Possible onboard computer issue

BMW Fanboy · 07-11-2021, 10:48 AM

My Feb 20 430i M Sport is currently on 2338 miles being retired & limited use in lockdown. I haven't reset anything in the onboard computer since picking it up & average MPG is showing 34.8 down from a recent "high" of 34.9. In mid June I did a 480 mile round trip to London from Liverpool & was surprised that the average MPG figure only increased from what was late 32 to 34.9 despite steady motorway driving at speeds between 50 (road works)-70 MPH. Given the constant speeds over several hours I would have expected the average MPG to have gone up more than 2 MPG. Yesterday while on a 40 mile round trip of motorway & 50 MPH roads I cycled through the instrument display using the button on the end of the indicator stalk. That changed the average MPG display to show the current date (correct), current range, average speed & "momentary fuel consumption". I was surprised to see that my average speed was only 20 MPH despite my recent London trip. When in "momentary fuel consumption" the figures constantly changed but didn't make sense jumping from say 23 MPG to 40, 64 to 99 even with the accelerator pedal kept constant. I would have expected the readout to have given a set figure of say 30 MPG going up when I took my foot off the accelerator to going down under firm acceleration. The constant erratic jumping to what appear unbelievable figures to the hardly moved average MPG & low average speed may suggest an issue. Any thoughts people?

robbiep · 07-11-2021, 11:52 AM

The problem is that it takes a lot of a different driving speed or economy to move the longer-term average.

I'd suggest resetting the trip computer on your next fillup (press and hold the button for 3 seconds when showing average mpg, then press and hold for 3 seconds when showing average speed), and then you'll find out what's really happening.

The instantaneous figures for mpg are next to pointless.

Armaan · 07-11-2021, 01:10 PM

If you've never reset it, the average is based on the 2k+ miles, so a trip won't change it much.

Armaan

HighlandPete · 07-11-2021, 03:52 PM

Agree with the other comments. One short trip added to the long range won't make much difference.

I'd be resetting and running both the Trip/Journey and OBC settings, monitor short and long term.

BTW, both should run the same figures, (the figures that run parallel) while on the same reset.

BMW Fanboy · 07-25-2021, 12:57 PM

Thanks everyone for taking the trouble to reply to my post. Yes HighlandPete the totals for the Onboard Computer & Trip Computer in I Drive did read exactly the same for MPG & average speed. Resetting the Trip Computer each time I have used the car it has given different figures to the Onboard Computer the MPG being significantly improved. Off to Suffolk & London mid August so it will be interesting to see what the MPG figure in on a 250+ mile journey.

07-11-2021, 10:48 AM	#1
BMW Fanboy Private 13 Rep 63 Posts Drives: 430iM Sport Join Date: Apr 2021 Location: Liverpool UK iTrader: (0)	Possible onboard computer issue My Feb 20 430i M Sport is currently on 2338 miles being retired & limited use in lockdown. I haven't reset anything in the onboard computer since picking it up & average MPG is showing 34.8 down from a recent "high" of 34.9. In mid June I did a 480 mile round trip to London from Liverpool & was surprised that the average MPG figure only increased from what was late 32 to 34.9 despite steady motorway driving at speeds between 50 (road works)-70 MPH. Given the constant speeds over several hours I would have expected the average MPG to have gone up more than 2 MPG. Yesterday while on a 40 mile round trip of motorway & 50 MPH roads I cycled through the instrument display using the button on the end of the indicator stalk. That changed the average MPG display to show the current date (correct), current range, average speed & "momentary fuel consumption". I was surprised to see that my average speed was only 20 MPH despite my recent London trip. When in "momentary fuel consumption" the figures constantly changed but didn't make sense jumping from say 23 MPG to 40, 64 to 99 even with the accelerator pedal kept constant. I would have expected the readout to have given a set figure of say 30 MPG going up when I took my foot off the accelerator to going down under firm acceleration. The constant erratic jumping to what appear unbelievable figures to the hardly moved average MPG & low average speed may suggest an issue. Any thoughts people? Last edited by BMW Fanboy; 07-11-2021 at 10:56 AM..
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07-11-2021, 11:52 AM	#2
robbiep Brigadier General 1983 Rep 3,216 Posts Drives: VW e-Golf ! Join Date: Dec 2013 Location: North Wales, UK iTrader: (0)	The problem is that it takes a lot of a different driving speed or economy to move the longer-term average. I'd suggest resetting the trip computer on your next fillup (press and hold the button for 3 seconds when showing average mpg, then press and hold for 3 seconds when showing average speed), and then you'll find out what's really happening. The instantaneous figures for mpg are next to pointless.
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07-11-2021, 01:10 PM	#3
Armaan Major 715 Rep 1,158 Posts Drives: F30 320i Sport Remapped Join Date: Feb 2020 Location: Birmingham iTrader: (0)	If you've never reset it, the average is based on the 2k+ miles, so a trip won't change it much. Armaan
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07-11-2021, 03:52 PM	#4
HighlandPete Lieutenant General 6659 Rep 15,858 Posts Drives: BMW F11 535i Touring Join Date: Mar 2007 Location: Scotland, Highland Region iTrader: (0)	Agree with the other comments. One short trip added to the long range won't make much difference. I'd be resetting and running both the Trip/Journey and OBC settings, monitor short and long term. BTW, both should run the same figures, (the figures that run parallel) while on the same reset.
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07-25-2021, 12:57 PM	#5
BMW Fanboy Private 13 Rep 63 Posts Drives: 430iM Sport Join Date: Apr 2021 Location: Liverpool UK iTrader: (0)	Thanks everyone for taking the trouble to reply to my post. Yes HighlandPete the totals for the Onboard Computer & Trip Computer in I Drive did read exactly the same for MPG & average speed. Resetting the Trip Computer each time I have used the car it has given different figures to the Onboard Computer the MPG being significantly improved. Off to Suffolk & London mid August so it will be interesting to see what the MPG figure in on a 250+ mile journey.
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