BCM Hatch release only 5-6V - help

Reply Subscribe

Thread Tools

Search this Thread

May 18, 2026 | 10:38 AM

Vetal

Thread Starter

TECH Fanatic

iTrader: (3)

Joined: Aug 2006

Posts: 1,989

Likes: 2

From: Latvia

BCM Hatch release only 5-6V - help

Edit: currently the problem investigated as such:
I have only 4V on the BCM wire when it’s commanding relay to close with engine not running. When the engine is running, there is 1V at this pin at rest, but when I press dash button, it sends 5-6V to the relay. Sometimes it is enough to click the relay.
Why is BCM not sending 12V?

Original: Long story short, my 1999' Firebird trunk release went crazy. First it stopped opening both from dash button and key fob. Now that I started investigating, I came to the point when it started opening trunk BUT ONLY when the engine is running and transmission is in Park or Neutral.
Now even more weird, today first it worked without pressing break pedal. Now it only works while I am pressing brake pedal (and of course engine is running and transmission in Park or Neutral).
What the hell?

Last edited by Vetal; May 22, 2026 at 08:10 AM.

May 18, 2026 | 12:09 PM

gesto

TECH Regular

Joined: Sep 2008

Posts: 404

Likes: 24

From: Houston

Does it open with the key?

May 18, 2026 | 12:19 PM

Vetal

Thread Starter

TECH Fanatic

iTrader: (3)

Joined: Aug 2006

Posts: 1,989

Likes: 2

From: Latvia

Quote:

Originally Posted by gesto

Does it open with the key?

You mean physical lock cylinder? Yes.
Point is, it opens remotely as well, but in some weird combination - engine running, brake depressed...

May 19, 2026 | 08:17 AM

WhiteBird00

Ungrounded Moderator

iTrader: (4)

Joined: Nov 2003

Posts: 11,330

Likes: 346

From: Jacksonville, FL (originally from Toronto Canada)

Quote:

Originally Posted by Vetal

Long story short, my 1999' Firebird trunk release went crazy. First it stopped opening both from dash button and key fob. Now that I started investigating, I came to the point when it started opening trunk BUT ONLY when the engine is running and transmission is in Park or Neutral.

It is normal operation for the inside hatch release to only work when the ignition switch is in the RUN (engine does not need to be running) or ACCY position; or when Retained Accessory Power (RAP) is active. With an automatic transmission, it must be in Park or Neutral. With a manual transmission, the parking brake must be engaged if the ignition switch is in the RUN position. The idea is that the hatch can't be released if there is a possibility that the vehicle is moving.

Quote:

Originally Posted by Vetal

Now even more weird, today first it worked without pressing break pedal. Now it only works while I am pressing brake pedal (and of course engine is running and transmission in Park or Neutral).
What the hell?

There is no connection, either through computer logic or in the physical wiring, between the main braking system and the hatch release, so I don't know how that could possibly be involved. The hatch release is entirely controlled by the BCM and it doesn't even have a brake input signal connected to it (parking brake yes, but not main brakes). Are you sure that you didn't note symptoms that weren't actually related?

May 20, 2026 | 04:55 PM

Vetal

Thread Starter

TECH Fanatic

iTrader: (3)

Joined: Aug 2006

Posts: 1,989

Likes: 2

From: Latvia

Ok found trace of a problem: with engine not running, relay gets only 4V from BCM. I will check what happens on this wire at the BCM side. Then I will understand better why the relay only gets enough voltage with the engine running

May 21, 2026 | 06:19 PM

Vetal

Thread Starter

TECH Fanatic

iTrader: (3)

Joined: Aug 2006

Posts: 1,989

Likes: 2

From: Latvia

So the problem is, I have only 4V on the BCM when it’s commanding relay to close. When the engine is running, there is always 1V at this pin, but when I press dash button, it sends 5-6V to the relay.
why it’s not sending 12V?

Reply Subscribe

Reply Share

First
Prev
1 / 1
Next
Last