Any Auto Technicians Here?

[Milf Dots]

Any Auto Techs here? My buddy's 17 year old kid just cross cabled a jump start attempt. He quick pulled the cables, put them on right, got the car started, but the car will only idle and drive at about 3 mph- I read about something called Limp Mode?

Anyway, he said the battery tested good, he can run the A/C, but the engine ignores the throttle position because he thinks the computer has locked out the throttle as a precaution?

TYIA

 

[hlee]

Yeah, “limp mode” is a thing. Your buddy should research it for the specific car model.

 

[jetracer013]

Check engine light? Everyone should own a scanner. They’re like 30 bucks now.

I’d bet he flew fuses.

 

[Numedal]

If he crossed jumper cables, a good place to start would be fuses. Had vehicles in where that was done which blew a bunch of fuses, made all kinds of weird issues.

 

[The D]

Fucking yikes. There are probably a few fuses blown and maybe even a control unit. Check all fuses, there may be some pretty big ones in a hidden fuse box somewhere, and as many vehicle operations as possible. If a blown fuse or three doesn’t get it fixed it will need to go to someone who knows what they’re doing

 

[34vld]

Discconect both battery cables and hold them together for 30 seconds then hook them back up, check for bad fuses and see if it works

 

[Bacarrat]

Any Auto Techs here? My buddy's 17 year old kid just cross cabled a jump start attempt. He quick pulled the cables, put them on right, got the car started, but the car will only idle and drive at about 3 mph- I read about something called Limp Mode?

Anyway, he said the battery tested good, he can run the A/C, but the engine ignores the throttle position because he thinks the computer has locked out the throttle as a precaution?

TYIA

What year make and model vehicle would help. Surprised it even started. Most of the time you will blow the Mega fuse. At worst he might have taken out a a control module. I have had plenty of car salesman tried to jump start a new car with dead batteries before. On Chevys you will blow the mega fuse. Easy fix for the most part. Other manufacturers might wire up their vehicles differently.

 

[Kiba]

Hopefully all that happened is a couple of popped fuses, that's typically what happens.

The momentary reverse polarity can also damage the battery. Not as cheap as popped fuses, but better that BBQ'd modules.

Worst case is one or more damaged modules from the reverse polarity.

I've seen all three situations happen from reverse connected jumper cables.

Even in the event no fuses popped or nothing is permanently damaged sometimes a hard fault code and limp mode can be tripped which will likely require a scanner to clear.

Also, if the car needed a jump, was it because they left the lights or something else on and ran the battery down, or is the battery weak and needing replacement? A battery in poor condition can cause all kinds of weird symptoms across multiple systems in a modern car, so don't rule out a bad battery... I've seen thousands of dollars of parts thrown at a car to correct multiple ECM, TCM, and BCM related faults and the root cause was a bad battery, lol

 

[Maggot]

Hopefully all that happened is a couple of popped fuses, that's typically what happens.

The momentary reverse polarity can also damage the battery. Not as cheap as popped fuses, but better that BBQ'd modules.

Worst case is one or more damaged modules from the reverse polarity.

I've seen all three situations happen from reverse connected jumper cables.

Even in the event no fuses popped or nothing is permanently damaged sometimes a hard fault code and limp mode can be tripped which will likely require a scanner to clear.

Also, if the car needed a jump, was it because they left the lights or something else on and ran the battery down, or is the battery weak and needing replacement? A battery in poor condition can cause all kinds of weird symptoms across multiple systems in a modern car, so don't rule out a bad battery... I've seen thousands of dollars of parts thrown at a car to correct multiple ECM, TCM, and BCM related faults and the root cause was a bad battery, lol

This. My 2022 Corolla started acting really funny, all kinds of little dash lights, and slmething I dont rememeber. Took it to the deaer sweating my wallet. Big relief, needed a battery.

 

[Bantam1]

More than likely a fuse or even possibly a relay could have been damaged. It depends on the vehicle as all do things a little differently. I am surprised it started usually they pop one of the main 80-100 amp fuses or melt a fusible link (old cars). It could have even melted a smaller ground wire somewhere if the fuse didn't pop. Hopefully he learned from this mistake.

 

[atomic41]

Also, if the car needed a jump, was it because they left the lights or something else on and ran the battery down, or is the battery weak and needing replacement? A battery in poor condition can cause all kinds of weird symptoms across multiple systems in a modern car, so don't rule out a bad battery... I've seen thousands of dollars of parts thrown at a car to correct multiple ECM, TCM, and BCM related faults and the root cause was a bad battery, lol

This. A low battery on modern cars causes all kinds of issues.

 

[The D]

This. A low battery on modern cars causes all kinds of issues.

This.

I’ve had to tell plenty of people that their new $75 Auto Zone battery is dead a month after I told them their $150k Mercedes needed a battery

 

[Maggot]

More than likely a fuse or even possibly a relay could have been damaged. It depends on the vehicle as all do things a little differently. I am surprised it started usually they pop one of the main 80-100 amp fuses or melt a fusible link (old cars). It could have even melted a smaller ground wire somewhere if the fuse didn't pop. Hopefully he learned from this mistake.

First thing that came to my mind was that meme with the guy saying "They want to change the world but they cant even change a tire." Just sub jump a battery, LOL.

But fuck, we all make mistakes...except me.

 

[Maggot]

This.

I’ve had to tell plenty of people that their new $75 Auto Zone battery is dead a month after I told them their $150k Mercedes needed a battery

Which battery would you recommend? I looked around and the best deal I've found is Sam's Club. They have a 3 year with a really good warranty for about $100-120 depending on vehicle. The one in my 2002 Chevy Express lasted 3.5 years.

 

[Bacarrat]

There are only like 2 or 3 car battery manufacturers in the US. It's a straight gamble on how long they last. More expensive doesn't always mean better. I have seen new vehicles with less then 10 miles with dead batteries, and I have seen vehicles with over 100k and over 7 years old with original batteries. So many variables on how long they last. My last car, it use to go through batteries once every 2 years, but the last one lasted 6 years until I got rid of the car.

 

[The D]

Which battery would you recommend? I looked around and the best deal I've found is Sam's Club. They have a 3 year with a really good warranty for about $100-120 depending on vehicle. The one in my 2002 Chevy Express lasted 3.5 years.

Whatever direct fit replacement you can find. Just like engine oil, everyone has their preferred brand but they’re all ok. If your vehicle was originally equipped with an AGM battery, get an AGM replacement. You can get an AGM for a non-AGM equipped vehicle(I do) but don’t go the other way. That was the biggest problem with Mercs, people tried cheating out with a non-AGM battery in something that had 50 control units and a million feet of wiring

 

[Redmanss]

Whatever direct fit replacement you can find. Just like engine oil, everyone has their preferred brand but they’re all ok. If your vehicle was originally equipped with an AGM battery, get an AGM replacement. You can get an AGM for a non-AGM equipped vehicle(I do) but don’t go the other way. That was the biggest problem with Mercs, people tried cheating out with a non-AGM battery in something that had 50 control units and a million feet of wiring

Retrofitting to an AGM from stock lead acid needs a bump in charging amperage. They work without it, but it degrades the life span and benefit of paying 50% more for a battery. Easy change with a mid grade code reader (brand dependent), or slipping the tech a Jackson at the dealership for an oil change.

Heat kills batteries the most, followed closely by shit alternators, but oxidation on the connections causes a lot of otherwise good batteries to be replaced before their time is up. A $5 battery terminal cleaning brush and some no-ox or similar oxidation inhibitor should always be step one to troubleshooting a bad battery.

And like in Ghostbusters, don’t cross the streams. It lets the magic smoke out that makes computers do stuff and shit. Hopefully a fuse protected the FM (fucking magic) from escaping.

 

[P-Squared]

Oh how I miss 6v systems with generators. OK I'll even include 12v systems, but they have to have the generator and mechanical voltage regulators.

OK, I'll say it for you... shut up boomer.



P.S. and tube radios.

 

[zeroz]

Again, what kind of car could help us help you. Could be as easy as cycling the car on and off a few times to reset the computer/check engine light or could be blown fuses and modules.

 

[GreenGO Juan]

rut row shaggy...

 

[Thump_rrr]

Which battery would you recommend? I looked around and the best deal I've found is Sam's Club. They have a 3 year with a really good warranty for about $100-120 depending on vehicle. The one in my 2002 Chevy Express lasted 3.5 years.

I don't look for the best deal.
I look for the best battery for the application.
I like Varta batteries which are an OEM for Mercedes.

 

[sirhrmechanic]

Just hope it’s not a newer car and that the central computer didn’t get zorched!

There are supposed to be safeguards.

BUT… strange things can happen that put a jolt into the ECU’s and similar systems.

It can be like when the monkey peed into the cash register… it will run into money!

Sirhr

 

[LuckyLuke80]

That’s why I drive old cheap cars. No sensitive wiring to fry. Just a cool spark shower if you accidentally grab the terminals backwards

 

[JoshPutman]

Remember kids, if it's got tits or tires, you're gonna have fucking problems.

 

[Milf Dots]

Again, what kind of car could help us help you. Could be as easy as cycling the car on and off a few times to reset the computer/check engine light or could be blown fuses and modules.

It's a 2010 Toyota Camry.

 

[supercorndogs]

That’s why I drive old cheap cars. No sensitive wiring to fry. Just a cool spark shower if you accidentally grab the terminals backwards

I replaced a bunch a fuseable links on about a 1985 Ford f150 that a kid reversed the jumper cables on....

 

[TahoeDust]

Every car should have "jump box" in the trunk. They are cheap and any decent one will protect from cross polarity.

 

[Bantam1]

It's a 2010 Toyota Camry.

He got lucky if this did not pop the main fuses/fuses. I used to be a Toyota tech for a long time. Toyota likes to keep the hot side hot and turn on grounds to power a circuit.

A lot of the newer cars the battery is part of the circuit and they will not run if the cables are disconnected with the car running. Clearly the car had a battery issue and more than likely needs a replacement. Like others have said new batteries are a gamble. Most are refurbs essentially (the reason you have to give them a core). Interstate used to be good batteries or at least they were when I was still a tech. I have no idea now. I would just get whatever the local auto parts store has a have him get one of the jumper boxes to carry just in case for future needs.

Start there and see if that helps him. The PCM and other parts that require protection should escape damage from a reverse power like he did. Powering off the vehicle during the battery swap should also reset the PCM if you do not have a scan tool. The KAM will have no power so it should go back to factory default. I would also follow the battery cables to where they lead and check for any damage like melted insulation or signs that could lead to a short. He may have got the cables off in time before anything melted and popped the fuses.

 

[E. Bryant]

Just hope it’s not a newer car and that the central computer didn’t get zorched!

There are supposed to be safeguards.

BUT… strange things can happen that put a jolt into the ECU’s and similar systems.

It can be like when the monkey peed into the cash register… it will run into money!

Sirhr

1) There is no "central computer" on a modern car; in fact, quite the opposite (it's a distributed network).

2) Many of those modules are indeed pretty frickin important. Because of this, virtually every electronic module is protected against reverse voltage (-14VDC for 60 sec per ISO 16750-2 4.7) and either will not draw current (diodes are a remarkable invention) or will pop fuses as protection.

Alternators are notable exceptions - maybe the fusible link pops, or maybe one or more rectifier diodes blow (we joke that this is desirable in order to protect the fuse).

 

[GreenGO Juan]

It's a 2010 Toyota Camry.

Trying to Dia something like this, over the internet, through you, to a 17 year old is not ideal.

The suggestions made, ie hook up a scan tool, read clear codes, reset out of limp mode, look for obvious damage is about as good as it will get. Luckily it will be that simple.

If that doesn't work find a local tech, as its a crap shoot to guess what it might have fried.

 

[sirhrmechanic]

1) There is no "central computer" on a modern car; in fact, quite the opposite (it's a distributed network).

2) Many of those modules are indeed pretty frickin important. Because of this, virtually every electronic module is protected against reverse voltage (-14VDC for 60 sec per ISO 16750-2 4.7) and either will not draw current (diodes are a remarkable invention) or will pop fuses as protection.

Alternators are notable exceptions - maybe the fusible link pops, or maybe one or more rectifier diodes blow (we joke that this is desirable in order to protect the fuse).

Since he didn’t tell us what it is or year… I didn’t assume Canbus…. But I get your point.

That said, I had a wonderful 1998 MB 300SL. The last of the straight six wedge drop tops. It does over the winter and so I sent to the dealer to start it. They must have jumped it wrong because their explanation was “all 5 computers failed simultaneously and sorry, it is 2 weeks out of MB Certified used warranty. That will be $5k please.

The Conti-R Bentley I had and sold last year… if you jump started it with the drivers dooor open, it would fry the main computer. New ones in 1998 were $30,000. Fortunately there is now a guy in NJ who uses a Subaru computer, wipes it and puts in new code. So if you zorch your Turbo Bentley it’s only a cheap $5k or so now!

But, yeah, probably todays cars are better protected.

That said, I never even attached a trickle charger without taking the battery posts off! And cut off the main switch before reconnecting. Paranoia runs deep!!!

 

[E. Bryant]

Since he didn’t tell us what it is or year… I didn’t assume Canbus…. But I get your point.

That said, I had a wonderful 1998 MB 300SL. The last of the straight six wedge drop tops. It does over the winter and so I sent to the dealer to start it. They must have jumped it wrong because their explanation was “all 5 computers failed simultaneously and sorry, it is 2 weeks out of MB Certified used warranty. That will be $5k please.

The Conti-R Bentley I had and sold last year… if you jump started it with the drivers dooor open, it would fry the main computer. New ones in 1998 were $30,000. Fortunately there is now a guy in NJ who uses a Subaru computer, wipes it and puts in new code. So if you zorch your Turbo Bentley it’s only a cheap $5k or so now!

But, yeah, probably todays cars are better protected.

That said, I never even attached a trickle charger without taking the battery posts off! And cut off the main switch before reconnecting. Paranoia runs deep!!!

The Germans in particular are known for being better at complexity than reliability, but their customers are quite happy with the dealership experience so there's not been much incentive to change.

The less said about British automotive electronics, the better.

Assuming that a manufacturer has designed its electronics to pass ISO 16750 or its many derivatives (such as GMW 3172), you're generally going to have a reasonable level of robustness. At that point, the reliability of the wiring harness and connectors is the largest source of problems, and unfortunately some things have gone backwards in this area in the pursuit of recyclability and cost savings.

 

[ggmanning]

Check the fusible link and verify it's good the alternator is charging the battery to spec.

 

[Bantam1]

I always found the German cars had electrical issues and great mechanical build quality with some exceptions to recent model cars where the durability is not as good as it used to be. One of my friends is a long time BMW tech. He told me with the new stuff if you get one lease it or dump it before they hit 100k miles. I guess the cam advance mechanism likes to fail on the newer inline 6 engines around 100K+ and it costs a lot to replace it and you need a special computer/scan tool to recalibrate it.