Consequences of not replacing electric battery heater?

[OrbiterTI4]

Received word today from Tesla Service that my 2015 Model S 85D needs the battery heater (MDL S, DM, THERM SYS, ELEC BATT HEATER 1038901-00-K) replaced (along with some associated small parts, like a bolt). That portion of the service estimate comes out to $890 before tax.

This would be the second the time the battery heater would have been replaced; it was replaced two years ago (Jan 2021) with the same part number/rev (1038901-00-K).

At that time, I received a one-off "vehicle may not restart notice" that prompted my service request, but was told/was of the understanding that the heater was responsible for the pre-heating/optimization of the HV battery for (super)charging.

If that assumption is true (the heater is only useful for supercharging), I would choose to not replace the item as I'm 99% home charging anyway and really don't feel like paying the same $900 over and over. But...I'm seeing other posts getting repeat "Vehicle may not restart" errors along with others, such as "BMS_u008 Acceleration and Top Speed Reduced" and losing regen (Dead battery heater).

Q: Has anyone NOT replaced their knowingly-failed battery heater, and what have been the consequences, if any?

 

[GtiMart]

A cold battery can provide less acceleration power. I've seen a max of 100kW output on my model 3 AWD (+ boost) on a -23C day when I started driving without preconditioning. That is around 125hp, pretty weak. A battery close to freezing will not accept any regen, at least on a model 3. Even on a home charger, the car won't charge the battery until it has reached at least 6C maybe? The model 3 generates heat from the motors so it's different, and target temperatures might be different too, but you would probably have similar issues in relatively similar temperatures. Supercharging requires very high temps that are typically not achieved just by driving.
If you don't supercharge and live in an area where it's always hot, you might be able to get away with it?

 

[vcor]

A battery at or below 32F cannot be charged. What happens when the pack is cold, and you start "charging" it turns on the battery heat until it gets above 32F (or a little higher temp), and even then it will limit charging to be quite slow until the battery gets warmer. So I suspect you'd be fine so long as you don't go down to freezing temps. You can even Supercharge without battery heat at warmer temperatures, but it could charge very slowly. The act of charging can also heat up the pack, but not as fast as with the built-in heater.

The battery heater is also used when driving to heat the battery when you have low temperatures (maybe 50F?) A warm battery has more power than a cold one. So in freezing weather, you can still use the battery, but it has less energy. It seems contradictory but Tesla uses the battery power to run the battery heater and warm the battery. This results in more power than the battery heater consumes.

 

[appleguru]

Really suspect that this part would fail twice in as many years… my money is that something else is causing it to fail, or its a red herring and is fine (but something else is broken).

There was a service bulletin to replace this part for some cars built in 2014, with an “updated revision”… but that new revision was 1038901-00-D. The -K part is several iterations newer and should be fine.

 

[OrbiterTI4]

A battery at or below 32F cannot be charged. What happens when the pack is cold, and you start "charging" it turns on the battery heat until it gets above 32F (or a little higher temp), and even then it will limit charging to be quite slow until the battery gets warmer. So I suspect you'd be fine so long as you don't go down to freezing temps. You can even Supercharge without battery heat at warmer temperatures, but it could charge very slowly. The act of charging can also heat up the pack, but not as fast as with the built-in heater.

The battery heater is also used when driving to heat the battery when you have low temperatures (maybe 50F?) A warm battery has more power than a cold one. So in freezing weather, you can still use the battery, but it has less energy. It seems contradictory but Tesla uses the battery power to run the battery heater and warm the battery. This results in more power than the battery heater consumes.

Appreciate this info. It is rarely below 40°F (maybe one week a year?) and the average overnight low is above 50°F for 3/4 of the year, so from a charging and power available standpoint, I'm probably ok.

I'm curious if there are any other systems that expect to seeing a working heater (and would prompt an alert/error in the absence of one).

 

[Rocky_H]

This would be the second the time the battery heater would have been replaced; it was replaced two years ago (Jan 2021)

Every once in a while, someone gets a really unlucky coincidence in life. You seem to have gotten a short straw on this one--sorry for that.

really don't feel like paying the same $900 over and over.

But now you have convinced yourself that this coincidence is the standard and is going to continue happening to you on this schedule forever. That's not really how that works.

As to whether you can get by with it? Well, it should still function, but noticeably limping. Charging will be the big problem. When it can't heat at all, charging will really be a problem in the Winter. I don't know if it's at exactly 32 degrees, but as @vcor mentioned, when it's about freezing point or below, it simply will not charge until it can warm up, to avoid damaging itself. I have a Zero electric motorcycle that is like that. It will just have to sit somewhere where the air is warm enough, like a garage, for a few hours until it can warm up enough to allow charging.

It should still safely manage that, as it's a progressive scale of how many amps it allows per temperature. Being in Houston, do you get temperatures below 30 F much? Do you have the car inside a garage that can keep it above freezing overnight where it could charge? If it has to sit outside, I think this would be too frustrating to work, but with a decently insulated garage, maybe.

 

[KalJoMoS]

It’s weird that with similar situations some can still use the car. I wish I was able, it’s not pleasant to organise transportation to service as you know how easy it is to drive. Anyhow, as this heater is a part of the HV system then you might end up is this situation. Or you might not, as I have to heat my car every morning almost half a year to get the conditions satisfy for optimal driving.

 

[OrbiterTI4]

Every once in a while, someone gets a really unlucky coincidence in life. You seem to have gotten a short straw on this one--sorry for that.
But now you have convinced yourself that this coincidence is the standard and is going to continue happening to you on this schedule forever. That's not really how that works.

You're right, the failed heater may have just been a bad part. Thinking on it, I've had the battery and regen restrictions almost every morning the past year when it was below 60°F, so now I'm wondering if the heater failed within its 1 yr part warranty, but I hadn't supercharged to get the HV battery system to push an error.

But, after 7.5 years of ownership, the longest my Model S has ever gone without a parts-failed-needs-service event is 15 months. I'm confident something will continue to fail and require service every year. The question is, will it be something that has failed before (door handles, battery heater), or something new...say, the HV battery?

...when it's about freezing point or below, it simply will not charge until it can warm up, to avoid damaging itself...

From a charging perspective, no issue. From a night/morning warm-up perspective to improve performance and maybe resolve the cold morning issues I've seen the past year, probably useful.

It’s weird that with similar situations some can still use the car. I wish I was able, it’s not pleasant to organise transportation to service as you know how easy it is to drive. Anyhow, as this heater is a part of the HV system then you might end up is this situation. Or you might not, as I have to heat my car every morning almost half a year to get the conditions satisfy for optimal driving.

It's funny you mentioned the PTC heater in that post! It was during my warranty days and was due to a condensation drainage issue, but I've had the PTC controller fail in my car and need to be towed and replaced twice.

On the flip side, neither of my battery heater failures have disabled driving beyond giving a "vehicle may not restart" warning. That gets to the crux of the second part of my question; my state requires annual safety inspections, which is due this month(!), and any sort of vehicle alert is an auto-fail. The possibility of the alert popping up again probably pushes this into the "get it repaired again" category.

 

[OrbiterTI4]

I did end up getting the repair.

Costs from the estimate were (using Service Center's $215 hourly rate)...

$430.00 Labor
($107.5 diagnosis, $107.5 Vehicle Electrical Isolation Procedure, $10.75 Isolation/Insulation Test, $204.25 Remove&Replace Electric Heater)
$449.78 Parts
($445 heater, $3 heater module, 2x 0$0.59 bolt, 4x $0.15 hex)

 

[Tezzie]

A battery at or below 32F cannot be charged. What happens when the pack is cold, and you start "charging" it turns on the battery heat until it gets above 32F (or a little higher temp), and even then it will limit charging to be quite slow until the battery gets warmer. So I suspect you'd be fine so long as you don't go down to freezing temps. You can even Supercharge without battery heat at warmer temperatures, but it could charge very slowly. The act of charging can also heat up the pack, but not as fast as with the built-in heater.

The battery heater is also used when driving to heat the battery when you have low temperatures (maybe 50F?) A warm battery has more power than a cold one. So in freezing weather, you can still use the battery, but it has less energy. It seems contradictory but Tesla uses the battery power to run the battery heater and warm the battery. This results in more power than the battery heater consumes.

Where is the PTC heater? Is it near the HV battery? I know a faulty HV battery can catch fire, but can it wreck (overheat?) the PTC heater?

I ask because after I was getting "Car may not restart" alerts, the SC tech first thought it was the HV battering failing, then they decided it was the PTC heater for the battery and replaced it–to the tune of $2407.

2 days after I brought the car home, I got the same "Car may not restart" alerts. I immediately drove it back to the SC. They ended up confirming the HV battery failure, and had the car towed to a bigger SC to replace the HV battery, because they did not have enough space in that facility to safely replace it.

Do you think the HV batter going bad caused the PTC heater to fail? If so, I want to ask them to credit me the $2407 for the PTC heater replacement.

 

[vcor]

I believe the PTC heater is located forward of the battery pack, but even if it caught fire (not that I've ever heard of this), I expect it's far enough away that it would not affect the battery.

I don't see how the HV battery could cause the PTC heater to fail, but I can see a failed PTC might damage the battery (although I think it is unlikely). Software should detect the failed PTC heater and not allow the battery to be used (charged) in a situation that could damage it. I suspect both failed, just close to each other in time. This would be more likely in a high mileage vehicle and/or lots of cold weather driving where the PTC heater is used a lot.