Ignition Switch and Trip Computer problems

[JD01JD]

Hi,

I just bought a 1994 2.0 Turbo, series 1.5 I think.

There are a few issues — the ignition switch and the trip computer

With the ignition switch there does seem to be any accessory position — when in accessory all the symbols such as STOP, battery, coolant, etc show up just like they do in the run position without the engine running. The only additional warning light that shows up when turned to run is the catalytic converter one and the dials — petrol, oil level and temperature. The radiator fans also run when in accessory if the engine is hot enough or the AC is on. I'm just guessing this isn't normal??

Also the trip computer just displays ----'s. The previous owner said he "isolated the sports setting" and I assume he did this be disconnecting the speed sensor. I think the trip computer gets its information from this? I want to reconnect it but I don't know the first place to look! Anyone know where it might be disconnected?

Thanks,
Jordan

[Zaphod]

The trip computer is just waiting for you to set the time! and is behaving normally as are the rad fans. certainly that's how mine is

although I'd be far far far more worried about the 'isolating of the sports setting' as that sounds rather worrying!

Is the speedo working?
although I think all S1.5 cars had a cable speedo, but its possible some very late examples had an electronic one.

But.. the cable is in two sections, and between the two is an elsctronic speed sensor. However this feeds data to the ABS, Hydractive and Cruise ECUs so if you are not getting an ABS fault then its still connected. See if you can find out what the previous owner has done, and what the intial fault was as its often not that hard to make it all work as it was intended

This post has been edited by Zaphod on May 10, 2012 10:52 am

[JD01JD]

The time is set on the trip computer, all the other functions just display ----'s. I think the trip computer gets its information from the speed sensor so if its disconnected then it won't be able to calculate anything??

There was no fault with the suspension but I think the speed sensor was disconnected to keep it in soft mode permanently, and yes the speedo is cable driven so it still works.

It seems a bit stupid that I can't have the radio on without the radiator fans running...

[robertmnorton]

Hi, the cooling fans should only run if the engine temp trigger level has been exceeded, either one or two fans dependent on the level of exceedance and also at which speed they operate. This will also be the case until the temp level falls below the trip points after the engine is stopped regardless of key position. Mine will run for approx 10 mins after i take the key out, a rare occurence in the UK climate. If a/c is selected on and the selected temp is below ambient then one cooling fan will run at low speed with the key in accessory position. Also note the cooling fans are controlled by the auto g/box temp switch, which will also cause the fan or fans to continue operating after key removal. This last case would be unusual in temperate climates unless an auto g/box problem exsists. I have only noted this during a stop whilst driving the mountainous regions of Spain and France in the summer, and in all honesty am still unsure whether the g/box temp or evaporator temp was the actual cause, however it is normal.
The speed sensor is a primary sensor with regard to hydractive suspension and should show up as a fault on pre-check by flashing of the check light during ignition on and whilst driving.
robertm

ps. a correction to Zaphod's post in that the ABS does not use vehicle speed input from the transmission speed sensor and if yours is LHD it would be a single cable.

This post has been edited by robertmnorton on May 10, 2012 02:30 pm

[Zaphod]

QUOTE (robertmnorton @ May 10, 2012 02:05 pm) 

ps. a correction to Zaphod's post in that the ABS does not use vehicle speed input from the transmission speed sensor and if yours is LHD it would be a single cable.

Are you sure?? most ABS systems do have a speed input this is used to 'sanity check' the abs sensor readings to make sure they are realistic and to decide whech are giving dubius readings, the only one I can think of that does not is that on the SAABs which actually use an average of all the ABS sensor readings to drive the speedo!

I'd plug the speed sensor back in, it's found halfway up the speedo cable in the engine bay (on RHD cars, no idea on LHD cars) and find out what is worng with the supension as it sounds like its not working correctly if it was dropping into 'hard' all the time although IIRC if it detects a missing/faulty sensor then it defaults to 'hard' anyway. I think the seller was hiding somthing. If I had done somthing like that and came to sell the car I'd have pluged it back in. Assuming that all that was wrong with it was I did not like the way it behaved. Have 'comfort spheres' been fitted by any chance?

[xmexclusive]

Hi Zaphod

I am afraid that all the ABS documentation I have here suggests that you are totally wrong about the systems using of the transmission speed sensor.
Even Haynes gets this right for the XM Bendix ABS.
A quick look at the ABS wiring diagram will show that that the ECU has no input from the transmission speed sensor.
ABS systems of this age only use the wheel sensors for speed signals.
The system speed check mentioned is done by the ECU routinely checking agreement of the output from all 4 sensors while there is no brake application in progress.
If it is unhappy with the results of a number of these checks it switches the ABS out
and sticks the light on.
Every time you stop, switch off and restart the ABS resets and the light stays off until the ECU fails the running test again.

Edit note.

Have just looked up a few SAAB systems for similar age to the XM's.
Nothing special about the ABS.
At this time they used a early version of the Teves ABS as did the some Mk2 XM's.

John

This post has been edited by xmexclusive on May 11, 2012 11:45 am

[Zaphod]

You would have to look at the post '95 SAAB 900, that's when they started to use the ABS sensors for the speedo (quiet sensible really!) apart from that oddity its a quiet normal ABS system. Bu the post 95 900 and the 93 and I think 95 have no speedo sensor as a result

hmm.. the XM must be an odd one then, I know the XJ40 (Bosch 2e and teeves), 800 (various Bosch systems), Range rover(WABCO) and Omegas (Bosch again) ABS fails if the speedo drive fails. On those it does an overall resitance check on the sensors then when moving looks at the speedo drive both as a referance and to do the second check at 4mph or over and looks at the sensor signals, should one or more be off it shuts the system down. The reason for the speed referance is that if 3 out of 4 are bad it won't log the good one as being duff (cant say I ahve ever seen any more than one).

I would have to say that I can't ever remeber having any real issues with the ABS on the XM, beyond the current cars habit of throwing an error and it dissapearing on restart. The above cars I have had to play with on occasions and all will throw and ABS fault when the speedo drive fails.

This post has been edited by Zaphod on May 11, 2012 02:31 pm

[robertmnorton]

Hi Zaphod,

QUOTE

"it sounds like its not working correctly if it was dropping into 'hard' all the time although IIRC if it detects a missing/faulty sensor then it defaults to 'hard' anyway."

Again not strictly correct, only failure of a primary sensor will default to firm, secondary sensor failure will default to norm. This is explained in the Citroen technical training document module B7 for XM 1 & 2, and Xantia.
robertm

[Zaphod]

Fair enough. But I think I'd be wary of any deliberate disablement of the hydractive system

[xmexclusive]

On that last point I have to agree with Zaphod.
Sorting out previous owners enhancements and modifications are often a nightmare.
No way of knowing what they have done, why and is it the cause of the current faults.
Have a current one like that.
It is unlikely to have a very long life with me.

John