S2 Xantia speedo very intermittent

[rizla]

Hi,

I'm writing this on behalf of a friend who has a 1999 S2 Xantia 1.8 16V petrol which is misbehaving and upsetting him. Since I have to work with him, it's best if he's kept happy.

His speedo stopped working a few weeks ago, intermittently working for a few seconds, needle sometimes giving the odd jerk at times too.

We changed the speedo sensor in the transmission using a brand new one from GSF which a garage has now changed again with no change to symptoms either time.

He removed the instrument panel and checked for poor connections and dry joints but found nothing amiss.

I've recommended he check continuity of the 3 pins in the plug thatg connects to the sensor. I know one pin is 12V supply, one is ground and one is signal. However, I don't know where they go to. Does anyone on here?

Google searches give answers varying from the wiring going straight from sensor to instrument panel; from sensor to ECU; from sensor to some control box behind the glovebox that does magic and sends a control signal to the speedo stepper.

Anyone know for sure what the situation is, and does anyone have a wiring diagram? (incidentally one post on here mentioned pin 5 of a red connector on the back of the instrument panel being the receiver of the signal from the sensor, but his connectors are green and something else, no red ones.)

[RichardW]

Is the odometer still counting? If so, then this rules out the sensor or the wiring. Xantias do not have the box behind the glovebox, this is a 406 thing only. Most likely is that the spring pins that transfer the signal the speedo head need cleaning - this is rather a delicate operation involving stripping the PCB out - Jim describes it in this thread: Xantia speedo

[rizla]

Hi, thanks for the reply, I've confirmed that the odometer is not counting.

Do you know if the sensor signal goes to the instrument panel, or does it go to the ECU which in turn controls the speedo? Or are both ECU and speedo directly connected to sensor signal?

[c.morewood]

This may help
viewtopic.php?f=3&t=40038&p=321895&hilit=speedo#p321895

[rizla]

Hi, thanks for the link but he's already successfully removed the instrument panel and speedo unit and found nothing obviously wrong. We'd like to ascertain that the speed sensor signal is arriving at the instrument panel, but without knowing the wiring situation, it's not going to be easy.

[Hell Razor5543]

I am NOT knowledgeable on the Lexia, but I wonder if it can show how fast the car is travelling. If it can, then (if you either have a Lexia or access to one) you can see if the speed sender is working.

Where is the car in question? You could look on the Lexia location map.

[Mandrake]

On a petrol manual Xantia I don't think a Lexia can show the actual road speed signal that is sent to the speedometer, as I don't think that goes anywhere near any ECU's, it just goes from sender in the gearbox to the speedo in the instrument panel. (Given that manual gearboxes don't have ECU's...)

You can display the road speed from each wheel sensor on the ABS ECU with a Lexia but of course those signals don't go to the speedometer.

On a Series 2 automatic you can read the road speed measured in the differential with the Lexia albeit in drive shaft RPM that then has to be converted to mph, however I'm not certain whether this same final drive speed sensor that the gearbox uses for its own purposes is the one that's also used to drive the speedometer...