Gasa XM 2.1 "Prestige"

[Gasa]

...I didn't read the error codes,I didn't make the device you have, I don't own Lexia.
I changed all the bulbs in the instrument panel, and the one for ABS was faulty, and I also replaced the valve cover gasket.

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[Dieselman]

You are doing a great job and as you have found diagnostic equipment is a nice to have time saver, but not absolutely necessary.
A blink code reader is cheap to make and will allow error codes to be read/cleared and some testing and programming on some petrol Ecu's.

Imho, it is better to have a generic understanding of how the electrical components function and the feedback the Ecu is expecting to see. You will then be able to formulate a test for any device.
An oscilloscope is more useful than Lexia, for testing high frequency items, such as crank sensors, speed sensors, Lambda sensors, though one can normally get by just with resistance check and voltmenter.

What is the red liquid on the injectors, or is it just diesel on top of rust?

[Dieselman]

It's not hydroactive, it's a regular system, if it was hydroactive, I wouldn't have taken it because it's complicated.

The 2.1Td with manual gearbox you have is one of the best Xm to own, but after you have finished working on the car you have, I think you will regret not going for the Hydractive version.
The hydractive system is complex, but not complicated and is generally reliable. If you can understand and fix the ABS system you can deal with the Hydractive system.

[Gasa]

Electronics is my weakness, I don't understand myself very much, the hydraulic system is even more cluttered with various wires and sensors.

There aren't many XMs here, this one hasn't been driven since 2010, it's only been started occasionally, so there are a lot of little things around it to fix.
I noticed that sometimes, the bulb for the heater doesn't light up, I checked the heaters and they get power but the bulb doesn't light up on the instrument panel, what turns on the bulb and where does it get the signal to turn it on and off.

[Dieselman]

The glow plug relay is mounted on the front of the battery box, but I suspect the issue with the lamp is the dashboard edge connectors have cracked solder joints, which need re-soldering.

Nearly all the electronics used on modern cars is digital electronics: the switch, signal, sensor, is either on, or off...the voltage is either high, or low.

An Xm is a great place to learn automotive electrical systems because it is pretty simple, but a lot of it.
The hydractive-2 system uses digital signal inputs (on/off) from the body attitude sensor, steering sensor, speed sensor, brake pressure switch and a variable voltage (analogue) signal from the accelerator sensor, to determine whether the Electrovalves should be switched on, or off.
That's it...nothing complicated.

Hydractive-1 is very similar, but the speed sensor is analogue, the same as your ABS sensors.

Take a look here at Gabor's excellent XM Series-2 circuit diagrams from the Self help files. to check the wiring for your glowplug lamp.
download/file.php?id=9711

The glowplug lamp is covered in both the 2.1 engine section and the warning lights section.

Yellow 15 pin connector, Pin-1 = +12v from glowplug relay, Pin-15 = Gnd.

An incandecent test lamp is often better than a Dmm for testing circuits, as it applies load, due to having lower resistance.
If there is a poor contact a Dmm, or LED/LCD tester can show full voltage present as the required current is so low.
You want some cheap test lamps in low wattage (approx 0.8W), medium wattage (5w), high wattage (55w), for testing different circuits and situations.
Use low wattage lamps on electronic circuits, high wattage lamps for testing Gnd, feed to starter motor, etc.
Led test lights can be useful for monitoring quick acting sensors, where a Dmm is too slow to react to the changing state. e.g opto sensors used in the Hydractive systems.

[Gasa]

..thanks for the detailed answer.

[Julianw]

Slightly off topic i know, but when you describe the test lamp vs DMM pros and cons, it strikes me there is a need for a piece of test gear like a power probe, with a switchable load on the circuit under test, to offer the pros of three test lamps but in one box, and using something more rugged like LEDs. DMMs are specified as to their sensitivity i.e. 20,000ohms/volt, but there's not much choice between different models - all place very little load on the circuit under test.
Is there a piece of test gear commercially available that can vary the load on the circuit under test? And if so, what is it called?

[Dieselman]

Is there a piece of test gear commercially available that can vary the load on the circuit under test? And if so, what is it called?

Expensive...

[Dieselman]

A decade box is a switchable resistance load for electronic circuits, but there are very few situations were it would help for automotive fault finding.

One already has the device to be powered and is usually trying to diagnose why it isn't functioning, whether that be a result of no power/Gnd, or the device is faulty.
A decade box is meant to be a substitute for a device. This could be useful for system designers, or circuit board repair.

It would be possible to sustitute the open circuit Abs sensor, Gasa has, with 1,100 Ohm resistance, and see if the Abs system passes the static test, but a resistance check has already proven the sensor is open circuit, so we know it is faulty.

[Julianw]

Thanks, that's interesting!