MOT Result & Fault

[steve_earwig]

It would be easiest for you to post it on its own thread (under engine and mechanical), then we can have a squint and shift it across.

[johnboy]

Yeah sure will do that.

[FlySpeck]

I don't think HPis came with dpfs, no diesel you see. Unless it's a ppf...

Looks like it's got loads of sensors on the exhaust though, did you get the latest codes read?

Whoooooops looked at it and saw HDI and not HPI - in fairness I was tired (pished) lol

[DaiRees]

Hi Dai,

Did yours go into limp mode from that downstream sensor? mine seems to be doing it when your on main roads where you have to accelerate more or like up a hill or instance.

Ill get the codes read and see what it comes back with.

Is it true that sensor is plugged in under the hand brake area? if so i may check this as someones been under there before as its all loose!!!

Nah never had limp mode mate (oh fek, that's tempting fate innit!!!)

The plug for that sensor is in the bay at the back of the engine, so it's not the one you're thinking of. There's so many bloody sensors on these things though that it could be anything....

[johnboy]

Yea tell me about it!!!

Im thinking now it could b a lambda gone? hmm im just clutching at straws, ill find sum1 to scan it monday and let you know my findings.

cheers

[FlySpeck]

ok now my head is screwed on lol

The pre cat o2 sensor measures combustion gases before catalytic treatment when the engine is warmed up and in closed-loop mode, meaning fuelling is altered according to the primary o2 sensor readings, its trying to achieve a lambda reading of 1.0

The post cat o2 is checking the cat is working, and you can use a laser temp gun to check temps across the cat, should be around 700oC at the front end, going down to about 450 at the outlet end, but find out the specific figures for your model & engine first. Your cat must be ok as the car passed the emissions test for the mot eh, so the second o2 sensor could be faulty as the primary one would cause misfuelling and emissions failure or cat overheating.

just my tuppence worth, my money would be on the second o2 sensor or its wiring, a code scan will pick that up. Best place to start on most faults.

[johnboy]

Thanks for the replay dude, that does certainly make sense i guess.

Is there any way i could check this? where would i find it and where is it plugged into? Are they easy to replace yourself?

Cheers

[johnboy]

Looking at the D8 Fuse diagram there is a 10a fuse for the lambda sensor? Do the D9's have these too? if so could it be a blown fuse causing it not to work?

thanks

[FlySpeck]

yah pretty much guaranteed to have them too. they have 2 or 3 wires (depending on seperate heater supply or integral shared supply between sensor and heater) and need either plugged in or spliced in (if its a non oem aftermarket bosch one) - usually white, black and brown, check the wiring diagrams for your car if you buy a non oem one to make sure the colours match up with yours (in wire function i mean, if the colours are not the same)

testing that fuse would make sense, if the heater is shorted out it will blow again, but that would be expected and point to a very faulty sensor.

They also are screwed into a pipe coupling on the exhaust after the cat or straight into the cat's side, and are the very devil to remove sometimes. They get very very hot, and live in a harsh environment so they tend to sieze in after a while. Looks like a wee spark plug screwed into the downpipe etc, you will know it if you see it, just need to follow the exhaust from the manifold back when its on a ramp etc.

aftermarket ones will be cheaper than oem and need no recoding or anything, just need wired up correctly and screwed in tight, plug and play! Dont use nylon block or scotchlock connectors to join the wires to the new one, the heat there will annihilate anything not very very heat proof, so use ceramic connector block (available from electrical wholesalers) or other high temp silicon jacketed crimps.

[johnboy]

I cant seem to find the fuse looking at a D9 layout? do u have one on urs or where in the fuse boxes i mite find it?

cheers

[johnboy]

Ok i managed to find it in the book, if you have a look here you will see fuse 15 in the engine compartment controls the oxygen sensor?

http://public.servicebox.peugeot.com/dd ... _en_us.htm

I havent yet checked this fuse myself but as it controls the o2 sensor - ignition coil - wiper etc... so surely if this fuse was blown i wouldnt be able to start my car would i ? and also which o2 sensor fuse is this? is there one for the rear o2 sensor?

My mind boggles!! lol.

[FlySpeck]

lol its a pain eh.

ok, i cant find the page you refer to, its the main pug page that comes up, but a rear o2 sensor (or the front one for that matter) would normally not be set to trigger limp mode on most cars as it is not critical in the ecu strategy map but pug might have seen fit to make it a critical level sensor.

Unfortunately my pug knowledge is deep on diesels but light on petrols, so although I have had similar problems with a subaru and a golf VR6, neither went into limp because of the O2 sensor failing, but an o2 sensor error can be from a failing MAF thats reading airflow wrong and over or under fuelling, that will triggger an o2 sensor "out of range" error but only a truly faulty sensor will trigger any "open circuit" or "short circuit to ground" or "signal implausible" type code, and like I said, limp mode is not a usual strategy for the ecu to employ when this happens as the o2 sensor reads the result of combustion and then the injector duty is altered (adaptive fuel trim) but only when the coolant temp is over 50oC as before that the o2 is ignored (open loop mode)
.

[johnboy]

Yer it is!

By the way i got the codes read today, i started a new thread on them. Basically it came up as

Fuel pressure low
Fuel pressure regulator fault
oxygen sensor fault.

i just wondered tho if the o2 sensor was faulty wud that bring up the other 2 faults with the fuel as it goes into limp mode etc?

thanks for the info so far fly

[FlySpeck]

heh no problem matey!

Now, I think the o2 error is the red herring, and the fuel pressure the real one.

The fuel pump may be failing and dropping below the pressure regulator minimum supply, or the regulator itself could be faulty, either of which could trigger a rail pressure sensor error. (causing the first code, as the injector supply rail is the first place where the fuel pressure can be measured)

Low fuel pressure could lead to underfuelling and pinking, maybe causing the o2 error - as theres too much unused oxygen in the exhaust gases.

On the petrol engine I would expect 7 to 15 psi max, but others may know better and you still need a garage or the tools to check it.

[johnboy]

Hmm.... Sounds like its possibly a few things then? sounds expensive too! haha.

Ive had the regulator replaced just b4 xmas so hopefully it shouldnt be that ? im reli hoping its not the pump itself.

What would i need to ask the garage to check? do u think sum of these faults are caused by something else?