Erratic Engine Monitor or battery charging

[paynehowa]

Recently, my 2004 Prius Engine Monitor started acting strangely. The engine monitor bars used to stay between 3 and 5 consistently, moving slowly between these bars.

Within the last month when I start in the morning the bars will usually start at 5 or 6 -- as it was the night before -- but in 3-4 miles as I drive the bars drop from 6 to 2. Sometimes it switches from 6 directly to 4 then directly to 2. Also, now as I drive the bars switch much, much more rapidly then they did before.

Neither the needs maintenance light nor the red triangle have shown up.

I talked with the mechanic at the Toyota Dealer and he said that the Prius monitors itself much more than any other vehicle. If the maintenance lights are not on then there is little that he can do.

Any ideas will help.

[patsparks]

12 volt battery is on its way out, maybe.
How old is the 12 volt battery? Funny things happen when it is on its last legs.

Is the car performing well?

[paynehowa]

Originally Posted by patsparks

12 volt battery is on its way out, maybe.
How old is the 12 volt battery? Funny things happen when it is on its last legs.

Is the car performing well?

Patsparks, thanks for the response. The 12v battery is about 6 months old and the car is performing well. I am just concerned about the big battery or charging system. Thanks again.

[efusco]

While sometimes the 12v can be responsible, and is the least expensive and easiest thing to check, unfortunately those wild swings in the HV battery SOC are often the earliest clues to impending HV battery failure. Have the dealer check it ASAP and don't let them blow you off, esp. if you're still under 100k miles as you should be covered under the hybrid warranty.

[Shawn Clark]

Yep, if you are under 100k you may have just won the hybrid lotto by getting your pack replaced under warranty. While I want my battery pack to last forever, the 2nd best thing would be to have Toyota buy me a new one just before expiration of the original pack's warranty.

[paynehowa]

Evan and Shawn thank you very much. Yes, I have about 75,000 miles. I will get it checked and really appreciate the advise. This was what I was worried about.

[Shawn Clark]

Important tip for you: Make sure that the service ticket/receipt has an adequate description of what you are seeing (erratic energy monitor/battery charging etc.) even if they conclude it is something else. That way in case the HV battery fails at 101,000 miles you have proof that the original problem occurred within the warranty period. I've gotten warranty coverage from Nissan on some engine idle controls that way--had to pay out of pocket and await reimbursement from Nissan.

[Solarman44]

I took our 2004 in for them to check the HV battery because I was concerned about the swing of bars on the MFD. All they did was plug the PC in and "said" all was well. I have come to the conclusion that these "mechanics" just do not know what they are doing.

[statultra]

heres what i suggest, if theres no triangle then theres no problem, continue driving normally. From my experience i can say that if there is a problem with the high voltage battery there will be a sudden swing in the "bars" on the screen, when i mean sudden I mean in a matter of 1 second itll drop to one bar from all green bars.

If the drop is gradual it could just be the 12 volt battery needing charge from startup putting a load on the DC-DC converter, also if you are using the defroster for your front windshield it would turn on the compressor resulting in lower SOC.

I would only get concerned if you see a sudden change in SOC, then again I could be wrong, this was just based on my experience.

When i get a chance ill do some testing on my 01 prius battery which is roughly 9 years old at this point, ill compare it to a gen 2 battery.

[vertex]

Get a volt meter and monitor the 12 volt supply while driving. Should be fairly steady at 13.6 volts or so. If it drops down to 9 or 10 volts, you have either a battery problem, or a charger problem. From your description though, I would focus on the HV pack.