Let's talk about RAP - retained accessory power

[Elektrishun]

Got a call from my wife yesterday that her car wouldn't start. She went to a 2 hour appointment and afterwards tried to start the car without success. Brought the NOCO booster and tried it for the first time. Got it started with some effort.

Source of the problem is believed to be the radio not shutting off after opening the door. Maybe it was turned down low enough that she didn't realize it was still on?

According to the information I found here's how it should work:

After questioning my wife about this she stated that this has happened intermittently before. She will then manually turn the radio OFF before exiting.

So making sure the radio is OFF before exiting is the simple fix. But if I understand the info above shouldn't the BCM have shut-off the radio within 10 minutes or after sensing the battery voltage had dropped to whatever predetermined level? If the BCM doesn't shut the radio OFF for any of those reasons then maybe it's not receiving a signal. In that case would I be looking for a broken wire, maybe a bad ground, that is creating the intermittent issue?

Found this video but his RAP issue is a little more straight forward because it doesn't appear to be intermittent:

RAP Relay

Anyone deal with an intermittent RAP issue before?

 

[David]

Me thinks the battery is on its last legs if the radio will drain it enough to prevent the car from starting. Obviously that doesn't mean the RAP is working correctly.

 

[ChazzC]

My wife’s 2019 Trax died overnight because the shift lever wasn’t quite all the way into Park, which allowed radio, lights, etc. to keep going. Since this was the first car without a key, we couldn’t get in so I could pop the hood. (I now know where the hidden key is inside the fob - and why there’s a keyed lock on the driver’s door).

 

[Elektrishun]

Me thinks the battery is on its last legs if the radio will drain it enough to prevent the car from starting. Obviously that doesn't mean the RAP is working correctly.

Yes

2 hours shouldn't have discharged it that much.

EDIT - but the BCM should have shut the power off in 10 minutes or before the battery voltage dropped too low.

 

[David]

Yes

2 hours shouldn't have discharged it that much.

EDIT - but the BCM should have shut the power off in 10 minutes or before the battery voltage dropped too low.

I did a quick google search and found this generic article from Autozone on resetting the BCM to sort out strange behaviour.

How To Reset the Body Control Module

Learn how to reset your vehicle's Body Control Module (BCM) to fix various electrical issues. Follow simple steps to restore factory settings and improve performance.

www.autozone.com

 

[Elektrishun]

RAP Modes Schematic 2008 Chevy Uplander

Maybe I am not looking at this correctly... but if the vehicle is shut OFF then the RAP relay should be energized which signals the BCM that the RAP relay is energized? If the signal is not sent that the RAP relay is energized then maybe the BCM doesn't acknowledge the door opening, 10 minute countdown timer, battery draining...???

Maybe an intermittent RAP relay issue?

 

[David]

I'd investigate the relay first.

 

[Elektrishun]

My wife’s 2019 Trax died overnight because the shift lever wasn’t quite all the way into Park, which allowed radio, lights, etc. to keep going. Since this was the first car without a key, we couldn’t get in so I could pop the hood. (I now know where the hidden key is inside the fob - and why there’s a keyed lock on the driver’s door).

My wife's FOB wasn't working consistently. The plastic cover was cracked and I think it wasn't allowing good contact when she pressed the buttons. Got a new plastic cover and replaced the old. Sometimes when she puts the FOB in her pocket and bends over the car horn goes off.

I told her that is a safety feature. If you are ever attacked just bend over.

 

[Elektrishun]

Well, after numerous attempts I can't re-create the scenario where the radio stays ON after opening the driver's side door. It just keeps working the way it should. This despite being told that the radio staying ON has happened a few times in the recent past. For now it will remain a mystery glitch.

 

[Elektrishun]

@David

No signs of starting issues after the initial incident mentioned above but because we had a road trip to Edmonton coming up I decided to check the battery date. It was going on 5 1/2 years. Decided it was time to replace it. The age of the battery might have contributed to the events that resulted in the vehicle failing to start.

 

[Dan Dubeau]

I had similar phantom electrical issues with my truck a few years ago. The CD player would go into this loop where it would constantly try to take in/eject a cd. Even when the power was off. Of course it would drain the battery over night. This went on for a few weeks, and I'd just unclamp the negative terminal. Then I started having all kinds of other electrical issues, like going into limp mode while driving, and eventually the truck was just non responsive. Had it towed to the dealer (sign of defeat 🙁 )Issue turned out to be massive amounts of corrosion in the PCM/BCM. 2k later......issues all solved, and the truck is fine to this day (aside from 15 years of rust and body rot).

Reading about this after the fact, many people had luck cleaning them themselves, so that might be something to think about if you're curious. Dead/dying batteries can cause things to act up with low voltage too, but I don't really have the knowledge or experience to delve into that deeper. Electronics at that level is beyond my understanding.

 

[Mike R]

Something else to consider - different car type but similar issue.
I had a 2013 Mazda CX-5 do this, its fairly common on them, push button start. The switch that detects "park" gets old and a little rubber snubber compression sets enough that you think you turned off the car completely but you only turned off the ignition, as its still in some form of drive mode, and that would kill the battery.