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Recently I had MIMA installed on my Honda Insight.

Randall (highwater) noticed ScanGage reads -0.5 volts lower than his voltmeter.

I realize the Insight is a bit odd and add to that mine is year 2000.

Anyone else wonder about the accuracy of their ScanGage voltage?

Does the setting have an affect on the read ? Fast , slow , normal ?
I don't have an added voltmeter to double check this.
I'd like to know, too .

I don't think the ScanGage refresh rate (fast, slow, normal) is going to be a factor.

I'm nitpicking on SG, but I think it's important to know.

At least on the Insight, voltage drops by about a volt when the car is in AutoStop mode.

Everybody should notice a voltage drop when headlights are turned on - mine drops -0.2 volts.

so its a consistant low voltage read , which is where I was leading with the refresh rate. With the low voltage it seems as if there is calibration error or built in resistance? It's not really nitpicking - especially when it is needed info .
Headlights on the Focus drops -.2v, turn the hi-fi on it will drop another -.2v, give it a few seconds and it jumps right back up to 13.9-14.0v .

Mine reads low compred to 2 volt meters I've used (including the "real-time" one built into my radar detector).

But, is the SG "measuring" voltage, or merely "reporting" voltage that is given to it by the car's computer.?

ScanGage is reading whatever data is coming off the OBDII plug, I'm pretty sure.

While ECUs can report various supply-voltage figures, I
would hope the SG senses it directly from its own supply and
NOT through any incoming diode drops. There's no reason to
introduce that kind of inaccuracy. And if a distinction can
be made between "directly read supply voltage" vs. "the engine
ECM reports ...", that's even better since it allows diagnosis
of possible power issues around the car.
.
_H*

While ECUs can report various supply-voltage figures, I
would hope the SG senses it directly from its own supply and
NOT through any incoming diode drops. There's no reason to
introduce that kind of inaccuracy. And if a distinction can
be made between "directly read supply voltage" vs. "the engine
ECM reports ...", that's even better since it allows diagnosis
of possible power issues around the car.
.
_H*

I would have the opposite philosophy. I specifically want the SG to tell me what the ECU values are so another insturment (e.g. voltmeter) can directly generate a comparison value that will tell me if I need to replace a sensor. For voltage measurements would it be possible for SG to do this comparison itself and report anomalies?

You're actually agreeing with what I said. Allow the SG
to read directly *and* compare ECU figures and look for
discrepancies.
.
_H*

Why would voltage drop when in autostop? I would expect it to drop if the DC/DC turns off, but it doesn't always turn of in autostop; I sometimes see current leaving the battery on the MIMA display when in autostop. 12v voltage isn't something I normally watch on the SG- guess I'll have to try it.

Fenrir, mine drops because the operating voltage is 14V but the battery is only 12V. When the alternator isn't running it drops back to the normal 12V but I see 14V while the engine is on.

Yes, an alternator puts out a nominal 14V, but the Insight has no alternator. Instead, it has a DC to DC converter which takes the high voltage from the hybrid battery pack and drops it to 14.5V to charge the 12V battery. The DC/DC converter only runs when the 12V drops below a certain voltage.

It could be there's a difference in behavior between 2000 Insights and newer ones (mine is an '03). Perhaps the DC/DC converter in a 2000 is always off when in autostop. I've read reports of 'recals' resulting from long periods in autostop. This is believed to be caused by the 12V voltage dropping to a point where it no longer provides sufficient power for the computers (BCM in particular). A weak 12V battery would be masked by the DC/DC staying on longer.

I'm pretty sure the ScanGauge reads voltage directly from the OBDII power source, and isn't parroting a reading from the ECU. I get voltage readings that are consistent with my use of accessories even when the engine and ECU are all shut down. Even during my Subaru's interminable 15-second bus reset period (during which my SG can't communicate with the ECU) it reports the voltage in a consistent manner.

As for the actual accuracy of the voltage reading, I guess I'll have to dig out the multimeter and check it. I get indicated 13.7V or so when the engine is running and mid-12s immediately after shutdown. Starting difficulties ensue when indicated voltage drops below about 11.6V.

Here's what mine looks like.
DVM plugged into the power socket on the dash.

http://www.cleanmpg.com/photos/data/500/IMGP2215.JPG
Reading taken with key on, no ICE start.

http://www.cleanmpg.com/photos/data/500/IMGP2217.JPG
Reading with the DC/dc engaged with the FAS switch. Still no ICE.


Randall

I can confirm that my 12V voltage does not drop when in autostop. It goes up during regen as I slow to a stop, because the DC/DC takes the opportunity to recharge the 12V. In autostop, the DC/DC will still come on if needed. For instance, if, in autostop, I turn on the headlights, 12V drops, then the DC/DC kicks on and voltage on the SG goes up to about 13.7V.

So I'm wondering if the voltage drop Chuck is seeing is because regen has stopped, and not simply because the car is in autostop.

I've driven Chuck's Insight after the MIMA install several times, and his acts the same as mine. Mine is early '01, his '00.

Randall