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Megane Braking Fault.

Mark_L

Well-Known Member
Have a Braking fault on my wife's Megane 2 175dci.

I backed out of a gateway and thd Braking fault came on. Previously had the abs light on.

Bought a genuine sensor from RPD, found the rh front sensor was cut through at the track rod. Also had blown the dash 10A abs fuse.

Tried a different uch,

Abs doesn't work. All feeds and earth's are present at the abs pump, the sensors are all reading through my cheap module. Except 1 reads at 1 per km/H where as the other 3 read at 1 per 10 km/h. Odd. Swapped both front sensors which hasn't changed anything.
It's still reading the same.

Driving me mad and mot next week please help!

@Red21
 
The abs unit is technically vehicle specific and is configured to that vehicle for tyre size,steering angle sensor and suspension type (spring colour code)
Even if the unit was replaced and not configured correctly the road speed reading for each sensor should still display the same data as each other. The tyre sizing is for the correct instrument panel speed display and injection ECU road speed data.

I don't know if it's just my Tool reading it in this way? What I don't understand is driving it with the front wheels in the air, the fault did not re occur. Until all 4 wheels were driven to 10mph.

So I definitely need to look at the connection under the passenger front seat. Can I access it without removing the seat?
 
I have now seen the fault code picture and the title of unknown code is basically saying that the code present is Renault equipment specific and therefore most like only readable via Clip or high end diag equipment.
It is still worth while to check the connectors under seat and as much of the wiring as you possibly can as this could save time (money) or even reveal the cause.
I had a brief look at the Renault fault finding manual for speed sensors and goes like this.

Swap sensors side to side, does fault follow sensor Yes/No
Check for 12 volts at ?? terminal of main loom, present Y/N
Run command to check tooth count, 48 teeth Y/N
Check wiring for short to earth or 12 volts with ignition on wiring disconnected at both ends
Contact technical centre


The Tech centre part, use to mean we need authority or confirmation to replace the ABS module if under warranty or to seek further advice.
Until you can get a recognisable fault code in either Renault DF format or the DTC format we are just plucking ideas from thin air at present.
 
I have now seen the fault code picture and the title of unknown code is basically saying that the code present is Renault equipment specific and therefore most like only readable via Clip or high end diag equipment.
It is still worth while to check the connectors under seat and as much of the wiring as you possibly can as this could save time (money) or even reveal the cause.
I had a brief look at the Renault fault finding manual for speed sensors and goes like this.

Swap sensors side to side, does fault follow sensor Yes/No
Check for 12 volts at ?? terminal of main loom, present Y/N
Run command to check tooth count, 48 teeth Y/N
Check wiring for short to earth or 12 volts with ignition on wiring disconnected at both ends
Contact technical centre


The Tech centre part, use to mean we need authority or confirmation to replace the ABS module if under warranty or to seek further advice.
Until you can get a recognisable fault code in either Renault DF format or the DTC format we are just plucking ideas from thin air at present.

So, just got a call from the mot station and the only fault that comes up is an unstable voltage at the computer.

So it's reading 15v which I'm guessing is too high. With my test it hit 14.8v

All sensors are reading correctly and as they should.

He is saying it could possibly be an earth issue? Another unrelated fault is if you plug something into the cigarette lighter you loose the dab aerial signal which is a new stuck on aerial.

I've checked all the earth's around the battery box and the earth below the abs pump.

What would be useful is if I know where the earth's related to the Abs would be located or a location diagram??
 
I need vehicle details for wiring diagrams, i.e. chassis number

OK, I'll get that. I Have checked the earth which goes to the pump.

Do you think the voltage is too high?

Also when driving the car with the diagnostics reading the fault doesn't come up, even after disconnecting it. No codes are present?

Thanks
 
I need vehicle details for wiring diagrams, i.e. chassis number

So I bought a version of clip and here's a pic of the fault code.

The voltage is running at over 15v and doesn't really change.
Is this correct. Spoke to our alternator repair company and he said some do. But I don't know if this is correct for the megane.

IMG_20200304_202204.webp
 
If you are lucky, click on the repair manual icon and it may load up the relevant PDF file for the checks that are required, If not available I will find the appropriate section.
If the alternator load is high it can run up to 16 volt for short periods, but the norm is 14.5 volts.
On the screen that shows a web type diagram, click on unit 1337 (UPC) then the data page (% icon on the left) this will open a page with a row of tabs & click on the battery tab. This tab should then display some battery & alternator information with one line for alternator load, this should be 99% without the engine running and around 30% with the engine warm & running and no lights, fans or electrical consumers on.
If the battery is in good condition the charge voltage should be around 13-14.5 volts (confirm reading with multimeter on battery)
Turn the lights on & alt load percentage should increase to around 45% and as you turn more consumers on the will increase with an average max of 80%
Increase the engine RPM and the voltage out put & percentage should vary.
If the percentage reading at idle with no consumers on starts off high (high 40's-60%) the alternator demand load or amp output is to high and the reverse if the percentage is to low and erratic voltage control will follow causing spikes & drops that cause havoc with the computers and fault finding.

Going back to the ABS, now that you got Clip do all the road speed readings show the same value when driving?
 
If you are lucky, click on the repair manual icon and it may load up the relevant PDF file for the checks that are required, If not available I will find the appropriate section.
If the alternator load is high it can run up to 16 volt for short periods, but the norm is 14.5 volts.
On the screen that shows a web type diagram, click on unit 1337 (UPC) then the data page (% icon on the left) this will open a page with a row of tabs & click on the battery tab. This tab should then display some battery & alternator information with one line for alternator load, this should be 99% without the engine running and around 30% with the engine warm & running and no lights, fans or electrical consumers on.
If the battery is in good condition the charge voltage should be around 13-14.5 volts (confirm reading with multimeter on battery)
Turn the lights on & alt load percentage should increase to around 45% and as you turn more consumers on the will increase with an average max of 80%
Increase the engine RPM and the voltage out put & percentage should vary.
If the percentage reading at idle with no consumers on starts off high (high 40's-60%) the alternator demand load or amp output is to high and the reverse if the percentage is to low and erratic voltage control will follow causing spikes & drops that cause havoc with the computers and fault finding.

Going back to the ABS, now that you got Clip do all the road speed readings show the same value when driving?

Thanks Rich, I'll try and have a look tonight. I can't drive it as yet with it plugged in as I new a new battery for this laptop. But the values were all correct and as they should be when the mot station checked it for me and he had the abnormal voltage code aswell.

I did check the alternator across the Battery using a multimeter which once settled read 15v but didn't change at all from idle increased revs with everything switched on. No variation which I would expect normally.
 
Alternator control is done by the UPC (1337) via a DSS line.
The upc sends a digital on/off signal to vary the output & load correction.
I'll see if I can find the alternator test as well
 
My 2012 Meg 1.6 dci seems to run at 15v.....it doesn't get used much and I think battery is getting a bit tired, it went flat when I was using Camprust for a couple of weeks, so checked charging with meter and was a bit worried it was that high!......it's stop start model so battery is AGM big cranking amps, I was a tad concerned when I saw how much it was to replace....tight arse.
 
My 2012 Meg 1.6 dci seems to run at 15v.....it doesn't get used much and I think battery is getting a bit tired, it went flat when I was using Camprust for a couple of weeks, so checked charging with meter and was a bit worried it was that high!......it's stop start model so battery is AGM big cranking amps, I was a tad concerned when I saw how much it was to replace....tight arse.

Tell me about it, the alternator is £265+vat! Trade. Need to sell a kidney..
 
Sorry it's going to be Monday now before I can find the appropriate information as we had a massive internet outage yesterday which is still going on, and as all things are now web based today has been painful at work
 
Sorry it's going to be Monday now before I can find the appropriate information as we had a massive internet outage yesterday which is still going on, and as all things are now web based today has been painful at work

Monday will be great. Hope it all gets sorted for you! I'll plug it in again over the weekend and do the checks you mentioned. 👍
 
Last edited by a moderator:
Sorry it's going to be Monday now before I can find the appropriate information as we had a massive internet outage yesterday which is still going on, and as all things are now web based today has been painful at work

So, I tested the voltage % at idle and recorded a video. I'm not sure if you class it as erratic, seems to vary.



Also under load,


Hope these links work..
 
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