Clutch and Brake Causing Engine to Die

Ok, I have a weird one that I can't quite seem to get to the bottom of. It took me a while to figure out the secret combination that was making this happen, so here it goes... Note: 2010 4.0L M/T

My battery light came on the other day and the engine began randomly shutting down every now and then when I slow down or come to a stop. I checked some of the obvious things like the battery connections and connections to the alternator. All seemed well. Good solid battery connections and I even took it to my local auto parts store and they told me battery was still great along with the alternator. No clue why the battery light would be on. It also seemed very intermittent.

Then I just happened to be playing with things in the driveway and noticed that if I step on the brake, the battery light goes out. Furthermore, if I first push in the clutch, then push in the brake (like, say, you are coming to a stop or slowing down), the battery light still goes out but the engine RPMs dip quickly and sometimes enough for the engine to completely die. The engine will start back up right away with no problem, but it can be a bit annoying coasting through a turn at a stop light to quickly lose power steering then get it back quickly when you restart the engine. I am now really suspicious of the battery light, since it is pretty obvious the battery is actually getting charged with the number of times I have restarted this thing in the last few days.

I have tried working through the wiring diagrams to find a link between the clutch and brake switches to no avail. First thought was loose connector or a loose ground, but I haven't found anything yet in my digging.

Any thoughts on what else to check? What would cause the engine RPMs to dip only when you push in the clutch, then tap the brakes?

I hope I am missing something simple so I don't have to pay the local dealer's ridiculous diagnostics fees... but it isn't looking good

 

Nothing like diagnosing electrical problems eh? I had an VW GLI VR6 that would die in similar scenarios like you are describing. It turned out to be a combination of a bad battery and connection. The battery was cracked and leaking around the negative terminal. It is a weird scenario because my VW idle fine and run fine at speed but as soon as engine load dropped to idle speed it would die. I would suggest checking your ground connections. Wherever they are. Lol.

 

What happens if you coast in neutral and press on the brake?

 

The 1st gen 5VZFE had a throttle position sensor that could go bad, and would screw up the idle, and/or other things. Low idle means poor battery charging, and, well, low idle might cause it to die. Not sure if the 1GRE has the same system, haven't needed to look into it yet. How does it idle when parked?

Edit: also check vacuum lines.

 

Your guess is as good as mine, but I am pretty sure the battery light indicates low voltage which leads me to believe it would be a poor connection.

 

If your RPMs drop too low, the alternator may not be spinning fast enough for adequate charge, and the light would go on. When bench tested, this factor would not be present. Other systems can influence these symptoms.

So, again, is your idle normal when parked?

 

Only the battery light goes out, engine doesn't dip unless I also have the clutch in.

When parked, no issues (so long as I don't have the clutch in and push the brake). Idles around 800-900 when warmed up. If I just touch the brake when parked, battery light goes out with no other issues.
Vacuum lines... urgh. Not a bad thought, but doesn't explain the battery light?

 

It might be worth having the alternator bench tested just to completely rule it out... I may go do that either way.

 

This is an odd one, the kind of thing I like working on. I get pissed, cuss, throw things but, I enjoy the challenge.

I would first disable the circuits that are causing the problems. Put a temporary bypass in for the clutch switch so you can start it. Pull the fuse that controls the brake lights. Test, if the problems are gone, start reconnecting things one at a time. It would be easy to put the fuse back in, then disconnect the tail lights leaving the 3rd brake light connected. If the problem came back you probably have a short in the 3rd brake light. If not, plug in tail lights one at at time test, then the other and test.

Just because the connections look good doesn’t always mean they are. If you have a multimeter, disconnect the battery, check continuity between the negative terminal and frame, block, alternator, all over making sure there isn’t something that isn’t getting good ground. You could also try googling coolant electrolysis test and check your coolant.

That’ll give you a few things to try, good luck. Let us all know your final outcome.

 

Looks like fuse 4 is for Stop lights, high mounted stop light, vehicle stability control system, anti- lock brake system, shift lock system, multiport fuel injection system/ sequential multiport fuel injection system, towing converter. So it might not start at all with that fuse out.

Silly you can’t pull one fuse for brake lights or tail lights. So to test the 3rd brake light, you have to disconnect the tail lights.

 

Just for giggles, do you have a trailer connector, and is it clean?

 

Ok... fingers crossed I may have fixed it this evening. Time will tell the next couple days if it stays fixed or if the little gremlins return.

For my sanity, I took the alternator out and had it tested independent of everything else. Perfect score, no issues (couldn't be that easy... could it?). After re-installing the alternator and reconnecting the battery, I tried two different things. In hindsight, I did all this, then tested things so I am not quite sure which fixed it. First, I took a multi-meter tracing multiple ground points (mainly the easy access ones near the battery and under the left kick panel (I think labeled EB and IA respectively in the wiring diagrams). Both looked good, but then I tried taking a wrench to both and both actually did seem a tad loose. Not enough to wiggle the wires around, but enough that they maybe might not be making great contact if some corrosion or something was taking place. If I trace them out in the wiring diagram, the body ECU does have a key ground on IA and the engine ECU definitely needs EA. Could be causing the wonky shutdowns? Finally, I ended up doing what Waasheem suggested and started pulling fuses, but I only got to one. I pulled the Stop fuse first since the brake had something to do with it and sure enough... no issues and no battery light. Replace fuse, all still good.

So. In case someone else runs into this weird one, I recommend trying these 3 easy things first before you begin to beat your head too hard against the nearest vertical surface (on top of having your battery and alternator checked):
1) Disconnect the battery and leave it for a while. Why? It likely reset the ECU. If a bad ground or something else put it into some weird mode or it learned a bad habit due to the gremlins, this may have helped clear things up. I left mine overnight (since I was waiting to take the alternator in to be tested the next day), but some folks seem to say between 10 and 20 minutes based on other similar forum posts.
2) Ground wire connections. More importantly, don't trust the multimeter 100%. Make it easy on yourself and just try tightening up a few you can see. This may have again been causing ECU issues (thinking mainly the IA one under the left kick panel) since it seems the most interconnected to the brake and clutch circuits (ish). Could explain why actuating a brake or clutch switch would have changed a ground path.
3) Fuse jiggle. Pull the Stop fuse (or any of what you could consider to be the offending circuit) and then put it back in. It might have some corrosion on it or something... who knows, easy test.

I will post back if I have any more issues, but here's to good luck this solved it. Many thanks folks.

 

This is when the meter says good continuity but, a wire that’s broken leaving one strand connected will test good continuity.

If you look at the battery ground wire, there’s a pigtail smaller wire that connects to sheet metal. If you remove the bolt attached to the sheet metal, it’s painted under the lug. So electricity is going pigtail, terminal, bolt, bolt hole threads, sheet metal. Not ideal, if the bolt threads get rusty, worse.

I’ve read of a few people who broke that bolt so if you’re going to mess with it, I’d suggest penetrant and patience.