Display Light And Window Control, Please help

I recently acquired my third XM, a 1993 SEI turbo, with which I am very pleased, and I have just completed essential repairs to replace the brake valve and heater matrix. After running the car for 500 miles a few other little problems have come to my attention, as follows:

1. The yellow engine symbol on the dashboard display lit occasionally and now seems to be a permanent feature. My local Citroen garage has attemped an electronic diagnosis, but so far without success. The running of the car seems uneffected, but does anyone have any ideas what I could check and should I be concerned?

2. The driver's door control for the front passenger window was erractic and has now stopped working altogether, which I assume is a faulty switch.

3. When drawing to a hault there is a momentary sensation of 'give' in the brakes, which appears to be coming from the front kerbside wheel, possibly a slightly loose or sticking shoe? The brakes otherwise are excellent.

With thanks in anticipation and kind regards,

Matthew T.

Hi Matthew,

What exactly do you mean by 'without success'? Isn't the computer able to connect? If so there are two possibilities: either the ecu is faulty (unlikely) or the power supply to the ecu is faulty. The ecu must ahve a sound power supply and a sound earth to work properly. A check with a multimeter on the correct pins would possibly reveal a fault. If not, what are the symptoms of the computer connection?

You may be right about the window switch.

Although there are some reports of ABS systems giving trouble I'd start with the basics. Remove each of the front wheels in turn and bleed the brakes very well. After throwing away the first few tens of cc's of LHM put the bled LHM back in the header tank. This will allow you to bleed the brakes quite comprehensively without throwing too much LHM away.

Let us know how you get on.

Cheers

noz

What exactly do you mean by 'without success'? Isn't the computer able to connect? If so there are two possibilities: either the ecu is faulty (unlikely) or the power supply to the ecu is faulty. The ecu must ahve a sound power supply and a sound earth to work properly. A check with a multimeter on the correct pins would possibly reveal a fault. If not, what are the symptoms of the computer connection?

You may be right about the window switch.

Although there are some reports of ABS systems giving trouble I'd start with the basics. Remove each of the front wheels in turn and bleed the brakes very well. After throwing away the first few tens of cc's of LHM put the bled LHM back in the header tank. This will allow you to bleed the brakes quite comprehensively without throwing too much LHM away.

Let us know how you get on.

Cheers

noz

>You may be right about the window switch<
There is an interconnection between the laft and right door switches. Make sure both are in working order.

Mwt,

ABS ECU can have a cause you described, I had it on my 1993 SEi V6, but it was quite scary... it was releaseing for a good turn of a wheel!!!!

I put a 1991 ABS ECU, marked ABR and is useually black, third ECU from front on left side, and the problem seemed to go away..

I've also known a Peugeot 405 some 10 years ago that was dooing the same, releasing the brakes, it was an Mi 16 model, on a 1992 plate, the dealer changed the ABS ECU and the problem went away on that car...

It has however, been sugested to me that it could be also on over active sensor, but I dont personally beleve this with changing the ECU on my car in question..

Regards
citroenxm

Hi MTW,

I sadly only have room for one XM (shame) but it is a 1993 2.0 turbo like yours.
Mine suffered from low power and the engine light would come on above about 2500 rpm. This was down to the turbo not boosting and subsequent rich mixture sensed by the lambda sensor. Luckily mine was easily fixed as a lever had become disconnected on the turbo.

If your power is ok then the turbo is probably fine, they are very simple beasts. With that eliminated it means that the ecu is possibly getting a duff signal. This could be either:

1 Mixture too rich
2 Bad connection to the Lambda sensor
3 Duff lambda sensor

I am sure that someone will know how to test the sensor I think it is either a simple resistance measurement or a voltage. I expect this post will jog someone's memory and they will give some hints here. Otherwise a competent garage with the correct diagnostic equipment should be able to help. I don't mean just plugging in to the ecu, there are more complex diagnostic machines out there which can look at CO, Lambda, mixture, injection and ignition they put leads all over the car to pick it all up but the operator needs to know their trade.

Best of luck

John

Dear noz, citroenxm and John,

I am very grateful for the prompt and helpful advice provided in response to the three problems described. As I understand it the following action is required:

1. In relation to the engine light, check the ecu, sensor and connections and the mixture adjustment (my local Citroen garage could not complete a diagnosis, due I understand to time constraints and identifying the correct equipment).
2. Repair or replace the window switch.
3. Bleed brakes and if not sucesful, check the abs ecu and sensors.

I shall let you know the outcomes in each case.

With thanks again and regards,

Matthew T.

MWT,

Bleeding of brakes in my experience is NOT needed, the brakes will either WORK or NOT work, the problem is defenatly electronic and not a hydraulic issue..

Window switches not worth fixing, easyer to simply replace..

Regards
citroenxm