Member Since: 23 Oct 2016
Location: Penrith
Posts: 143
IID Voltages
I've got a few queries about the voltages shown by the IID. I'm aware that the IID unit doesn't have an onboard voltmeter, it just reads the voltages detected by the car.
As a bit of background, I've fitted a new Denso alternator recently, and I'm confident that's working well. My battery isn't that old but I think it may have been harmed by the old alternator failing - it's struggling to hold a decent charge.
I've been monitoring the voltages with the IID at the moment - the car is starting and running fine but the battery voltage appears low in the morning (less than 12v). Here's a screenshot of some voltages (ignore the injector values)
So on the bottom of that screen we have 'Battery Voltage' and 'Control Module Power Supply Voltage'. Now both those numbers look healthy to me (this is after a 25 mile motorway drive, external temp around 5 degrees).
My confusion is the voltage shown in the top left of the screen (in green). This started at 15.1v at the beginning of the journey and fell to 13.1v towards the end. What does this value refer to? Is it the alternator output?
31st Jan 2017 3:06 pm
DSL Keeper of the wheelie bin
Member Since: 11 May 2006
Location: Off again! :-)
Posts: 72786
If engine is running that's the alternator output. Looks pretty normal in my non techie experience. And very good injector values too!!
31st Jan 2017 3:14 pm
Disco_Mikey
Member Since: 29 May 2007
Location: Dundee, Scotland
Posts: 20731
Occasionally the voltage "sticks" at a value. I have not been able to find a common trigger for it yet...My D3 Build Thread
Member Since: 23 Oct 2016
Location: Penrith
Posts: 143
Thank you for the replies. So I don't need to worry about that voltage too much then.
Now I need to work out if my battery is bad or I have a drain. I've had a look at the excellent drain guide so I'll follow that when I get chance.
Re Injectors: I've just replaced two injectors (no1 and no3) and the car is much better - when warm they're great but injector 5 is over 1300 when the car is cold - that's getting replaced too any day.
So the voltage in green in the top left, should that just display the 'Battery Voltage' but it's got stuck?
31st Jan 2017 5:50 pm
rsp
Member Since: 11 Jan 2006
Location: Goulburn, NSW
Posts: 161
I have had the same problem with my IIDTool. It seems to give a reading that is too low by around .5v. Eg this morning I measured the battery voltage as 12.7 with the multimeter but the IIDToll reported 12.2v. I have been using the IIDTool quite a bit for voltage readings as part of trying to chase down a battery drain, but have gone back to the multimeter to avoid having incorrect information.Disco 3 TDV6 HSE, Auto, White, Rear Diff Lock. ARB BB, Traxide DBS, GME TX3540S, Safari Snorkel, IIDTool-BT, Doran TPMS, Rijidij Spare Wheel Carrier, Two side by side Drifta drawers, cargo barrier and drop down fridge slide, ARB 47l Fridge, Yokohama A/Ts and out of date 17" Cooper STTs.
1st Feb 2017 3:27 am
PatGAPInnov Site Sponsor
Member Since: 02 Dec 2011
Location: Montreal
Posts: 745
The voltage is actually taken from a message being broadcasted by one of the vehicles ECU on the CAN bus. The IIDTool does not do a direct measurement and therefore the voltage display is for indication purposes only. A good multimeter and current clamps are mandatory when tracing a battery drain.http://www.gap-diagnostic.com/
3rd Feb 2017 10:05 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
Yep, clamps are brilliant but for later vehicles the live data from the BMS is very useful, providing a brace of voltage and amperage information.
Click image to enlarge
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