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Discussion Starter · #1 ·
There are many posts on this, but I really cannot believe how inaccurate the trip computer is! I own a 156 1.9 16v JTD, and I'm getting over 500 miles to a full tank of diesel. Acceptable or not? I'm not particularly sure, I think I worked the fuel consumption out to be around 41mpg or thereabouts - this is for approximately 75% motorway mileage. But compared to the Subaru I'm getting double the mpg so I'm pretty pleased with that.

My question is, what is this trip computer wired into? If I reset the mileage on the speedo' display, and then on the trip computer, the total distance covered does not even match up! For example, if I do a commute of 35miles, the oddometer in the speedo display will read 35 miles, but the trip computer always reads about 12 miles! Likewise, if I travel 500 miles, the trip computer reads around 190 miles! The average fuel consumption pretty much always reads 23mpg as well.

Did these cars leave the factory with a trip computer so inaccurate, or is this something that gradually loses its calibration over time? Is there anyway to reset it and get it reading correctly?
 

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I've had several 156's. The MPG was always optimistic, particularly so after a re-map. The mileage figure was always accurate though.
 

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Are you sure it's not resetting in between ?
From the manual:

GENERAL TRIP - TRIP B
The TRIP COMPUTER function gives information relating to the operating status of the vehicle on the Infocenter display. This function comprises
the GENERAL TRIP concerning the complete mission of the car and TRIP B concerning the partial car mission. This function (as shown in the
graph below) is contained within the complete mission. Both functions are resettable.
The GENERAL TRIP displays the figures relating to RANGE, TRAVEL DISTANCE, AVERAGE CONSUMPTION, ACTUAL CONSUMPTION, AVERAGE VELOCITY, TRAVELTIME (complete
mission time).
The TRIP B (with automatic reset each time at least 2 hours have passed since stopping the engine), displays information concerning TRAVEL
DISTANCE B, AVERAGE CONSUMPTION B, AVERAGE SPEED B, TRAVEL TIME B (partial mission time).
 

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Assume an “Italian” calculator is being used by your 156!
Mine says I’m doing 70 mph when I’m actually doing 64mph...:banana:
 

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If you have changed the wheel size to another circumference compared to the original ones the accuracy will be gone as the ECU don't get the correct distance.
doesn't explain the original question of (big) difference between the 2 trip indicator odometers though.
My money is still on the fact that the b-trip resets after 2 hours engine off.
 

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There is an issue, not well known, and difficult to explain, but without doubt your car is afflicted. The trip takes a reading from the speedo, but something blows in the speedo which causes this issue. I believe replacing the speedo is the only cure. I personally believe its a voltage spike from jump starting or similar which is the ultimate cause. Anyway, your symptoms are spot on. What your getting is a confusing mixture of kilometers/litres and miles/gallons. If you set your trip to metric via the centre console buttons, so that your consumption on the trip will read litres per 100 km's, You will start to get average consumption readings somewhere in the region of 8-11 litres per 100 kms. Now, here's the clever bit. Take each litre to be 0.62. So if you get a reading of avg consumption of 9 litres per 100km, then 9 x 0.62 = 5.58. That is your true consumption in litre per 100kms. Enter that into this converter https://www.calculateme.com/gas-mileage/liters-per-100-km-to-british-mpg and you get 50.62 mpg. As a bonus, the kms left and travelled, although it says kms on the trip screen, are actually miles, and will tally with the miles recorded on the speedo trip. I have been doing this mental calculation for 3 years now on my own 2.4, and have come across it on 2 1.9 diesels as well. Its actually very accurate with a brim to brim calculation.
Are you confused yet ? Don't worry, you'll adapt and before long it'll be second nature.
On a side note, you should be seeing better than 41 mpg for a 1.9 16v. Anything else going on mechanically ?
 

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Discussion Starter · #9 ·
Thanks for your help guys, apologies I haven't had chance to respond over the past few days. Hugh Myles is correct I believe, I did do a bit more research on it and what has been said in the above post is spot on.

It's a bit frustrating to be honest, one minute I'm getting a range of 700 miles in the tank, which then drops to less than 300! I'll be on the lookout for a speedo' shortly!

Thanks again.
 
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