Emergency Brake light + Red Battery light come on at odd rare intervals

Varak · 12-02-2012, 09:51 PM

This has happened three times in the past 6 months, and I have no idea what is causing it.

Each time, the brake light (emergency brake) and the red battery light (one that comes on when 12V battery isn't getting charged) come on together.

The emergency brake is not engaged and the car otherwise acts normally.

In each case, keying off/on caused the problem to go away. I had no engine codes set.

It isn't causing issues, but I'm wondering if this is a sign of a pending problem or if it is simply an electrical blip of some kind.

Any ideas?

gilbertguy · 12-02-2012, 10:08 PM

Is your IMA battery still on life support from the grid charger? No engine codes you say but what about IMA codes???

Varak · 12-02-2012, 11:20 PM

At the time, there were no IMA lights/codes. I had a P1449 yesterday and did a grid charge last night so the battery had been topped off.

I'm guessing it some type of electrical issue, but not sure where to look since it is so rare and random.

I'm getting P1449s every 200 miles these days.

eq1 · 12-03-2012, 02:14 AM

It could be, or likely is, related to a weak HV battery. Something to do with low pack voltage and triggering the DC-DC converter to shutdown... I've seen it a handful of times, mostly when pushing assist aggressively, but not exclusively...

EDC · 12-03-2012, 09:32 PM

check your ground straps-engine to frame;&to trany. also check for a bad electrical(not just mechanicly tight) 12volt battery terminal connections. and yes it can be an HV battery death starting.
ed

**Eli** · 12-04-2012, 06:39 AM

It's normal for the brake light to come on with the DC-DC light. It's tied together this way if you look at the wiring diagram. Why? Who knows, it's just the way it is.

The brake light can come on without the DC-DC light coming on, but not the other way around. Anyway...

I'm betting it's not "random intervals". It probably happens after a hard acceleration in 2nd or 3rd gear; the full assist causes IMA battery voltage to dip low, triggering the DC-DC to be shut down.

If it truly is happening randomly when nothing is going on, your battery is even weaker than the above would indicate.

eq1 · 12-05-2012, 02:36 AM

fyi, I just read another thread that mentioned the battery and brake light, along with a couple other quirks, such as speedometer issues, that indicate a bad/loose #4 fuse...

**Rush** · 12-05-2012, 02:59 AM

Quote:

Originally Posted by Eli

I'm betting it's not "random intervals". It probably happens after a hard acceleration in 2nd or 3rd gear; the full assist causes IMA battery voltage to dip low, triggering the DC-DC to be shut down.

Eli has it - I'll bet. What happens is that the motor revs over 4k and the DC/DC converter turns off for about 45-60 seconds. The emergency brake light and the battery light come on. It is perfectly normal for that to happen when the IMA is disconnected.

When I was running with out the IMA, I'd do it all the time. And everytime I did it, I'd count the seconds and pray that I hadn't broken something.

Get a BBB and it will go away

eq1 · 12-05-2012, 04:21 AM

Quote:

Originally Posted by Rush

Eli has it - I'll bet. What happens is that the motor revs over 4k and the DC/DC converter turns off for about 45-60 seconds. The emergency brake light and the battery light come on....

The brake and batt lights due to high revving w/ IMA switch off versus due to low pack and/or stick voltages are two different things. Normally the IMA throttles back current to prevent pack voltages from dropping below 125, but it can take some moments to do that. With a weak pack the issue is more acute - pack voltage drops below 125 for more than just a blip and the DC-DC converter shuts down, the batt light and brake light come on. It seems to take a little more than just turning the key off then back on to reset the DC-DC, as I've tried that but to no avail... It seems to take a bit of time...

fishtrap · 12-16-2012, 01:26 PM

What I found on number 4 was that the fuse tested good and contacts looked good, but it didn't work! Went to an auto repair shot and a marine electrician and they both told me that every now and then they come across a fuse that does this. They explained that a fuse may hold voltage and not amperage.
I had pulled every fuse 2times but had not replaced any. I worked on this car for 12 days trying to find the problem.
Also what was said about the engine revving over 4k and the lights coming on is true. I had that happen and the recreated it twice.
Don't know if that helps, but I plan on changing that fuse ever month or so to be safe.