C4 engine fusebox help needed

[admiral51]

Hi all
My 2005 C4 has been giving me a kicking again

I am 99% sure i now need a replacement engine fusebox just not sure which one i need so any help appreciated
I have already done the blower bridge ( not shown in pics) but the pictures show the fusebox before that bridge ( 15 months ago)
Something i did not pick up on was the fact that the inline 40 amp fuse is actually replacing fuse #13 the BSM
Well it has now melted that fuse and the connectors to the fuse holder are burnt black. I replaced the wiring and fitted a new inline fuse and even after a BSI reset i am getting strange faults, brake lights on all the time, wiggle the connector and brake lights off, air bag lights on and when it starts foot on brake pedal display goes blank and engine cuts out.Wiggle connectors so brake lights stay on and runs fine, except foot on brake pedal and wipers come on lol
VF7**************[VIN obfuscated, can be read by forum staff]

I can talk to the car with my clone Lexia but only via Diagbox which detects Vin but will not talk to all ECU etc, Lexia3 is other option but i need to input RPO number and i do not know where to find that, thought it was on sticker on drivers door pillar but needs to be a 5 digit number and cannot find one there ?
And is a replacement BSM as Citroen call it a plug and play or something above my pay grade
As always putting my faith in your capable hands to stop SWMBO going into a mega rage

[GiveMeABreak]

Part is 6500CK Colin. It doesn’t need coding or programming, but make sure you follow the battery disconnection and reconnection Procedure.

BSI Reset / Battery Disconnect / Reconnect Procedure

[admiral51]

Thanks Marc any ideas what a new one costs from Citroen, 2nd hand is going to be risky as it is a 14 yr old car, not going to waste good money, would like to get a new one and then chase back the wiring bypass issues
Can i be cheeky and ask if you know where the RPO number is located or does your status allow you to tell me what it is lol

[GiveMeABreak]

Hi Colin, your RPO is located on the driver door pillar where the tyre pressures are. Ignore the letters, just the numbers, and in your case your RPO is: 10371. Lexia is fine for your C4 as it's a 2005 model.

Part 6500CK is currently £290.14 inc. VAT from Citroen, although Eurocarcare have new ones in for £162 inc. VAT plus shipping:

https://www.eurocarcare.net/bulbs-fuses ... e-box.html

[admiral51]

Thanks Marc ordered from the link hopefully it will sort the issue out

[admiral51]

Talk about good service ordered part yesterday at 10 am arrived this morning at 9 am .
Fitted in under 20 minutes, BSI reset procedure followed and every thing works as it should
Taken fuse out from the heater blower bridge wire and it actually works as Citroen intended, no longer need to switch blower off before turning ignition on

I paid £170 ish for it all in, main dealers wanted just shy of £300 and when removed it had something rattling around in it.
Car has also been in for service at my local garage, £400 for oil/fuel/air and pollen filter, oil change and brake fluid change plus replacement of the near side inner steering rack joint that had been flagged as advisory for 4+ years on the MOT

Fuse box issue in first post happened 6 days ago, 2 days before it was due for its service so no fault of the garage, just hoped my re wiring had solved the problem but have a very happy SWMBO right now so thanks for all your help.

@Marc thank you so much for the help and advice, will be taking it for a drive tomorrow and then putting it on the Lexia again to see what faults if any are recorded.

Colin

[GiveMeABreak]

Excellent news, and I’m sure Mrs Colin will be equally pleased

[white exec]

Some history of PSA expecting standard-size blade fuses (0.25" blades) to handle high currents, and being unhappy delivering currents of 25A and more. Connectors and fuseholder contacts can overheat and oxidise, and finally burn out, often without blowing the fuse. For 40A and above, maxi fuses are preferable.

Some additional aftermarket in-line blade fuseholders are no better, despite often being described as 30A, some with thin wires attached, others relying on more 0.25" connections.

Blower motors are well-known for very high start-up currents. Even when running, full speed current can be 25A+, and start-up current much higher than that. It is good practice not to leave the fan speed control on High when quitting the car, to save wear on both IGN switch, connectors and fuses when the car is started up again. Far better just to turn down the speed to something lower for start-up.

[GiveMeABreak]

I think the more modern PSA heater control systems with climate control all start on low speed and then gradually increase - it's one of the reasons why there are so many failures over time where the air puller motor bearings get damp and start to seize. The low start up current is insufficient to get the fan turning, so bridging the plug to get full current is the only way to kick start it off. Ultimately the blower motor needs replacing. It's another reason (when I remember) that I switch the A/C off towards the end of a journey to allow the warmer air to dry out the internals of the air ducts and channels - to try and prevent moisture forming and collecting in the system.

But on your point about the current - I've just recently completed the rear light cluster earth modification on our C3 as the earth pin socket had started to melt and was giving us bulb out warnings randomly for all the rear lights (at least we know there are bulb warnings now). I had to bypass the earth completely and used thicker earth wire, direct from the light cluster common earth printed feed, direct to the body earthing point. PSA failed miserably here with insufficient earth wire thickness for the earth serving all the rear lights.

Pics here:

https://www.frenchcarforum.co.uk/forum/ ... lit=melted

[admiral51]

Well i am 100% sure it was the fusebox, have done 3 diagnostic sessions on it, both Lexia and Diagbox and everything is clear apart from P0136 downstream oxegen sensor that has a single intermittent fault at 1421 rpm @ 29 mph.
I cleared this fault, ran engine and then did another session and same fault even though car had not moved ??
Car has just been serviced and it is a little throaty compared to before but that may just be me lol

[myglaren]

[admiral51]

index.jpeg

Blinking awesome

[GiveMeABreak]

P0136: Downstream oxygen sensor signal: Coherence with the atmospheric pressure -
Voltage of sensor higher than 298 mv after 3 seconds in injection cut-off. (On releasing the pedal)
Immediate forwarding of the fault (so that's why the fault is coming straight back on).

Conditions of Activation of the Fault: Engine running
Conditions for disappearance of the fault: 3 starts and then stops of the engine without the fault being present.

Downgrade Modes:

• Deactivation of the adaptation of the downstream oxygen sensor
• Deactivation of the diagnostics on the catalytic converter

Symptoms:

• Switching on of the warning lamp possible
• Down-graded emission control

Suspect Areas:

• Check the continuity of the electrical line between the downstream oxygen sensor and the engine mangement ECU
• Check the heater element of the downstream oxygen sensor

[admiral51]

Thanks Marc for that explanation, and there was me thinking it was just a normal Citroen glitch that would disappear

Would i be correct in thinking that sensor is part of the catalytic converter and can be sourced for pennies

Will be taking it to work and back for the next couple of weeks ( 35 mile each way ) to try and give it a bit of run to get it up to temp rather than just running it around town and managed to get 46.7 mpg on the round trip today, my right foot is a lot lighter these days

Will leave the diagnostic check until the weekend, give it a proper chance to sort/throw up any faults .

Again thanks for all your help

Colin

[GiveMeABreak]

I'm just doing some editing on the Forum , but will get back to you later regarding this - the sensors can be tested on a scope or with live data on Diagbox - but I'll get a part number L8R for you.