speedo not working

[borristherat]

first of all hi all as i am new to the forum.

all was working fine untill the other morning i started the car and both speedo and odo were not working.

the day before i had wired the tow bar but i think this is unrelated.

it is a 2004 2.0hdi.

took it to the local garage and they cant fix it and dont know whats wrong claimed they changed the speed sensor on the back of the gearbox.

20 years ago I used to be a vehicle electrician so thought sod it I can fix it, however, it appears I can't! I have tested for a voltage on pin 1 of the vss connector and have 11.2v; on pin 2 I have a good earth (0.1 ohms). Also shorting pin 3 and 1 quickly and intermittently causes the speedo to read a reading and the odo to work.

I was told that the way to test these sensors was to supply +12v to pin 1, -12v to pin 2 and put your multimeter negative lead to pin 2, positive to pin 3 and gently turn the gear. As you slowly turn it the reading on the meter should fluctuate between 12v and 0v on the dc range.

Assuming the above was correct I diagnosed the fault to be the vehicle speed sensor which I then replaced which produced exactly the same problem and readings as above so I bought another vehicle speed sensor and it still doesn't work.

I therefore assume this is not the correct way to test the vehicle speed sensor and there must be something else wrong within the circuit for all three sensors not to produce a reading on the speedo.

Any suggestions or help would be greatly appreciated.

[borristherat]

sorry all for posting a reply to my own post but with 25 views and 0 replies is the answere "take it to citroen?"

[BlueBlingo]

Firstly check the wiring to the tow bar

Do a BSI Reset follow this link: bba-reman.com/content.aspx?content=peugeot_bsi_reboot_process

I have attached some diagrams + wiring Legende for my 53 Reg 2.0 HDi Multispace 5 speed manual Gearbox. No AC, ABS or EPS on my Vehicle hopefullly it should be similar to yours.


Pin 1 on speed sensor is + 12V supply to sensor
Pin 2 on speed sensor is Earth
Pin 3 is `Pulsed` Output to Engine Management ECU

Engine management ECU measures pulsed output and transmits a multiplex signal to BSI thru wires 9000/9001(Can Bus)

BSI then Transmits a multiplexed signal thru wires 9004/9005 to Display, Display then shows corresponding speedo reading.
also tacho mileage incremented to distance traveled.


I believe you have proved your Multiplexing is working when you shorted the sensor wires.

Be careful if you are using multimeter around BSI Unit / surrounding area to get the correcr wires as a multimeter set on Ohms is sufficient to fire an Airbag or Pretensioner off

[borristherat]

cheers for that.

am i correct in assuming you can connect a battery across terminals 1 and 2 on the speed sensor and then should be able to measure your pulsed voltage on pin 3, with meter -ve on pin 2, when you turn the pinion gear.

for what reason would i reset the bsi and what is it?

you say shorting the sensor wires proved the multiplexing was working. do you mean by this that i have proved the circuit and so it must be the sensor?

lastly do you have any diagrams for a time machine so we can go back to the good old days when vehicle electrics were easy.

[borristherat]

next update.

booked it in to an auto electrician for monday. explained to him what i had done and he reckons shorting the sensor would have damaged the bsi unit!

i will keep you all posted as to what happens, in the mean time any more help or suggestions will be apriciated and thanks again for your help.

ps. what is a bsi? how do you know if its brocken?

[BlueBlingo]

next update.

booked it in to an auto electrician for monday. explained to him what i had done and he reckons shorting the sensor would have damaged the bsi unit!

i will keep you all posted as to what happens, in the mean time any more help or suggestions will be apriciated and thanks again for your help.

ps. what is a bsi? how do you know if its brocken?

The Sensor is not connected to the BSI,its connected to the Engine management ECU which transmits a multiplexed ( Pulsed signal to the BSI corresponding to the vehicle speed).

Did you disconnect the battery when you were installing tow bar or accidently shorted something ?

Try testing sensor and see what pulsed voltage you are getting out of it.
If so follow BSI reset procedure, follow the link and read up on it.

I don`t think you will have damaged the engine management ECU when you first tested the sensor . I think you have a tow bar related wiring problem causing the BSI to throw a wobbly this can also occur when disconnecting / reconnecting battery incorrectly.

[borristherat]

final update.

thanks to blueblingo for putting my mind at rest and helping me through the problem.

the problem was caused by me disconecting/ reconnecting the battery incorrectly when i wired the towbar.

this caused a fuse to blow within the BSI unit, citroen kindly diagnosed and corrected the problem for me this afternoon. £84 for replacing a blown fuse is a rip off but £84 for peace of mind is a bargain.

moral of the story is, a little bit of knowledge is dangerous and expensive. in future i will avoid messing with it myself i think. saying that £84 would not have got my towbar wired. the saga may continue....................

[steve valentine]

I didn't disconnect the battery when I wired my towbar

[borristherat]

I didn't disconnect the battery when I wired my towbar

lucky you. lol.

[steve valentine]

Not 'luck'