Lexia questions

[stedmancinques]

If I buy a Chinese Lexia, will it tell me if an ABS wheel sensor is faulty? Although there are no problems at the moment, within the first year of owning the car, three of them failed, both fronts and a rear. That was eight years ago, and it can only be a matter of time.
Also, at least one instrument bulb has failed, inevitably the one that illuminates the fuel gauge. Will it be airbag and steering wheel off to replace them? If so, will there be any resetting to be done? And would the Lexia do that?

Subsidiarily, if I get as far as the instrument cluster, is it a whole lot extra to get to the heater matrix?

[stedmancinques]

Apologies, I've found the thread on heater matrix replacement, in which Citrojim answers all my questions on that topic.

[wheeler]

No diagnostic computer will tell you if a wheel speed sensor is faulty, it wil only tell you there is a fault with the circuit. You can then either guess that the sensor itself is faulty or you can do some further checks & diagnose it properly.

[VertVega]

If I buy a Chinese Lexia, will it tell me if an ABS wheel sensor is faulty? ...

If there is an ABS error (permanent/intermittent) then my Chinese Lexia shows a message as seen
in below printscreen which I saved during the first global scan.



I am happy that I bought it

[xmexclusive]

The stored ABS fault codes differentiate between sensor failure (static resistance) and sensor malfunction (dynamic signal). I cannot believe that the Lexia is so crude that it is programmed to treat these as a single fault.

John

[wheeler]

If an inductive speed sensor goes open or short circut how can Lexia possibly tell where the circut is open or shorted ?? it could be anywhere from the ECU connector right up to the sensor. Could even be an internal fault in the ABS ECU itself.
The fault shown in the screenshot above doesent tell you that the speed sensor is faulty, It is only saying that the ECU is not seeing the speed signal, this fault could also be flagged up by a broken pickup ring on the driveshaft or a poor connection at the sensor plug.
So I still standby my statement NO diagnostic computer can tell you if you have a faulty speed sensor just by plugging in & reading a fault code.

[mongoose100]

The Lexia will however, show you what each wheels rotational speed is...

That should tell you exactly what wheel to look for IMO

[xmexclusive]

Hi wheeler

You seem to be unaware that the typical ABS ECU continuously checks and stores quite a number of different fault codes. Some faults are recorded on startup some on running. These include for each sensor, Resistance, Signal from sensor, Continuity of electrical circuit between sensor and ECU.
Other codes deal with the hydraulic block components and ABS light system.
It also differentiates between permanent and temporary faults.
Many of the temporary faults recorded are cleared when the ABS does a startup test so the Lexia or code reader is best used before switching off the ignition. Equally when component replacement is done it is best to clear the ABS ECU as to use normal running to purge its memory of the more serious intermittant faults can take some while.

John

[wheeler]

The Lexia will however, show you what each wheels rotational speed is...

That should tell you exactly what wheel to look for IMO

I totally agree with that statement, but it still will only show you that there is a fault on a specific wheels sensor circuit, it doesent tell you that the sensor is faulty.
Xmexclusive: im pretty well up on how lexia & abs systems work and your right the ecu does check lots of different values from each sensor but for example when it checks the resistance its checking the whole circuit from the terminals in the ecu connector right up to the sensor so if lexia reports an open circuit on the RHL sensor circuit how can it tell if its a broken wire in the loom somewhere or a faulty sensor ??

[stedmancinques]

I'm sorry if I started an argument. When the previous three ABS sensors failed, Simon at the independent Citroen Peugeot garage that I use plugged in a hand-held fault code reader, and was able to tell which wheel circuit was faulty. In each case replacing the sensor cured the fault. I did the fronts myself, but the rear was too inaccessible without a post lift.
I just wondered if a Lexia would give me the same information. Having raw data, and knowing how to interpret it, are, of course, two entirely different issues.
Cheers to all.

[xmexclusive]

Hi Wheeler

I agree with you that the open circuit case requires the full wiring to be checked. With intermittant faults though the codes differentiate between resistance test failure and sensor output problems.
With resistance failure I find that unplugging the sensor and replacing it with a 1.2k ohm resistor quickly sorts out if the fault is in the wiring or the sensor. Pre Lexia reading the raw codes from the ABS ECU often saved a lot of time in pinpointing what to check but was seldom used.

John

[cachaciero]

The Lexia will however, show you what each wheels rotational speed is...

That should tell you exactly what wheel to look for IMO

I totally agree with that statement, but it still will only show you that there is a fault on a specific wheels sensor circuit, it doesent tell you that the sensor is faulty.
Xmexclusive: im pretty well up on how lexia & abs systems work and your right the ecu does check lots of different values from each sensor but for example when it checks the resistance its checking the whole circuit from the terminals in the ecu connector right up to the sensor so if lexia reports an open circuit on the RHL sensor circuit how can it tell if its a broken wire in the loom somewhere or a faulty sensor ??

cachaciero

[wheeler]

Hi Wheeler

I agree with you that the open circuit case requires the full wiring to be checked. With intermittant faults though the codes differentiate between resistance test failure and sensor output problems.

I'm sorry but intermittant faults can be related to wiring aswell. Wiring insulation can be gradually chaffed away & cause for example bare wiring to touch the body when going round corners/going over bumps a certain way etc. Also a cracked pickup ring can cause intermittant faults if it slips in the CV joint at certain speeds.

With resistance failure I find that unplugging the sensor and replacing it with a 1.2k ohm resistor quickly sorts out if the fault is in the wiring or the sensor.

Thats kind of what im saying, You still have to do further checks after getting the fault codes like fitting a resistor. A fault code wont tell you 100% that the sensor is at fault. I know most of the time it will be the sensor thats the problem but it's not a great idea to just guess unless you have plenty of money to throw st the car.

[DHallworth]

Last time I used my Lexia on a Xantia HDi Exclusive it actualyl told me the EXACT sensor that was triggering the ABS warning light on the dashboard.

On the screen that is shown above, press the Enter key again and it will give you a note of the sensor that is causing problems.

David.

[wheeler]

Last time I used my Lexia on a Xantia HDi Exclusive it actualyl told me the EXACT sensor that was triggering the ABS warning light on the dashboard.

On the screen that is shown above, press the Enter key again and it will give you a note of the sensor that is causing problems.

David.

Yes Lexia will tell you if there is a fault on eithr the front left, front right, rear left or rear right wheel speed sensor circuit but there is no way it can tell you 100% (just by reading a fault code) that the sensor itself is faulty. An inductive sensor is just a coil of fine wire wrapped round a magnet & for it to (electrically) fail it would either be open circuit, short circuit, high resistance or low resistance. When Lexia does a check on each sensor circuit There is no way it can differentiate between the short circiut, open circuit, high resistance or low resistance being in the actual sensor or in the wiring that connects the sensor to the ECU.
The fault in the screenshot above could be replicated by cutting the wire leading up to the sensor whilst driving then repairing the wire once you stop. Lexia would throw up this fault as the speed sensor signal from whichever particular wheel would be absent & it would tell you excatly which wheel circuit it was. You would get the same fault code coming up with a faulty sensor depending on how it failed.