99 with E38 and 6L80E (T43) 2012 Camaro tunes for both. I have one signal for TCCLockup from brake switch. 0V when brake is off, 12V when brake applied. Looks like your set up is reversed and sending 12V when brake is OFF? I'm fairly sure it needs to be opposite in your setup?

[blindsquirrel]

Much easier than using a relay: https://en.wikipedia.org/wiki/Pull-up_resistor

In electronic logic circuits, a pull-up resistor or pull-down resistor is a resistor used to ensure a known state for a signal. It is typically used in combination with components such as switches and transistors, which physically interrupt the connection of subsequent components to ground or to VCC. When the switch is closed, it creates a direct connection to ground or VCC, but when the switch is open, the rest of the circuit would be left floating (i.e., it would have an indeterminate voltage). For a switch that connects to ground, a pull-up resistor ensures a well-defined voltage (i.e. VCC, or logical high) across the remainder of the circuit when the switch is open. Conversely, for a switch that connects to VCC, a pull-down resistor ensures a well-defined ground voltage (i.e. logical low) when the switch is open.

[afraptor22]

Did anyone find a solution to this? I have the same problem using an E38 with a 2010 truck OS. Yes, I know the logic is inverted between gen3 and Gen4. My setup used to work correctly when I was using a 2008 E38, but I bricked that box and replaced it with the 2010, also to match the TECHM in my 6L90.

[LaTechGTO]

Bringing this back... I am battling with a '68 Camaro with a 2013 E38 / T42 combo.

Just like the OP, everything functions as normal when the key is on and the engine is off. I verified the ECM and TCM brake signal pinouts to ensure both are happy (it will act the same when only the ECM is fed the brake signal. Once the engine is started, it seems to fail to the last position (for instance, if the brake is on, it will stay showing on, and if the brake is off, it will stay showing off) before cranking and won't change at all after the engine is started.

Any help would be greatly appreciated!

[towman79]

Same here. Been driving me crazy reading all the misinformation on the net.
09 LY6 6L90 e38

[towman79]

Someone on a FB group gave me instructions for using a relay to supply 12v while brake applied and ground with a 1k resistor while off. Apparently the ecm wants a ground signal with the resistance of a light bulb while brakes not applied. I tried it using an 1156 bulb instead of the resistor but it didn't work. I ordered some resistors now so I'll update when I get them. Has this method worked for anyone else who was originally having this issue?

[LaTechGTO]

Someone on a FB group gave me instructions for using a relay to supply 12v while brake applied and ground with a 1k resistor while off. Apparently the ecm wants a ground signal with the resistance of a light bulb while brakes not applied. I tried it using an 1156 bulb instead of the resistor but it didn't work. I ordered some resistors now so I'll update when I get them. Has this method worked for anyone else who was originally having this issue?

I tried that, and it didn?t work.I?ve read it?s worked for some people though.

[towman79]

Yeah, i just finished wiring it up and it didn't work.

[Crash41301]

Bump? Exact same problem with a l99 + 6l80e from a 2015 camaro. Works just fine when the engine is off. When I start it VCM scanner shows that PCM doesnt see the brake change. I've also validated the exact same voltages occur going to the PCM engine running or not with multi-meter. Engine swap shifts hard AF during normal driving. I'm assuming this is why and would like to fix it as its pretty annoying.

[LaTechGTO]

Never got it to work, unfortunately

[Crash41301]

Never got it to work, unfortunately

Well thats disappointing. Do you just drive around with a locked up TCC all the time?

[LaTechGTO]

Well thats disappointing. Do you just drive around with a locked up TCC all the time?

I’m not sure what the owner does. He is just a neighbor and asked me to help. I’ve seen him drive the car quite a bit so I suspect he is just dealing with it.

[Jpat83]

Did anyone ever come up with a solution for this? I have a 2013 corvette E38 in a rx7 swap. Same issue reported here- when the key is on, engine off, scanner shows brake signal works perfectly. Start the car and it no longer switches. It looks like it does stay with whatever state it was in during start up- if i hold the brake on the scanner shows brake pedal is pressed even after release. If the brake is not on it shows pedal is not pressed even when i press it.

[Jpat83]

just thinking this through- is it possible since the signal is coming from the BCM in the original car that the ECM is looking for 12V and not the 13-14V that would be coming from a brake signal in a swap car because of the alternator? could that be why it works with the engine off?