Bad smell under the hood when CTEK connected

[Bob nowak]

Hi Guys, been using the CTEK now for 2 years without issues as my Supra is a weekender
This morning I smelt a very bad smell coming from under the hood so I have switched off the CTEK, checked for hot wires etc but didn't find any, the CTEK is about 3 feet from car smell not coming from there,
Any help or suggestions would be appreciated, thanks

Sponsored

 

[exe36m3]

Can you describe the smell?
Rotten egg?
Burned oil?
Sweetish chemical?
Electrical?
Burned plastic?

 

[Bob nowak]

Can you describe the smell?
Rotten egg?
Burned oil?
Sweetish chemical?
Electrical?
Burned plastic?

Hi, many tha ks for your reply, it smelt rather like vinegar, than anything else

 

[tracer bullet]

Now that it's been unplugged for a while, do you still smell anything?

I can't think how the CTEK would do something but obviously if there's a commonality to it being plugged in then it seems like something could be up.

Are you 100% sure it's connected properly? The connections and related wires should be so big and so low in resistance it's nearly impossible to think how one could be overheating.

 

[climhazzard]

Does your Supra have an aux battery in the engine compartment? (Passenger side near firewall, although not sure if that varies for LHD/RHD)

 

[exe36m3]

Ok learned something new, ran this through AI...
Check the battery!

-----

While AGM batteries are "sealed," they are actually VRLA (Valve-Regulated Lead-Acid) batteries, meaning they have a safety pressure-relief valve designed to release gas if internal pressure gets too high. [1, 2, 3]

Why an AGM Battery Smells Like Vinegar

• Off-Gassing from Overcharging: If the battery is old (2020-era batteries are now 4-6 years old) or has a shorted cell, it will resist charging. This converts the charger's energy into heat instead of chemical energy.
• Boiling Electrolyte: The heat causes the sulfuric acid electrolyte trapped in the glass mats to "boil." When it vents through the safety valve, it releases hydrogen sulfide and acidic vapors that smell like vinegar or rotten eggs.
• Thermal Runaway: In extreme cases, the battery can't dissipate the heat, causing the case to swell or even melt. [1, 2, 3, 4]

Specifics for the 2020 Supra
The 2020 Supra (G29 platform) typically has two batteries: a main AGM battery in the trunk and a smaller auxiliary battery often located in the engine bay (passenger side cowl area). [1, 2]

• If the smell is under the hood: It is likely coming from the auxiliary battery being overcharged by the CTEK, or the fumes from the trunk battery are being pulled forward through the ventilation system.
• Venting Issues: Both batteries should have a small vent tube that routes gasses safely outside the car. If this tube is missing, disconnected, or the opposite side plug is missing, the fumes will leak into the car or engine bay. [1, 2, 3, 4]

Immediate Action

1. Stop Charging: Disconnect the CTEK charger immediately to prevent further heating.
2. Ventilate: Open the hood and trunk to let the toxic/flammable fumes clear out.
3. Replace: A 2020 battery that is venting while on a smart charger is almost certainly at the end of its life and should be replaced before it leaks acid onto the car's electronics.

 

[J29DB03]

Unsolicited advice: get rid of that shitty AGM battery and spend a few extra hundred dollars on a lithium battery. AGM batteries are trash.

 

[Bob nowak]

Now that it's been unplugged for a while, do you still smell anything?

I can't think how the CTEK would do something but obviously if there's a commonality to it being plugged in then it seems like something could be up.

Are you 100% sure it's connected properly? The connections and related wires should be so big and so low in resistance it's nearly impossible to think how one could be overheating.

There is no smell after I unplugged bit and I checked the voltage of the battery, whixh is 13.4 volts, started the car and no issues, haven't plugged the CTEK back in, am a bit scared to be honest

 

[Bob nowak]

Ok learned something new, ran this through AI...
Check the battery!

-----

While AGM batteries are "sealed," they are actually VRLA (Valve-Regulated Lead-Acid) batteries, meaning they have a safety pressure-relief valve designed to release gas if internal pressure gets too high. [1, 2, 3]

Why an AGM Battery Smells Like Vinegar

• Off-Gassing from Overcharging: If the battery is old (2020-era batteries are now 4-6 years old) or has a shorted cell, it will resist charging. This converts the charger's energy into heat instead of chemical energy.
• Boiling Electrolyte: The heat causes the sulfuric acid electrolyte trapped in the glass mats to "boil." When it vents through the safety valve, it releases hydrogen sulfide and acidic vapors that smell like vinegar or rotten eggs.
• Thermal Runaway: In extreme cases, the battery can't dissipate the heat, causing the case to swell or even melt. [1, 2, 3, 4]

Specifics for the 2020 Supra
The 2020 Supra (G29 platform) typically has two batteries: a main AGM battery in the trunk and a smaller auxiliary battery often located in the engine bay (passenger side cowl area). [1, 2]

• If the smell is under the hood: It is likely coming from the auxiliary battery being overcharged by the CTEK, or the fumes from the trunk battery are being pulled forward through the ventilation system.
• Venting Issues: Both batteries should have a small vent tube that routes gasses safely outside the car. If this tube is missing, disconnected, or the opposite side plug is missing, the fumes will leak into the car or engine bay. [1, 2, 3, 4]

Immediate Action

1. Stop Charging: Disconnect the CTEK charger immediately to prevent further heating.
2. Ventilate: Open the hood and trunk to let the toxic/flammable fumes clear out.
3. Replace: A 2020 battery that is venting while on a smart charger is almost certainly at the end of its life and should be replaced before it leaks acid onto the car's electronics.

Many thanks for the info, the smell was coming from the engine bay so I will have a look this morning and check the Auxiliary battery, (I honestly didn't know there was on), will take it to the dealer also and get them to check the battery, it is theboriginal battery, car is November 2021 with less approx 2,000 miles , appreciate the help Guys

 

[i3igpete]

No aux battery in the front for my car, I've been in that windshield wiper/battery terminal area multiple times.

From the AI response you pasted , it only shows up in the z4 30i. The other link it provided was a total hallucination from a Dodge Ram cargo van Facebook page. Come on, are we not even reading things before posting them now?

 

[exe36m3]

Learning something new everyday... the 2.0 Supra got the AUX battery. The 3.0s do not.

"On the 2.0L Toyota GR Supra, the auxiliary (second) battery is located on the passenger side, under a black cover/cowl in the engine bay. It is used for the start-stop system and is not found on the 3.0L model. Note that this is different from the main battery, which is located in the trunk."

But given Bob is in Bali, going to assume he might have the 2.0 car?
(Correction, Bali got the 3.0l per Google).

So last idea...
Have the battery "load tested" at a shop. A 2021 model is reaching the 4-5 year mark where AGM batteries often begin to degrade chemically.
You can also test to see if the start-stop function is acting up. If it is, may also indicate the battery might have a bad cell or on the way out.

 

[Bob nowak]

Learning something new everyday... the 2.0 Supra got the AUX battery. The 3.0s do not.

"On the 2.0L Toyota GR Supra, the auxiliary (second) battery is located on the passenger side, under a black cover/cowl in the engine bay. It is used for the start-stop system and is not found on the 3.0L model. Note that this is different from the main battery, which is located in the trunk."

But given Bob is in Bali, going to assume he might have the 2.0 car?
(Correction, Bali got the 3.0l per Google).

So last idea...
Have the battery "load tested" at a shop. A 2021 model is reaching the 4-5 year mark where AGM batteries often begin to degrade chemically.
You can also test to see if the start-stop function is acting up. If it is, may also indicate the battery might have a bad cell or on the way out.

Hi Guys, many thanks for all your replies,
I do indeed have the 3.0 model, it is the only one in Bali and 1 of 28 only in Indonesia, I checked the engine bay and for sure there is NO auxiliary battery, I have also checked the battery in the trunk and no swelling or damage that I can see, I have reconnected the CTEK and left the hood up to see if we get any mell again and I will for sure take the car to the Toyota dealer and get them to check the battery, I did a test of the battery and voltage is 12.4 v but I haven't tested under starting, yet will do that later this morning,
Some one mentioned to change the AGM battery out with a Lithium battery, they are are actual cheap here about half price of an AGM battery, BMW here are quoting about $400 for AGM, I guess that if I change out the battery then the dealer will have to code it for me as I don't have a clue, cheers Bob

 

[SJ-Ray]

You can easily code the new battery with BimmerLink.

 

[razorlab]

People leaning on LLM for normal simple research is mind boggling.

 

[lucky phil]

Unsolicited advice: get rid of that shitty AGM battery and spend a few extra hundred dollars on a lithium battery. AGM batteries are trash.

Really. Big statement.
Phil

Sponsored