C4 will only start with abs disconnected

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Currycowboy
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C4 will only start with abs disconnected

Post by Currycowboy »

Hi, really hoping no I can get some help. Bought this vehicle as a non starter. It has had a number of “mechanics” look at it here where I live in spain. They changed the fuse/relay Board (BSi) a few times prior to my purchase but only seemed to make the issue worse. I know an English Mechanic who seems to know his onions and pinpointed part of the issue to the ABS Pump/module. When this is disconnected the car will start and engine will run. He said he believes the pump is the issue. Can anyone confirm this to be the case from experience or should I be looking for a wiring fault somewhere? Any schematics/wiring diagrams greatly appreciated if that’s the case.
wheeler
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Re: C4 will only start with abs disconnected

Post by wheeler »

Can you confirm that when the ABS module is disconnected are the CAN lines being bridged out also or the unit just simply unplugged?
If it is just unplugged I would expect that the car wouldn't start as this breaks the CAN connection between the BSI & engine ECU.
Currycowboy
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Re: C4 will only start with abs disconnected

Post by Currycowboy »

I am fairly certain just unplugged and car starts but just messaged the mechanic to double check
Currycowboy
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Re: C4 will only start with abs disconnected

Post by Currycowboy »

Ok Wheeler, I have had confirmation, it was simply unplugged nothing being bridged and the car starts and engine runs. With the abs connected the car will not start.
Nemo26
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Re: C4 will only start with abs disconnected

Post by Nemo26 »

Check for 5V referent voltage with pluged and unpluged abs. You have 100% absence of 5V referent voltage with abs connected. Next step: see wiring diagram, and disconect abs sensors one by one to find shorted sensor. If sensors are not shorted check wiring to/from sensors. If everything is ok you can condemn abs/esp module.
Currycowboy
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Re: C4 will only start with abs disconnected

Post by Currycowboy »

Nemo26 wrote:
02 Jan 2019, 22:50
Check for 5V referent voltage with pluged and unpluged abs. You have 100% absence of 5V referent voltage with abs connected. Next step: see wiring diagram, and disconect abs sensors one by one to find shorted sensor. If sensors are not shorted check wiring to/from sensors. If everything is ok you can condemn abs/esp module.

Thanks for your reply Nemo26. I Don’t have any wiring diagrams, are they posted in here? Do you have a link please? Where would I be checking for voltage and please explain “referent” voltage. Please excuse my ignorance I am happy to be educated.
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GiveMeABreak
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Re: C4 will only start with abs disconnected

Post by GiveMeABreak »

Currycowboy wrote:
01 Jan 2019, 15:04
Hi, really hoping no I can get some help. Bought this vehicle as a non starter. It has had a number of “mechanics” look at it here where I live in spain. They changed the fuse/relay Board (BSi) a few times prior to my purchase but only seemed to make the issue worse. I know an English Mechanic who seems to know his onions and pinpointed part of the issue to the ABS Pump/module. When this is disconnected the car will start and engine will run. He said he believes the pump is the issue. Can anyone confirm this to be the case from experience or should I be looking for a wiring fault somewhere? Any schematics/wiring diagrams greatly appreciated if that’s the case.
Pop up your VIN here and I'll see about a wiring diagram.

I doubt it will be the ABS sensors themselves as this would normally give you an ABS warning light on the dash AND a relevant fault code that should identify the relevant wheel sensor if that was the case. Have you had it properly diagnosed with Lexia yet?

The other thing you need to check is the car battery itself. As the ABS system engages the moment the ignition is turned on, if the battery is very weak then it could be enough to prevent the car starting. Don't discount a weakened battery - and even more so as you have been probably weakening it further from the attempted starting.

If the battery is weak, the ABS ECU may not record a permanent fault if the voltage does not meat the 7.7 Voltage threshold to trigger a P0562 fault, but could be enough to light the ABS warning light until the engine is started and the voltage increases.

So a couple of things - ensure the battery is in good condition and charged and get the car on a Lexia (with the ABS module attached) and run a full diagnosis. Report any fault codes back here and we can maybe help further.
Nemo26
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Re: C4 will only start with abs disconnected

Post by Nemo26 »

5V referent voltage is kind of ecu's nerve system. It's shared trough various sensors, and ecu determines position of measured conponents in reference to that voltage. If there is no referent voltage (short sensors that shares that voltage or wiring) ecu is not in controlle, and than you have no start/no comunication condition. Voltage is tipically measured on tpms sensor with sensor connected, but can be measured from any other aensor that shares it.
Currycowboy
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Re: C4 will only start with abs disconnected

Post by Currycowboy »

Nemo26 wrote:
03 Jan 2019, 12:12
5V referent voltage is kind of ecu's nerve system. It's shared trough various sensors, and ecu determines position of measured conponents in reference to that voltage. If there is no referent voltage (short sensors that shares that voltage or wiring) ecu is not in controlle, and than you have no start/no comunication condition. Voltage is tipically measured on tpms sensor with sensor connected, but can be measured from any other aensor that shares it.


Thanks. Here is my VIN VF7**************[VIN obfuscated, can be read by forum staff]
Brand new battery purchased. So highly unlikely to be battery Voltage. Fault was there prior to purchase and what previous techs had been trying to solve. Was aware battery condition is paramount on many Citroen’s, so bit the bullet on that one straight away. Not sure anyone will have Lexia here so was thinking about buying disc and cables on ebay and hooking it up on my pc or buying a dedicated toughbook for running diagnostic software on as I often buy and sell cars and it’s pribably about time I invest some money on it. So won’t have anything for a while other than Launch diagnostic codes, as that is what my mechanic has.
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GiveMeABreak
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Re: C4 will only start with abs disconnected

Post by GiveMeABreak »

Yes, get a dedicated laptop for the job as Diagbox is a really messy installation. At least it will do all Citroen, Peugeot and DS Automobiles vehicles, so an investment if this is what you do.
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GiveMeABreak
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Re: C4 will only start with abs disconnected

Post by GiveMeABreak »

OK, here you are. Note this vehicle has ESP so does both ABS and the ESP jobs.

To be specific, this is only for a 2005 C4 DV6TED4 110 Without FAP and with Bosch 8.0 ABS with ESP
Image
Currycowboy
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Re: C4 will only start with abs disconnected

Post by Currycowboy »

Thanks Give me a break for the wiring diagram. Will check what abs module I have etc. Appreciated.
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GiveMeABreak
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Re: C4 will only start with abs disconnected

Post by GiveMeABreak »

Don't forget most of the wiring diagram component codes are listed in sections in our Wiki here:

https://frenchcarforum.co.uk/wiki/Elect ... ring_Codes