Hi all,

 

I'm having trouble deciphering the circuit diagrams in the Haynes manual for my 1.4 16V DOHC (AUB) Fabia. Please help!

 

I think I've got a corroded earth point somewhere. the electrics go mental (dials going up and down, lights flashing, all sorts), but when I disconnect the battery for a while the problem goes away for 30 miles or so.

 

Here are the electrics that are going mad:

 

Rev counter (or related sensor)

Oil pressure light (or perhaps switch)

Engine Management light

Coolant temperature dial (or perhaps sensor)

 

(very occasionally and possibly unrelated) Power steering

 

Also problems starting when hot.

 

Is there a common Earth point to all/most of these?? 

 

I have already replaced all the relevant sensors (oil pressure, coolant temperature) and spark plugs. 

 

Please help!!

 

Thanks!

 

Tim

The earth locations are:

• behind battery, on strut tower
• below battery, on side member
• under centre console, in front of gearstick
• at base of LH 'C' pillar

Pulled this from the Haynes manual page 12.21

 

Good luck.

 

SN

I think this is the main earth which goes to the engine.

Thanks Steve for your reply!

 

And thanks Sepulchrave for giving me a specific one to hunt for.

 

The main one that goes to the engine - is that the one connected directly to the battery negative terminal?

 

Thanks!!

 

Tim

Would check the condition of the battery to body negative cable as it is on a tight bend onto the battery it goes brittle overtime! Also is the battery holding charge properly?

Thanks fabdavrav. Yep the battery seems to be fine (have left the lights on by accident a couple of times and had no problems).

ive checked the cable fron the battery with a voltmeter and it seems to conduct fine.

Interestingly I had to drive through a flood the other day (about a foot of water) and the problem went away for 15 mins or so - I guess the water helped the earth connection (although probably made it worse in the long run)

Can anyone tell me which earth point sepulchrave is referring to?

Thanks!

Hi timlovatt

 

Did you ever solve the issue? my car has developed the exact same faults as yours, been tearing my hair out untill i found this thread! someone else has it too! the common theme is earth terminals did that sort it?

On 06/09/2014 at 08:03, timlovatt said:

Thanks fabdavrav. Yep the battery seems to be fine (have left the lights on by accident a couple of times and had no problems).

ive checked the cable fron the battery with a voltmeter and it seems to conduct fine.

Interestingly I had to drive through a flood the other day (about a foot of water) and the problem went away for 15 mins or so - I guess the water helped the earth connection (although probably made it worse in the long run)

Can anyone tell me which earth point sepulchrave is referring to?

Thanks!

Tim- can't help you with the earth point location, but a bit on fault finding. When you have this fault active, use the voltmeter on a volts setting ( an auto ranging with hold would be best)  and look for the volts drop,( between points, e.g. battery negative and the engine etc) possibly when starting the car. Modern voltmeters take that little current that they won't detect a drop with car idle. ( bit too long to explain on a simple post ), so next best way is by detecting the voltage drop between points when a high current is drawn. I don't know the spec for volts drop (=PD) across the joints, but I'd suspect it's very low. e.g. voltage drop across the solenoid ( from an old 70's Haynes for a Maxi) was 0.5v.

Woops -just noticed that the origonal post is six years old, but perhaps this tip might help others

Edited 21 April, 20206 yr by VWD

On ‎06‎/‎09‎/‎2014 at 08:03, timlovatt said:

Can anyone tell me which earth point sepulchrave is referring to?

Answering this belatedly in case it's helpful to Mark. The main chassis to engine earth goes from a stud on the inside vertical face of the left (right as seen from front bumper looking into engine bay) chassis leg, to the top mounting bolt of the starter motor (which is a combined bolt/stud, M8/13mm spanner for the nut on the stud IIRC.  Disconnect battery negative first for safety, then remove and clean both ends of this main earth to engine carefully with fine wire brush or very fine wet and dry (600 grade or so). 

 

And Mark, please let us know if this helps!

 

 

 

 

On 21/04/2020 at 15:12, Wino said:

Answering this belatedly in case it's helpful to Mark. The main chassis to engine earth goes from a stud on the inside vertical face of the left (right as seen from front bumper looking into engine bay) chassis leg, to the top mounting bolt of the starter motor (which is a combined bolt/stud, M8/13mm spanner for the nut on the stud IIRC.  Disconnect battery negative first for safety, then remove and clean both ends of this main earth to engine carefully with fine wire brush or very fine wet and dry (600 grade or so). 

 

And Mark, please let us know if this helps!

 

 

 

 

hi wino, i have one problem with my skoda roomster 5j , warning lights abs. steering flickering voltage when fault active checked volts on cig lighter 4v blank instrument cluster... probably ground connections . found hot main battery earth... but after cranking all reset fine... :(...... can u help to found ground pointbelow battery tray look fine clean not rusty even checked resistance 0.8 ohm .... could not found main engine major ground... where to look ?

imrasl- resistance 0.8 ohms. But from what to what ? IF that is in the main starter circuit, then IMHO it's far too high. At a starting current through that  WILL BE CIRCA 80+ Amps , then volts drop will be 80*0.8 = 3.60 volts( from OHMS law), leaving only 10 volts with a good battery to run electrics . ( As a simple explanation, Ohms law states that when a current flows in a circuit ,then volts will be lost in any bad connection). from my previous posts I advised a voltmeter ( on Volts) be used to test across connectors for volts drops. I gave the example from an old BMC starter circuit of 0.5 v max on the solenoid battery contacts.

thnks for guidance, this 0.8 ohm was from negative battery terminal to the main battery earth. thats was same on all ground points below the battery terminals. today i cleaned a main ground tighted again... but the resistance not checked again... i will update later... as on previous post on the main ground was 0.8 ohm but while in between battery terminal to engine was showing 2ohm ... which is too much high then.... 

 

 

today i measered battery voltage between battery positive and different places on chasis and engine ... all was same 12.45volts... exactly same as on battery itself.

When measuring low resistance values you will need to either "null" the probes, if your meter has such a facility, to remove any error due to the resistance of the leads on the meter or connect the probes together and subtract that value from any readings. Also be sure that the probes are well connected to bright metal otherwise you may get an inaccurate reading.

@VWD isn't 80 x 0.8 actually 64?

 

But yeah, very high resistance, though likely to have been inaccurately measured. 

 

 

it may be error in measuring. will do again and update

Wino- forgive the "senior moment". We all get them. But 0.8 ohms, seems a bit high to me. Perhaps I'd suggest a bit of cleaning/sticking the probe in a bit harder might prodice better results.

26 minutes ago, Liger1956 said:

When measuring low resistance values you will need to either "null" the probes, if your meter has such a facility, to remove any error due to the resistance of the leads on the meter or connect the probes together and subtract that value from any readings. Also be sure that the probes are well connected to bright metal otherwise you may get an inaccurate reading.

Liger- over my years ( 50 +)of testing for resistance on high current problems ,I rely mostly on volts drop over contacts. Modern DVM ( as I've said constantly) have a very low current consumption and will not detect an HR through resistance as the testing current is too low and the voltage too low to show the problems.

On my DVM I ( as on most decent DVM) I have the ability to zero the display , but on cheaper meters, it's simply a maths problem( assuming that "SENIOR MOMENTS' do not occur -Wino- )

Edited 8 July, 20214 yr by VWD

Forget about measuring resistances and concentrate on unbolting/cleaning/refitting the contact points of each end of each earth cable, especially the one between engine and chassis. 

my multimeter show 0.3 0.4  on leads and 0.7 0.8 0.6 ohm measured so total is -0.3.. on continuty it beeps everywhere.. 

 Electrics are not my strong point but, if you have a set of battery jump leads, it may be worth connecting between the battery negative post - not cable - and the engine to rule out any issues with the battery post to inner wing cable and replicate a house wiring ringmain.