If you have an Android phone, you can buy a ELM327 on Amazon (for under $10, get a Mini version) and buy Torque Pro in Google Play store for Android ($5). For the total of $15 you will have a wealth of various engine information, RPM, current gear, torque converter slip, trans temperature, instant MPG etc..
If no Android phone, just buy an old one off eBay for $10 and keep it in the car.

I run mine on an Android headunit, but works as well on any phone. Transfers to any car, clears CEL codes etc.

 

STANVAN
I have some update for you that I found out .....we talked about the dual batteries and how
using the single switch sometime a person would forget....to change it over ... well I found a unit that
would do that for the individual...self voltage detecting.
Cole Hersee 48530 is the isolator
and the 48513-01 is the low voltage disconnect
I believe I will be using these seems simple.
here are some pics of them and web pages

 

The one on the left is what I've seen before. I helped a buddy troubleshoot a bad one once. I'm not familiar with the low voltage disconnect, but it seems to me that using only the isolator should suffice.

I was going to say what Artie said. I've had one of those Bluetooth OBDII things for a few years(so I paid more ), and I use the free version of Torque. I haven't plugged it up in the Express yet, and am waiting on a friend to root an Amazon Fire to use in the van.

 

I picked up the OEM battery tray today...
i already had an extra retainer and bolt.... ( junk yard )
so once I get the other items in .....
( many still to get ) ... I may do a complete build thread
on just the dual batteries... or maybe I should search this
forum first.. it may have already been done lol

 

Artie1

OK OK Ok.. you now have my head spinning... I had no Idea that what you
have described was even possibly.... lol
So.. looking back at your post to me before it showed that very same pic
that pic.. is the by product of what your talking about...
and that is a result of connecting to the OBDII connector under the dash ?

all with the exception you have to have the APP... from google play store.
and the ELM327
hhhhhhmmmm I like what I am understanding... but its just takin a few
min to sink in.... ( to understand ) .... lol

 

https://www.ebay.com/i/191995262050?chn=ps&dispItem=1

here it is on Ebay pretty cheap .....
looks to be that it has USB also..
but you mentioned bluetooth...
is that how you link the ELM327 to the radio ?
do you have to do this every time you start the van ?

 

HEY... LOOK... Ive got a GMC.... lol
whatcha think now ?

 

So, will you call it a GMC Express, or a Chevy Savannah?

And yes, an ELM327 device is the way to go, but it will not connect to the radio. At least as far as I know. I could be wrong, but I think it will only connect to your phone. But even if it does, only one device will connect to the radio at a time. Bluetooth is like that. That's why I'm going for a separate device. I don't want to give up hands free. I spend too much time in D.C. and Maryland (where hands free is required) to not use it.

 

STAN VAN
You ask all the hard questions... lol

I like. GMC Express... haha. I should say that the next
Time I order a part from the dealer.. lol

Artie1. Says you can blue tooth it to the radio... my stereo
Has bluetooth..and its androide also.... just have to figure out the steps to do it. Im sure there is a utube video lol
I drive hands free but i use my ear buds....

 

Other things to consider; The ELM327 device draws power all the time. And even with a duel battery system, it still draws from battery #1. And the computer doesn't always have "all" the sensors that put out neat info. My 2000 Astro had limited sensors. I was disappointed it didn't do outside temperature, like Da Wife's '05 Equinox. That may have changed by '06. Either way, the device is well worth having.