What would cause a racing engine sound from a stop ??

Hi OCD. The revving you heard was due to the state of charge (SOC) of your traction battery being too high (after too much regeneration). This is not really a problem, sometimes it just has to dump some excess battery power so that it has some spare capacity for further regenerative braking. Those of us who live in a hilly terrain are used to having this happen from time to time. Seriously this is nothing to worry about.

There is no problem with your throttle body and your 12V battery is not an immediate issue. It may be a little weak (@12.1 volts) but it definitely didn't cause this problem.

BTW. When the engine is spinning like this to dump excess battery power, surprising as it may seem, the engine is not actually "running". One of the Pruis's electric motors is actually just spinning it (like a giant air pump) purely to dump charge. You can imagine it like someone cranking the starter motor on a conventional car, but without providing any gas or ignition, so basically for no other reason than to try to flatten their battery.

 

BTW. As a general driving tip. If you are regularly seeing "green bars" from just stopping at lights, then you should try backing off the gas a bit earlier and using a little bit of electric propulsion as you slow toward the lights.

In other words, try to balance your gliding and regen a bit more for better fuel economy. Let my try to summarize this as follows.

- Too much EV gliding (overly easy driving) results in less than ideal SOC.
- Too much braking and regen (overly aggressive driving) results in more than ideal SOC.

For best fuel economy try to balance the two.

 

Hi OCD, the tricky thing about testing the 12V battery is that the voltage alone doesn't tell you much about the condition unless you also know what the current draw is at the time. This is why it's really important to test the voltage at least twice. Firstly in "accessory mode" (with as little current draw as possible) and then again in "ignition on" mode (where there is a significant current draw). The really telling thing is the voltage drop that occurs between these two measurements. For example 12.3V for the first one (acc) and 12.1V for the second (ig-on) is not too bad, because although those voltages aren't spectacular, at least it holds the voltage ok under load. If on the other hand someone measured 12.3V for the "acc" measurement and "11.7V" for the "ig-on" measurement then that would indicate the battery is marginal.

So you should repeat those "service menu" measurements that you took on the battery voltage, and make really sure that you take a measurement firstly in "accessory" mode and then again in "ignition on" mode. BTW. To get from "acc" mode to "ig-on" mode you simply press the power button one more time (without your foot on the brake).

You can also take a third measurement in "ready mode" to see the charging voltage, though generally this one doesn't tell you very much about the battery health.

Don't forget to do the test after the car has been sitting (turned off) for at least several hours to make sure the battery is in it's "resting" state. Otherwise you generally get overly optimistic measurements.

 

Try measuring the battery with a volt meter not the MFD. The MFD can under read the voltage by as much as .5volt according to my tests. Meaning the actual voltage of your battery could be 12.6volts.

 

In a small sample of only 5 cars I found that the MFD under read the battery voltage by between .35 and .5volts measured at the same time so giving direct comparisons. The meter I used was calibrated so I know the readings I obtained were correct. On a 12volt battery this discrepancy is substantial in understanding the condition of the battery.

 

Hi Britprius. I agree that the MFD usually measures a little bit lower than the true battery voltage, however I still find that looking at the difference between the "acc" and "ig-on" values to be quite telling. And if someone doesn't have a voltmeter then this info is still much better than nothing.

So far the OP hasn't given us the two values so it's hard to say much about his battery health. We know that he measured 12.1 volts but we don't know if it was "acc" or "ig-on". We need both to really get any clues here.

 

A 3rd option for those who are capable of and comfortable with removing the 12v battery: take it to an auto parts store that has a battery load tester.

 

Hi Uart, While I agree with your post the MFD would be much more use if it is known on any one car the difference in voltage displayed and the real value. My limited research suggests it varies from car to car.

The MFD is better than nothing, but knowing what the MFD would be reading with a known good battery at full charge against readings taken after 4/5/6 years of use would make the decision on whether a battery is good or bad more reliable.

I cannot help but feel in some circumstances perfectly good batteries are being discarded. While I can understand in climates that are extreme, either very hot or cold battery life is shorter, but in moderate climates such as in the UK it is not at all unusual for batteries to last in excess of ten years.

I have changed the battery on my Prius, not because I had a problem with it. I changed it for two reasons.

(1) Because I needed a battery for my sit on mower.
(2) The company I worked for "before I retired" are manufacturing an electric lift mechanism to lift my disability scooter in and out of the rear of my car, so a larger capacity battery (60 amp/hr) made sense. The lift mechanism if successful will be put into production.

 

I guess I must be lucky then, because I get extremely good correlation between the MFD and my DVM measurements in my Prius.

Earlier today I measured the following using both the MFD and a digital voltmeter (DVM) at the front jump point.

Code:

State:    MFD  - Voltmeter
--------------------------
Sleeping: n/a  - 12.39V
Acc:      12.1 - 12.09
Ig-on:    11.9 - 11.89

The above is with fan radio and all other accessories off. Clearly my battery is getting a bit tired and should be replaced soon, however I should mention that I am experiencing no problems and am averaging around 55 MPG (65 MPG UK)

I also searched out an old post of mine from 2009 when I first got the s/h prius. Here I measured the voltages both at the battery terminals directly and also at the MFD. This time I did get very slightly higher readings at the battery, but there was barely anything in it.

Readings from 3 years ago.

Code:

State:    MFD  - Voltmeter
--------------------------
Sleeping: n/a  - 12.58V
Acc:      12.4 - 12.38
Ig-on:    12.1 - 12.21

As you can see I've had excellent voltmeter and MFD agreement with my readings on each occasion, both when using the front jump point and when using the battery terminals directly for the DVM.

BTW. It's interesting to compare these readings from 3 years ago and observe the clear deterioration in my battery's performance. Actually I got the biggest decline in voltage last year after I tried adding distilled water, I think I added a bit too much and flooded the cells, oops. LOL anyway it's still not bad for an OEM battery date coded November 2004!

 

Interesting to note your MFD reading higher than the volt meter, but there is one strange reading from 3 years ago Ig-on: 12.1 - 12.21 where the MFD is under reading by .2 volt. One other point ( not trying to trash your figures) the readings I took were with a newly calibrated bench test meter, unfortunately some DVMs are not as accurate as we would like unless they are the better quality ones such as Fluke and even these vary over time unless calibrated. I agree going to far for the average DIY job.

 

No problems Britprius. I've actually got four different multimeters here, two are quite high quality meters and the other two are "cheapies". With readings around 12V they all agree to within 0.03 volts. Considering that the MFD only measures to one decimal place I am certain that my DVM's accuracy is not an issue here.

Personally I wouldn't make that claim from those readings. Not with the MFD only measuring to the nearest 0.1 volt and those differences being a mere 0.01 volt!

No that's only a 0.1 volt discrepancy. And again considering the MFD resolution, it would (ideally) display 12.1 even if it was 12.149 volts. So that can be explained by as little as about 60mV drop between the battery terminals and the front of the car. There really is nothing that I would describe as an anomaly here. I'm really working within the context of 0.1 volt resolution being good enough here.

 

double post due to network timeout

 

- With the Prius off, and your foot off the brake, press the power button once to get into "accessory" mode.

- With the Prius in accessory mode and foot still off the brake, hit the power button one more time to enter "ig-on" mode.