Gyrometer / Accelerometer sensor

[kingjafad]

Hi guys,
I am having a strange problem on C4 Picasso ABS (Mk2). I get the feeling through the brake pedal that ABS is pulsating the brakes at all speeds, in dry and non slippy conditions at all speeds. I have no ABS/ESP warnings and when i put Diagbox 9 on it, it claims to fail to communicate with ABS so i cannot find any faults via that method. I have a TOPDON diagnostic which does see the ABS module (still no error codes) and i can read the wheel speed sensors (all 4 are fine) plus a load of other info which is looking good apart from 'recirculation pump relay' never seems to be activated, and 'electrovalve supply relay status' faulty. I have had older 1.6hdi cars that have a dual ABS/Fuel pump relay attached to the front of the fuse box which caused that sort of error (albeit they also gave error codes too). On the off-chance that its the cause I found that 9801695280 (relay control module) is potentially a similar thing and cheap - but i cannot seem to find where it is located. The ones on ebay look clean so maybe inside the cabin? https://www.ebay.co.uk/itm/293032174796
I want to have my logic checked also - TopDon tool can see all the info - does that mean the module is communicating on whatever bus lines it needs to? If so why would Diagbox claim it cannot communicate with the ABS module? I have SEDRE and my RPO is 13476 which shows no clear sign of any relays in the wiring, but it also doesnt show any 12v power line from BSI to ABS module (just 2 powers from battery module) (My brain thinks the ABS module is good and communicating -aka the TopDon results, and that the module is pulsating the brakes like if ABS were actually needed aka i can feel it at all speeds when braking. So i am suspecting that the 'failure to communicate' with Diagbox is a symptom of why ABS module is thinking the car is skidding at all speeds?)
Hopefully that makes some sense.
Cheers in advance - Phil

[kingjafad]

Update #1 - So after some BSI resets that didnt clear anything, I removed the battery entirely to get to the negative and had a good look at all the Engine ECU connectors next to it, plus i removed the engine fusebox to have a good look at the connections to see if there was any cruddy signs, but nothing looked poorly in anyway.
I had a look behind the RH wheel arch liner but there isnt enough room to get to the ABS Module connector, I cant get to it from the drivers side of the engine as there is a large bracket doing nothing at all other than getting in the way and scrapping knuckles. The manual says to remove the scuttle etc but there doesnt seem enough room unless i break my arm to get to the ABS plug. Also the Electrovalve Supply Relay status is good again!
Anyway, I put the battery stuff back together and lo and behold Diagbox now can see the ABS module (ESP90) and I can control all the actuators/exhaust/inlet etc and they all audibly click when controlled and still absolutely no faults showing. But the brakes tell a different story - still pulsating (perhaps not as much as before but that may be my imagination). I am at a bit of a loss when all 4 wheel sensors show a coherent speed when driving around and yet the computer clearly believes its skidding.

[kingjafad]

Update#2
So I found that diagbox 7.83 seems to be more resilient with seeing my ABS module than 9.91 so I have taken screenshots from that.
I still have the brakes pulsating through the pedal at all speeds but still no fault codes showing up (although the steering angle screenshot would suggest otherwise).
The discs and pads are fine, the wheel speed sensors are fine (all 4 show graphs matching road speed and the minor differences of roundabouts).
A couple of things that I hope some experts on this forum may be able to help with are, what is normal on my screenshots?
Brake not pushed.jpg,

it shows 254bar (i expect 0) when i push the pedal a minor amount, it goes to 0, if i push more it registers that i am actually braking (brake pushed.jpg)

. I have ordered a new brake pedal switch which comes next week (only a tenner).
Then the esp gyroscopic info (esp transverse accelleration.jpg)

shows 0.5m/s whilst parked - i imagine this may be telling the ESP that i am skidding to the left or right? I am trying to find a way to calibrate that - i also cannot seem to find where the gyro module is on 2013 models (mk2) - on mk1 its under the centre console).
The Steering angle.jpg shows no issue with 'angle and speed' but under just 'angle' it claims to have a fault detected but no code? Any ideas anyone please?

[kingjafad]

Hi Marc, I saw you assisting many others on the forums with pictures of locations of parts etc. I have a problem with C4 Picasso B78 (late 2013) whereby ABS is pulsating gently through the brake pedal at all speeds of braking. This is under a no skid condition (all 4 wheel sensors show the same correct speed). There are no fault codes under Diagbox (other than a touch screen calibration file thing which i am convinced is unrelated). I did check Gyroscope readings under ABS and it showed a 0.5m/s drift when parked so i assumed it just needed calibrating, which i did and the drift went down to 0.3m/s when parked. I suspect its this gyro causing the issue but not sure where its located in the car to swap out. It seems common on pre 2013 C4 Picasso's to be under centre console between seats, but i also saw one of your posts on a recent C5 that post 2013 they generically put then under left seat? Before i dismantle the interior, could you possibly tell me, on a C4 Picasso B78 (Mk2 2013-) whereabouts the Bosch Gyroscopic sensor (Yaw,roll, accellerometer) is located please?
(I changed out the brake pedal switch already as a simple, yet unlikely cause but it was so cheap and easy, i thought it was worth a go).

Many thanks,
Phil

[GiveMeABreak]

There is an Accelerometer sensor in the actual Airbag ECU that sits between the front seats. This is used to detect front and rear impacts and adjusts the force of airbag triggering depending on severity of impact.

Then there are 2 lateral accelerometer sensors, one on each side of the vehicle that measure the lateral deceleration. The continuous data is sent to the airbag ECU which along with the main airbag ECU sensor determines the severity of the side impacts. However these should have nothing to do with any vibration of the ABS system.

The steering wheel angle sensor is housed in the steering wheel assembly and used by the dynamic stability system to determine directioon / intended direction and speed of turn. These need calibrating if they are ever removed, but I would expect a ESP warning and fault code if this or any other sensor were not operating correctly.

Regarding the vibration issue, the following is normal in case this applies:

Start the engine.
Drive, accelerate progressively and slowly until you reach 25 mph.
The dynamic stability control system ECU activates the recirculation pump for several seconds to test it which can result in the booming noise or the vibrations in the pedal bracket.

This is normal and will occur every time the engine starts and after the specific speed is reached.

Make sure the vehicle has the correct sized wheels and tyres as this can also affect ESP systems if they are not the sizes that were fitted at factory.

[kingjafad]

Thanks for coming back to me Marc. I didnt know about the 25mph test of the pump upon every restart of the car. I dont believe i hear it though when driving off and i have tried several times . I have used Diagbox to test the actuators under the ABS menus (the pump activated when i tested it parked up and it is quite loud as you say so i know what I am listening for - sounds like the old A10 warthog jet firing ). All the other valve tests (input and output) seem to click successfully albeit quietly. The ABS Gyro that I was referring to may be different to the Airbag ones you mention - The pictures/description i found online are - a little larger than a matchbox, white top with a bosch sticker, black base with 2 bolt holes, connector faces rear of vehicle.

. My thought process, if it is part of the ABS system, and its giving rogue readings, that if i unplug it I may get error codes but the ABS module wouldnt be seeing those readings and if i still get pulsating brakes, then its not the gyro at fault? (my techie brain trying to rule things out)
To give a little more history on this problem - ECO stop start had never worked since we got the car over 3 years ago, which i was reasonably confident was a slightly weak battery, the brakes were absolutely fine and no error codes. It got parked up and left for a week in Nov and when i next used it the brakes were pulsing at all braking speeds. Error codes were numerous, and not just braking related and my logic decided a poor battery (supposed to be 760CCA was reading at close to 380 - i tried a charger that was supposed to bring the battery back to life but it never got better than 380ish) was the cause of all this. I changed the battery and cleared the faults, ECO stop start worked again, and no faults came back. Then about a month later this pulsing brakes at all speeds started again. I put the Diagbox and TopDon ArtiDiag500 on it to find a couple of minor faults (driver door lock coherence, touch screen calibration file) but nothing brakes related. I did a BSI reset which made the pulsing brakes less pronounced but still there. A few times Diagbox couldnt even connect to the ESP90 ABS Module (but ArtiDiag always did). I checked the wheel sensors on graphs as i drove around and they are all reading fine.

[wheeler]

Just a though seeing as there are not fault codes logged, Are you sure you dont just have a distorted brake disc/discs? Might be worth getting it on a rolling road tester.
A quick check on service box & i cant see a separate yaw sensor listed for the B78 model, only the earlier ones. I would expect that if it thought there was lateral movement when the car is stationary it would throw up a fault.

[kingjafad]

Marc - I forgot to say I also checked the Wheel Size in the ABS config page and it was correct for my wheels/tyres, but a blooming good point. Thanks.

Wheeler - I did have the thought about rough/warped discs too but i only changed the pads all around in the summer and although the rear discs had some scoring didnt show signs of warping, they passed an MOT in Oct so not too bad. Also the pulsing is not the same as rusty/rough/warped discs (I have driven a car like that in the past) - What i feel on the pedal is definitely pulling and releasing. I have in a previous winter tested the ABS on a straight road and it worked well so i got a feel for normally what it should feel like with strong ABS pulsing - I am getting a much gentler pulsing but at the same frequency - its much more obvious when gently pulling up to a junction. I will, however get it on a ramp at the car club during this week and have a closer look all around in the dry with much better light

[kingjafad]

Just adding a few Diagbox pictures that may help narrow down the problem.
The ESP Gyro

after calibrating again (looks better to my uneducated eyes - maybe someone can tell me if those are good readings whilst parked).
The brake pushed gently

- the force increases with pedal pressure as i would expect
Steering Angle

-This is when parked, but when actually driving the bottom item (check of angle information by ESP) was showing no fault detected. Its only when parked does that change to 'Presence of fault' - but still doesnt flag a code! - Should i be seeing something instead of the top 3 items which have the '???' showing?

Thanks,
Phil

[GiveMeABreak]

That is the steering wheel angle sensor that I mentioned previously. That isn't correct, because at standstill with the ignition / engine on, you would be getting a reading (normally 0 degrees for dead ahead).

So it's not correct and neds to be calibrated I suspect. Again, the routine should be in the ESP ECU menu to do this.

[GiveMeABreak]

I've merged these threads (please don't start separate topics for the same thing), hence it's a bit all over the place. I haven't removed the post with the images as the near duplicate post contains different pictures.

[kingjafad]

Thanks for the pointer on the Steering Angle Marc - Ill give that a calibration tomorrow in the daylight - From what i have read, i drive 100m in a straight line and then stop but leave the engine running to do the calibration?
Also are you saying i should be seeing figures where i currently see '???' on the 3 top items. Apologies for the 2 threads, I should have pointed that original thread out when i contacted you.

[GiveMeABreak]

No worries, it just saves duplication of answers.

Yes, at standstill, the vehicle should be reporting the steering angle from the sensor and you should be able to see it change in real time as you move the steering wheel. To do this, make sure you are performing live tests. There should be one of the standard test parameters or you can select your own test for the steering wheel angle sensor.

[kingjafad]

So, I tried the Steering Angle Sensor calibration and I get the following every time i try - I have restarted the Car/Diagbox/BSI reset and it keeps saying 'Activation not possible' as its already started.

I did the standard measurements for Steering Wheel angle too and even when moving the wheel it didnt change the 780degrees or the '???' figures so I guess that nails it as being a faulty Steering Wheel Angle Sensor - (you were spot on from the start Marc ).
I am pretty confident pulling the COMM2000 or whatever it is now (did it on old 206's for airbag faults). The only part number i can find on the web though is for Mk1 C4 (966293780) and im not convinced the Mk2 is the same part?
Cheers,Phil

[GiveMeABreak]

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