Temp gauge maxed in red right after start up

[cuellar13]

Ok, so I wanna see if anyone has had a similar situation. We are away at our cabin property, and I started the JT up, then the temp gauge was maxed out within a minute or so. I shut it down, popped the hood, and temp seemed normal. Waited a bit, started it up, then the gauge read zero degrees. Drove it about a mile and then I get told Auto stop/start isn't working. Temp gauge still reads zero. CEL comes on, flags the coolant temp sensor. Naturally I would say, ok, coolant temperature sensor needs to be replaced, but that doesn't necessarily explain the Auto stop/start disabling. My JT is a 2020 with 45,XXX miles and the original batteries, so I'm wondering if the secondary battery is wreaking havoc. Gonna pull them both and use a load tester I have here, but of course, this is the holiday weekend and there is no place to get the OE size aux battery, or the coolant temp sensor. Anyone experienced anything similar? If so, was it the coolant temperature sensor? Anyone replace the aux battery with another group size from the local parts store? I really wish I was home, then it could stay down for a few days so that I could order the Genesis set up. Thoughts? Oh yeah, and I'm about a 20 minute drive from "civilization", so that's awesome too.

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[ShadowsPapa]

ok, coolant temperature sensor needs to be replaced, but that doesn't necessarily explain the Auto stop/start disabling.

Yeah, it does.
There's a list of things ESS checks, including operating temp of the cats, and more.
Without knowing the exact engine temperature, the PCM is saying that it can't tell for sure if the engine is up to temperature (a requirement for ESS to work) or over-heated (which leads to ESS not working.
And codes (DTCs) stored will prevent ESS.

So, is the coolant temperature between 40 (104F) and 110 (230F)?

These may be older specs, but it's the idea............

Until that coolant sensor meets with the approval of the computer, ESS will likely not work.

 

[cb4017]

Try bypassing the aux battery. Basically remove the aux battery ground cable then jumper N1 to N2. This will power everything with the main battery.

Good writeup and how-to over on the JL Wrangler forum. I keep a jumper in my kit.

 

[cuellar13]

Yeah, it does.
There's a list of things ESS checks, including operating temp of the cats, and more.
Without knowing the exact engine temperature, the PCM is saying that it can't tell for sure if the engine is up to temperature (a requirement for ESS to work) or over-heated (which leads to ESS not working.
And codes (DTCs) stored will prevent ESS.

So, is the coolant temperature between 40 (104F) and 110 (230F)?

These may be older specs, but it's the idea............

Until that coolant sensor meets with the approval of the computer, ESS will likely not work.

@ShadowsPapa always quick on the draw with tech info! I appreciate it- gonna start there, if anyone has one in stock. Thank you, sir!

 

[ShadowsPapa]

Try bypassing the aux battery. Basically remove the aux battery ground cable then jumper N1 to N2. This will power everything with the main battery.

Good writeup and how-to over on the JL Wrangler forum. I keep a jumper in my kit.

It's not going to work no matter what he does as long as the temp sensor triggered a code and isn't reading correctly.

Battery SoC must also be above 65% so that means, the main battery has to be 12.4 volts or better (typical)
If the main is under 12.4 volts, ESS likely won't work. That's by the book, and pretty much aligns with the testing on mine - unless my main battery wasn't 12.4 volts, ESS didn't work.

But in his case, the reason is obvious - coolant sensor, errors stored, PCM freaked.

 

[cb4017]

It's not going to work no matter what he does as long as the temp sensor triggered a code and isn't reading correctly.

Battery SoC must also be above 65% so that means, the main battery has to be 12.4 volts or better (typical)
If the main is under 12.4 volts, ESS likely won't work. That's by the book, and pretty much aligns with the testing on mine - unless my main battery wasn't 12.4 volts, ESS didn't work.

But in his case, the reason is obvious - coolant sensor, errors stored, PCM freaked.

True. I was initially thinking more along the lines of a dying aux battery causing weirdness and it would be an easy way to troubleshoot it. Main battery would have to be strong though.

A fused jumper is something I keep handy in case I ever have to bypass the aux battery to get home from the middle of Nowhere, NV.

 

[kevman65]

You don't need the OE Aux battery. It's pretty much a standard size motorcycle battery. You can get a better battery that way for less money.

 

[Puch]

Try bypassing the aux battery. Basically remove the aux battery ground cable then jumper N1 to N2. This will power everything with the main battery.

Good writeup and how-to over on the JL Wrangler forum. I keep a jumper in my kit.

I tried finding the answer to this question, but gave up.
Do you know why the jumper can’t be a permanent fix?

 

[cb4017]

I tried finding the answer to this question, but gave up.
Do you know why the jumper can’t be a permanent fix?

Here is the link from the Wrangler Forum:
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/

There are guys over there running it permanent and everything works. I believe they disable or minimize use of the ESS. Also a strong main battery.

 

[cuellar13]

Truck has sat for the last 2 days. I just started it up, CEL is on, temp gauge is now working..... Gonna try to get a coolant temp sensor from the local dealer tomorrow (if they have it) but now I'm wondering about electrical gremlins since it's working again.... or back to potential battery situation. I'm about 3 hours from home, where I would be comfortable taking my time to diagnose, but of course, this would happen during a holiday weekend when we are at our rural property, just outside of a tiny little town. Up to this point, 2/3 of my Dodge/Jeep parts have had issues- I hope this doesn't make it 3/4....

 

[ShadowsPapa]

Truck has sat for the last 2 days. I just started it up, CEL is on, temp gauge is now working..... Gonna try to get a coolant temp sensor from the local dealer tomorrow (if they have it) but now I'm wondering about electrical gremlins since it's working again.... or back to potential battery situation. I'm about 3 hours from home, where I would be comfortable taking my time to diagnose, but of course, this would happen during a holiday weekend when we are at our rural property, just outside of a tiny little town. Up to this point, 2/3 of my Dodge/Jeep parts have had issues- I hope this doesn't make it 3/4....

Don't let the constant talk of ESS and batteries distract.
ESS not working is a symptom, not a cause.
CEL on will likely remain until the error code is reset.

This could be anything from a connection/connector issue to an actual bad sensor.
The thing is that your gauge told you there was a problem - and then people drag the ESS into it when ESS won't work if the ECU detects any other issues, real or perceived.

Did you know you can scroll down and see the ESS status on your cluster?
If you have a battery issue - you'll have other voltage issues and the ESS status screen will normally say not ready, battery charging.

You need logical troubleshooting, not stuff tossed at the wall to see what sticks because people see the ESS term and instantly jump.

ESS and battery issues won't cause your temp gauge issues, but your temp gauge issues will cause ESS issues.

 

[cuellar13]

Don't let the constant talk of ESS and batteries distract.
ESS not working is a symptom, not a cause.
CEL on will likely remain until the error code is reset.

This could be anything from a connection/connector issue to an actual bad sensor.
The thing is that your gauge told you there was a problem - and then people drag the ESS into it when ESS won't work if the ECU detects any other issues, real or perceived.

Did you know you can scroll down and see the ESS status on your cluster?
If you have a battery issue - you'll have other voltage issues and the ESS status screen will normally say not ready, battery charging.

You need logical troubleshooting, not stuff tossed at the wall to see what sticks because people see the ESS term and instantly jump.

ESS and battery issues won't cause your temp gauge issues, but your temp gauge issues will cause ESS issues.

It's not the ESS that I'm super concerned with. ESS is working again, but I got an error for adaptive cruise control when I started it up today. Sorry, forgot to mention that. So, overall, it has gone from normal temp ->"boiling" on gauge->zero temp on gauge->no ESS->CEL->"boiling" on gauge with CEL-> zero on gauge with CEL->normal temp reading with CEL and an adaptive cruise control error. That's what's throwing me for a loop... I'm gonna throw the Coolant Temp sensor at it tomorrow at some point bc I gotta get back home (if I can get my hands on one), so we will see what happens.

 

[Mister Lamb]

At 3 years and 45K miles I'd imagine you're pushing the AUX battery's life anyways. Can't hurt to swap out.. A cheap way to find out if it's the root cause.

 

[cuellar13]

At 3 years and 45K miles I'd imagine you're pushing the AUX battery's life anyways. Can't hurt to swap out.. A cheap way to find out if it's the root cause.

As soon as I'm up and running, I'm ordering the Genesis dual battery set up.

 

[Holes]

Truck has sat for the last 2 days. I just started it up, CEL is on, temp gauge is now working..... Gonna try to get a coolant temp sensor from the local dealer tomorrow (if they have it) but now I'm wondering about electrical gremlins since it's working again.... or back to potential battery situation. I'm about 3 hours from home, where I would be comfortable taking my time to diagnose, but of course, this would happen during a holiday weekend when we are at our rural property, just outside of a tiny little town. Up to this point, 2/3 of my Dodge/Jeep parts have had issues- I hope this doesn't make it 3/4....

ShadowsPapa is not wrong. May not be the answer either. It could very well be as simple as the coolant temp sensor having an internal short.
Hard to say.
If all is good when it’s cold and then it gets wonky when it’s hot maybe it’s a short. ?‍
Follow me for a moment...
So it’s cool and no issues. Then it heats up. Everything reaches operating temperature. Metal begins to expand...

So if the internal wires were haphazardly placed in the sensor on the production line and then they expand and move, and make contact, it could be the issue.

There are literally thousands of what if’s and could it be’s that could cover this.

The “smarter” they make cars, the less able we are to depend on them when there is a tiny insignificant system failure.

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