Trip Computer

[Robbeh]

For some reason when I havn't used the car for 24 hours the trip computer resets itself when the engine starts!

I've used the search funcion and people say its a battery problem but a new battery has being fitted a few months ago, also when I just turn the electrics on the trip still remembers, its only once the engine is started it resets

Any ideas?

 

[Ads_172]

Hmm, mine did it very occasionally when the UCH was on the way out... do you have any electrical gremlins affecting the wipers, windows, indicators, radio, etc?

 

[Robbeh]

Nope, everything else seems fine!

Excuse the ignorance but what is the UCH?

 

[Ads_172]

In the absence of a more technical explanation, it's the computery, electronic-controller-thingy that manages all your electrics, such as the examples below.

When they fail they cause all sorts of havoc!

 

[Robbeh]

Still don't know how to solve this though

 

[keithjames84@gmail.c]

Hi did you ever get to the bottom of your problem ? was it the battery ? I am having the same problem , just recently the trip computer resets its self on start up and there is a funny clicking noise coming from the dash as well but it only does it if the car is left for a long period of time , like 24 hours after it has started i can go out for the day park up and when i start its all fine. Thing is the battery was replaced less then a year ago , nd i checked the volts on it this morning after it happened last night and the battery was at 11.9 v before i started the engine and then i tested the alternator and that was giving me 14.5v so that is ok as well . maybe i need to leave the car for longer and see if the battery looses its charge. Is there anything in the car that could be causing it to drain , there is currently no audio equipment like amps etc in there.

 

[keithjames84@gmail.c]

this morning it also did not reset the clock after i started it with the battery at 11.9v

 

[pete_clio]

anytime trip looses its numbers, its mostly down to the battery, mine appears fine and i changed it and it hasnt happened since

 

[davo172]

Battery you had fitted is probly faulty mate .

 

[Robbeh]

But surely the clock and other things would reset?

I've just beared with it for now as its just a little annoyance, sometimes it can go for a week without resetting then other times it's every day!

 

[davo172]

But surely the clock and other things would reset?

I've just beared with it for now as its just a little annoyance, sometimes it can go for a week without resetting then other times it's every day!

No it wont mate only trip computer will reset mine was same, all other functions work perfect ,even your battery volt readings will seem normal.

 

[keithjames84@gmail.c]

But surely the clock and other things would reset?

I've just beared with it for now as its just a little annoyance, sometimes it can go for a week without resetting then other times it's every day!

This what i figured would happen as well , so i went about checking a few more things this afternoon.

I got the multimeter out again to see if there was any thing shorting and between the battery and the earth there is no short, so i checked see what current it was drawing when the car was off and its only 0.35 then 0.15 A so there is not anything drawing a current from it, going to leave it 24h then check the battery volts again.

But oddly enough when i reconnected the battery the clock had zeroed so had ot re set the time but the trip computer had not , so even with out any power the trip computer kept all the information on mpg etc, etc

 

[keithjames84@gmail.c]

Maybe what it is, is the signal from pressing the stick in your dash that re sets the computer is a positive negative positive pulse , that is at a continuous positive level till it is pressed, then if you disconnect the battery there is no problem as there is no signal so the computer does not re-set .

But when you start the engine with a low battery the draw from starting the engine is enough to drop the voltage to a thresh hold that makes the computer think its got a positive negative positive pulse.

i therefor wonder if the battery is ok if the problem can be resolved by simply adding a capacitor in to the circuit to smooth the effect of the voltage drop as it is only happening for a short period of time, while engine is starting.

However from the fact the open circuit voltage of my battery was 11.9 this morning the battery is prob screwed according to the description of open circuit voltage i found below from wikipedia.

The open circuit voltage, is measured when the engine is off and no loads are connected. It can be approximately related to the charge of the battery by:

Open Circuit Voltage (12 V) Approximate charge Relative acid density
12.65 V 100% 1.265 g/cm3
12.45 V 75% 1.225 g/cm3
12.24 V 50% 1.190 g/cm3
12.06 V 25% 1.155 g/cm3
11.89 V 0% 1.120 g/cm3

Open circuit voltage is also affected by temperature, and the specific gravity of the electrolyte at full charge.
The following is common for a six-cell automotive lead-acid battery at room temperature:
Quiescent (open-circuit) voltage at full charge: 12.6 V
Unloading-end: 11.8 V
Charge with 13.2–14.4 V
Gassing voltage: 14.4 V
Continuous-preservation charge with max. 13.2 V
After full charge the terminal voltage will drop quickly to 13.2 V and then slowly to 12.6 V
Wait at least 12 hours after charging to measure open circuit voltage, the resting time allows surface charge to dissipate and enables a more accurate reading.

 

[dwjeviltwin]

Check your earth strap to the chassis, my old cup was doing the same thing. When running, if you wiggle it, and the engine runs funny, then it will be that.

 

[Robbeh]

How would I find it etc?

<----- Car noob

 

[dwjeviltwin]

Connected from the Black negative terminal of the battery, which goes off to somewhere on the Chassis. Mine had two cables coming off it.