Mystery warning light—What does it mean?

A

Akinto

Member
My 2018 Touring PHEV turned itself off immediately after I started it this afternoon. I had my adult son and daughter in the car, as well as my preschool grandson. We needed to drive 45 minutes for urgently necessary medications. The climate control turned itself off. The power system warning light came on. The car drove without any further trouble, but I was too worried about getting stranded in rural Ontario to stop the engine. I sent my son in to pick up a new 12v battery.

We got all the errands done, and I drove over to a neighbour who has a well equipped garage. The battery tester showed 12.7v. Nothing wrong.

The car turned on and off repeatedly, but the power system light remained on.

What should I do? The closest dealership is an hour away in Huntsville and not Clarity certified, AFAIK.
 
Akinto said:
The power system warning light came on. The car drove without any further trouble, but I was too worried about getting stranded in rural Ontario to stop the engine. I sent my son in to pick up a new 12v battery.

We got all the errands done, and I drove over to a neighbour who has a well equipped garage. The battery tester showed 12.7v. Nothing wrong.

The car turned on and off repeatedly, but the power system light remained on.
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The engine doesn’t stay on, nor does it charge the 12V battery via an alternator, and the 12V battery is not used to start the engine. Did you mean to say that you didn’t want to turn off the power system once it was on?

Was the battery replaced? That wasn’t clear in your post.

Was the battery voltage measured while the vehicle was powered up and in Ready mode? 12.7V is a healthy resting voltage. However, based on your description, the car had just been driven and/or may have been in Ready mode. Under those conditions the battery would have either been fresh off a charging voltage from the DC/DC converter or still being charged by the DC/DC converter. A voltage of 13-14V would be expected in that situation.

Measure the voltage again with the car in Ready mode. Voltage should be 13.5V or higher. If not, there may be an issue with the DC/DC converter.
 
Landshark said:
The engine doesn’t stay on, nor does it charge the 12V battery via an alternator, and the 12V battery is not used to start the engine. Did you mean to say that you didn’t want to turn off the power system once it was on?


Yes, I didn’t want to turn anything off one it was on. I have never given a thought to the power system in 5 years, so I can’t respond to the other parts of your paragraph.

Was the battery replaced? That wasn’t clear in your post.

The new battery is in my trunk. My neighbour didn’t think that the old one was bad.

Was the battery voltage measured while the vehicle was powered up and in Ready mode? 12.7V is a healthy resting voltage. However, based on your description, the car had just been driven and/or may have been in Ready mode.

the car had been on the road for 1.5 hours out of 3.5, sitting in park while family members ran errands. I kept it in Park when he tested it. I think he also tested it while it was off. I’m not sure what Ready mode is.


Under those conditions the battery would have either been fresh off a charging voltage from the DC/DC converter or still being charged by the DC/DC converter. A voltage of 13-14V would be expected in that situation.

I had no idea what was the optimal voltage.

Measure the voltage again with the car in Ready mode. Voltage should be 13.5V or higher. If not, there may be an issue with the DC/DC converter.
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So you think it’s the DC/DC converter rather than the battery?

If I’m talking to a Honda shop, what should I tell them?

Should I put in the new battery just because the original will soon be at the end of its life? And because it might help?


Thanks!!
 
Akinto said:
So you think it’s the DC/DC converter rather than the battery?

If I’m talking to a Honda shop, what should I tell them?

Should I put in the new battery just because the original will soon be at the end of its life? And because it might help?


Thanks!!
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Let’s first step back to where I asked you a few questions. It is challenging enough to attempt an internet diagnosis and the challenge becomes greater with a lack of information. Answers to the questions will help us assist you.

We now know that the battery hasn’t been replaced. Measuring the voltage at the 12V battery with the car in Ready mode is a simple way to determine if the DC/DC converter is functioning properly. Once we have that information we can continue the troubleshooting process. Then I can answer your questions.
 
Thanks so much for your patience. I will go next door to ask my neigbour to test the battery in ready mode.

I just looked up ready mode. Got it!

Thanks,

Alison
 
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The neighbour tells me it tested at 12.7 while in gear. He’s not going to do anything more for me, it appears. Understandable: he’s in his late 80s.
 
Akinto said:
The neighbour tells me it tested at 12.7 while in gear. He’s not going to do anything more for me, it appears.
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In gear? The Ready indicator illuminates when the key fob is present, the brake pedal is depressed and the power button is pressed. It’s what we all do prior to driving the car. I trust the only gear that the car was in while your neighbor was under the hood measuring the battery voltage was Park, with the parking brake set.

If that is the case, the 12.7V reading suggests that the DC/DC converter is not functioning properly. It could be the converter, or it could be a failed or damaged component in the circuitry that is preventing a charging voltage from reaching the battery, such as a relay, fuse, wire or loose connection. I do not have access to schematics for the Clarity Power System, and even if I did, I would be hesitant to offer any guidance, given that you do not even own a multimeter.

Now, to address your questions.

I believe the DC/DC converter, and/or associated circuitry are likely culprits for causing the Power System indicator to illuminate. The 3 main reasons I’ve reached that conclusion are, the 12.7V reading, the fact that the car has powered on and off multiple times with the same battery and that you have only reported a Power System indicator on the dash. A failed/failing 12V battery typically manifests by displaying multiple warning indicators.

Tell the Honda dealer what you know. What you should expect is for them to tell you to bring it in for a diagnosis. Ask if they will charge a diagnostic fee and if so, will any or all of that fee be applied to needed repairs. Alternatively, you could take the car to an auto parts store that offers free OBD code reading to see if the code provides any more information than a “Power System”problem. They may also be able to clear the code. If it doesn’t occur again, then it may have been a false alarm or it could be an intermittent problem. That service is readily available in the US, not sure about Canada.

You could put in the new battery, but unless you’ve had the old battery tested, you don’t know that it is near the end of its life. Bear in mind that the battery in the Clarity is not used to start the engine. Replacing it won’t help if the battery isn’t the problem. It’s just throwing money at parts without a diagnosis. However, if the converter has failed or is failing, you will soon have a dead 12V battery. It may be advisable to keep the new battery or a jump pack in the vehicle until the issue has been resolved.
 
Akinto said:
My 2018 Touring PHEV turned itself off immediately after I started it this afternoon. I had my adult son and daughter in the car, as well as my preschool grandson. We needed to drive 45 minutes for urgently necessary medications. The climate control turned itself off. The power system warning light came on. The car drove without any further trouble, but I was too worried about getting stranded in rural Ontario to stop the engine. I sent my son in to pick up a new 12v battery.

We got all the errands done, and I drove over to a neighbour who has a well equipped garage. The battery tester showed 12.7v. Nothing wrong.

The car turned on and off repeatedly, but the power system light remained on.

What should I do? The closest dealership is an hour away in Huntsville and not Clarity certified, AFAIK.
Click to expand...
I finally got it towed to Huntsville. The Daytime Running Light unit was the culprit.
 
As
Landshark said:
Can you provide us with any additional information, such as the diagnosis and a summary of the work that was performed by the dealer?
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soon as the service department gives me the go ahead, I’ll go get the car and ask for a summary of the work. Then I can post it here.
 
Hi Akinto do you have an update/details on the daytime running lights issue? That's a distinct feature of the Canadian Clarity models as I understand.

Oops I just realized it hasn't been at the shop long enough yet, sorry!
 
sabasc said:
Hi Akinto do you have an update/details on the daytime running lights issue? That's a distinct feature of the Canadian Clarity models as I understand.
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While we’re waiting for the lab results, can you elaborate on the distinct feature of the DRL’s on the Canadian models?
 
In Canada, running lights come on with the car. You cannot drive without running lights.

My unit cracked. Water got in and shorted out lots of circuits.

Honda paid for the towing and the car rental, even though the parts and labour were not covered under the warranty.
 
Akinto said:
In Canada, running lights come on with the car. You cannot drive without running lights.

My unit cracked. Water got in and shorted out lots of circuits.

Honda paid for the towing and the car rental, even though the parts and labour were not covered under the warranty.
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The true culprit seems to be water intrusion that occurred from damage that was not repaired. Given that the part is not covered under warranty, the crack must have developed from something other than poor workmanship or a manufacturing defect.

Are any of the “lots of circuits” that were “shorted out” unrelated to the DRL’s? If so, then the issue could have been diagnosed as the fault of another component on a vehicle which does not have the DRL’s on by default. That would also be a misdiagnosis since the component did not fail or cause the failure. Water intrusion created a short when the circuit was energized.
 
I don’t know which shorts occurred.

and yes, I might not have had this trouble if the darks were not always running.
 
Akinto said:
and yes, I might not have had this trouble if the darks were not always running.
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You would have eventually had the problem. It was just brought to your attention at the first opportunity because the DRL’s are on by default. It could have just as easily been a turn signal or headlight that initiated the sequence of events.
 
Akinto said:
In Canada, running lights come on with the car. You cannot drive without running lights.
Click to expand...
I was thinking the DRL's were always on in the US too.
From the manual, it looks like they are always on except when the headlights are on...
Are you saying that in Canada, the DRL's stay on even when the headlights are on?

Excerpt from the manual:

upload_2023-7-10_12-44-30.webp
 
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