Electrical/autobox Issue On Selecting High Beam...?

[NickM91]

G'day,

So on top of my Turbo flutter noises which worsened in the hills at the snow, yesterday, on my way back to Sydney the stagea decided to play up on me a couple of times throughout the drive.

So first thing i noticed, and i do get this very occasionally so thought nothing of it, was i got a mild shudder through the drive system, sort of like the gear box is thinking about changing gear then doesn't, backing off the throttle has always cleared it, and i've read of other people having similar issues without any on going issues, but after what happened yesterday i'm beginning to wonder.

So yesterday i slowed down to round a corner at an intersection, just after i went around the bend, during light acceleration, i flicked the high beams on, and the car dropped back to what i suspect was first gear, revs shot up to 4500RPM, as i was doing maybe 40-60kph but didn't really look, but they shot up, and stayed there until i did the whole wtf, and moved it from 'D' into tiptronic mode and went up a couple of gears. I put it back into drive and continued on driving a bit puzzled by what had just happened. I didn't make the connection that it happened when i flicked the highbeams on, and continued using them as required along the drive.

About two hours later on the Hume this time doing 110kph, again, i flicked the high beams on and the car dropped back maybe 2 gears to 3rd, and the revs again shot up to 4500ish RPM, and it stayed there again until I went into tiptronic. This time i noticed that the AT transmission light came on, and possibly a few others, until i selected tip tronic. Confused again, and a bit nervous that the car might try and drop down to first gear or something at freeway speed I pulled over, switched the car off, popped the bonnet and had a look around in the engine bay and underneath the car for any thing leaking or looking untoward. The only thing i noticed, and i'm not sure whether this is completely normal or not, but the rear diff casing was too hot to touch, but i had been sitting at 110kph for a couple of hours. I phoned a mechanic mate and he recommended that so long as i hear no grinding clunking sounds or anything out of the ordinary i limp it home,which i did at about 80kph. I also decided not to try the high beams again.

Just around the corner from home, this time going 40 odd kph, i tested the high beams again. This time there was no gear changes, or none that i noticed, but the instrument cluster lit up with every warning light, just like when you start the car, and my passengers noted that the aircon displays and radio switched off for a split second. Once home and stationary i tried the high beam again with no issues.

I'm at a complete loss as to what all that was about, if its a gear box issue or an electrical issue thats causing this problem. Any advice as to how i go about fixing this issue, whether i go to a auto electrician, a auto gear box specialist or just a mechanic would be really appreciated. I need the use of my car, including freeway driving ASAP and at the moment i'm not even keen to take it around the block.

Cheers for the help

Nick

[scotty nm35]

That is very odd Nick, the high beams are controlled by the BCM and the auto by the TCU, the only thing connecting them is the battery and fuse/relay box.

Was it raining at all?

I would start by cleaning the battery terminals and checking the relay box behind the battery for moisture/corrosion. It sounds like there is a short somewhere...

[Commsman]

Further to what Scotty (quite rightly) said, also think about getting your battery tested if it's older than a few years.

I've seen a slightly tired battery cause 'weird' issues that only came good after it was replaced. I've never had a car before where a dud battery caused the most random symptoms. Hope you get it sorted.

[NickM91]

Cheers for the advice,

Checked the battery, negative terminal was perhaps a little loose but otherwise fine, still cleaned them both and put them back on. Relay box seemed fine, no fuses blown or any sign of moisture. Checked around the engine bay for all the earthing points that i could see/find.

As far as battery goes, I had it replaced just prior to my drive across from Perth, about 6000kms, and two weeks ago, so I would have thought it was fine. I've had no other funny things going on up until this point aside from the annoying turbo flutter on medium/light throttle.

So aside from perhaps being caused by a loose negative terminal I'm still at a loss. Is it possible for the gearbox to shift down to say first at freeway speeds? I guess thats my main concern at this point destroying the box and or the engine... confidence in the car is at a new low

[Commsman]

Not likely to be the battery then, but could have been the loose terminal. I know my neg battery terminal is slightly too small for the clamp (even when tight it could be moved by hand). I wrapped copper wire around the terminal & then pressed the clamp over. Now it's tight when done up & has not given me any more trouble.

I doubt the TCU would allow the gearbox to drop into a gear lower than it could handle at any given road speed (the speed wire goes in/out of the TCU so it would 'know').

Just a theory:- the loose battery connection caused your car to think the battery wasn't up to the task when you flicked on high beam, so dropped the gears down to produce higher revs for alternator to boost current.

Could be way off, but let us know if it does/doesn't come back so we can all learn/help more etc.

Edited July 28, 2013 by Commsman

[NickM91]

Commsman, you could be onto something there, my (apprentice)mechanic mate mentioned something along those lines, albeit not knowing the battery terminal was loose, but said he had heard of cars doing it before to compensate for a lack of electrical power for one reason or another.

I need to do a couple of trips to and from Newcastle this week, so that'll be the test I suppose.

[Jetwreck]

Since your going to and from Newcastle and I'm Hornsby why don't you stop be and I'll have a quick look over it for yah!

[NickM91]

Cheers Craig I really appreciate the offer. Like I said I'll be two-ing and fro-ing a bit this week so just let me know when suits. I'm manly way anyway so not that too far any other time.

Chatted to mechanic mate again, said that given the loose terminal, he'd be surprised if it were anything else causing the car to play up.

[NickM91]

almost 1500km since having this issue. no repeat in plenty of night driving selecting high beam etc looking like the loose terminal was the probable cause.

any further thoughts anyone?

[PN-Mad]

almost 1500km since having this issue. no repeat in plenty of night driving selecting high beam etc looking like the loose terminal was the probable cause.

any further thoughts anyone?

Yeah, make sure my battery terminals are nice and tight!

Crazy.....

[Commsman]

Nice result Nick, and cheap to fix

Often it's the simplest things that are the problem - & that's a good thing.

[Daleo]

almost 1500km since having this issue. no repeat in plenty of night driving selecting high beam etc looking like the loose terminal was the probable cause. any further thoughts anyone?

Loose terminals & dying batteries seem to be the source of most random NM35 electrical gremlins.

Mine did all kinds of weird stuff when the battery was dying.