Peugeot 206 auto. Speedo goes off and lumpy gear change

[oldbill]

2003 (multiplexed) Peugeot 206 automatic.
For a few weeks its been randomly loosing its speedo accompanied by lumpy gear shifts. Got more frequent so ordered and fitted a new output shaft sensor for the AL4 autobox but its made no difference. Any ideas?
oldbill

[ozvtr]

I have seen this before but I cant remember what the fix is.
You will need to supply your VIN and ask Marc very nicely if he can supply a circuit diagram.
Basically, the speed sensor gets its power from the BSM and an earth from the engine ECU common. The speed pulses from the sensor go through the BSM to the engine ECU which calculates the speed and sends it on to the CAN BUS. Both the instrument cluster and the auto box use the speed info, on the CAN BUS, to do their "thing".
You should have power (12V) on pin 1 of the sensor and ground on pin 2 of the sensor. You also need to have continuity from pin 3 of the sensor to the input pin of the engine ECU.

Update: I found where I saw that post.
https://citroenc3owners.com/viewtopic.php?t=5497
You may need to cut and paste they don't allow linking.
The final solution was just to erase the error code!

[oldbill]

Hi ozvtr Thanks for the reply and the link. I'm still getting nowhere with this problem, I was so sure it would be just the speed sensor but unfortunately not. Biggest problem is lack of information, The 'Haynes' manual for this car has quite good wiring diagrams but only for the manual version, I also have service documentsl for the AL4 autobox but its all mechanical info.

The speed sensor is located on the AL4 autobox just above the output shaft, its a two wire sensor with a resistance of 1.75k between the wires. When I turn on the ignition there 1s 2 volts dc present on both wires (Measured agaist -ve chassis) I dont know if this is correct. I have tried to establish if the fixing screw forms any sort of ground or earth point but i dont think so. I dont have any sort of portable oscilloscope but with a test meter set to AC and the car moving there is a 2.5 to 3v ac voltage across the wires so I guess its producing some sort of waveform. The sensor wires are brown and white, they go through the harness to the engine ECU, connector is perfect with no sign of corrosion or even tarnish but I cleaned it with alcohol anyway. Without a diagram or info its hard to know what path to follow , I've pushed pulled and proded the various sections of harness but its made no difference. Right now I'm working my way slowly and randomly through the various plugs, connectors and fuses looking for tarnish or corrosion. Dont know what else to do.

Thank you for the reply,
oldbill

[wheeler]

The speed sensor is located on the AL4 autobox just above the output shaft, its a two wire sensor with a resistance of 1.75k between the wires.

Think you may be looking at the wrong sensor, the road speed sensor has three wires & is located on the diff of the gearbox, its hall effect so you cant really resistance check it.
Should look like this > https://www.ebay.co.uk/itm/255138015912 ... 1&mkcid=28

The sensor is fitted here where this blanking plug is

[oldbill]

Hi Wheeler, the speed sensor or its circuitry was my number one suspect but I replaced it and it made no difference. I'm still very suspicious of it. I had expected it to be a 3 wire sensor with voltage (either 12v or 5v) on one wire, signal on the next and ground on the last, or a similar combination. In fact it's a 2 wire sensor with 1.75k resistance across it. With ignition on there is just 2 volts on both wires which seems strange, my best guess is that there's just a coil of wire as an inductor in the sensor with a magnet or magnets on the output shaft. As far as I can see there are just 2 sensors on the gearbox, one on the input shaft side and one on the output shaft which is the one I changed. With the passenge side wheel and 'plastics' removed its about halfway up the box on the bulkhead side. I'm 99 % sure its the right one but I'll double check in the morning. Crazy thing is the car will somtimes drive perfectly for an hour or more then suddenly no speedo and crazy gearchanges!
Thank you for the reply
oldbill

[wheeler]

Can you post a pic of the sensor you replaced?
The road speed sensor should be in that location & should be a 3 pin plug. Ignition live, earth & pulse output. All 12v & the signal is a square wave output.

[oldbill]

Hi Wheeler, decided to take a day off the thing today, Ill pull the wheel tomorrow and photo it. If you look at flea bay 315026840158 thats the sensor, plug varies with model year but just 2 wires. brown and white. The input shaft sensor is similar but shorter. I have Lexia /planet on an old win xp laptop. not been used for years but if I can make it work it might shed some light.
oldbill

[wheeler]

Thats definitely not where the road speed info comes from, if it has a road speed sensor then its fitted where the blank is in the pic above, if your gearbox has a blank there then the road speed info comes from the ABS system.
I think the sensors you have changed is an internal speed sensor for the gearbox speed not vehicle speed.

[oldbill]

No ABS on the car so speed sensing has to be from an output shaft sensor on the gearbox. I could only find two sensors, one on the input of the box and one right on the output shaft which is the one I changed. To be honest I expected 3 wires :-
12v
speed signal as a square wave
earth
which is exactly what you describe, instead I have two wires with about 2v on each with the ignition on. I think what I need to do is clear the passenger wheel arch again together with the battery, battery tray etc so I can see the whole area clearly. wont take long and if theres another sensor I'll find it.
oldbill

[oldbill]

FIXED !! It was electrical 'noise' from a defective ignition coil pack. It seems that rubbish electrical interference from the pack was blocking or confusing the normal communication between the ECU, BSI, Sensors etc. Speedo is now working fine and gear changes perfect.
ozvtr and wheeler, this was a horrible fault to trace and its been great to have u guys to throw ideas back and fore with, many thanks.
oldbill

[wheeler]

Strange but not unheard of. A couple of times I've had a defective ignition coil causing wiper faults on a Xsara Picasso, Also had one corrupting a crank sensor signal causing a non start, only picked up with a scope.

[ozvtr]

From your initial post on the sensor, that's the output speed sensor for the AL4. Not connected to road speed.
You didn't say what engine you had. If it's a TU1 or 3, there is a green and yellow wire attached to the coil pack retaining bolt on the right hand side (as you look at it from the front). This is a shield for the coil pack wires. If that's broken that will explain part of your problem.

[oldbill]

Hi ozvtr,
Car is an 03 plate with a tu3 1.4i engine, there's no abs so nowhere else any form of speed reference signal can come from except the output shaft sensor on the AL4, there wasn't the slightest dought in my mind so I just ordered and fitted it. (silly me, its a Peugeot!). There's no green/yellow wire but could have been lost over time. Each fixing hole in the coil pack has a metal anti crush ring right through so earthed well through the bolts but I may add a wire anyway. It was a blighter of a fault and for me its been a 'wake up' in that I should run diagnostics first not just guess. When I eventualy ran Peugeot Planet there was no pinpoint diagnosis just reference to the missing speed signal and lack of speed signal 'coherence' however also multiple reference to 'missfire'. There had been no missfiring but I had spare spark plugs so changed them anyway, in doing so I noticed the left side ( belt side) of the coil pack was noticably warm, engine had been off for at least 15 mins so must have been very warm or hot when running. After some more 'faffing about' I bought and fitted a new coil pack and everything is now perfect. Looking at the old coiil pack there are two distinct rectangular shapes in the potting compound so I guess these are two individual coils and one is not as it should be.
oldbill