General approach to repairs and diagnostics Diagbox question

1) Whats the 'work flow' for using the diagbox?? I

jmmj wrote: ↑Sat Nov 21, 2020 6:46 am Now the information offered in Diagbox is basically just the code with little or no indication of 'go change x part'...

For example, from several codes i know i have a dodgy brake switch. I also have an error code D308:

"Communication error between the automatic gearbox and the engine management"

Why is there no interpretation of what that could mean in terms of parts????

Ozvtr wrote: ↑Sun Nov 22, 2020 11:10 am Hi Jmmj and welcome to the forum.

Wow! Potentially I could have a massive tirade on this subject but I will save you the nausea. That doesn't mean this wont be long!!

Ok, depending how you want to look at things your car is about 4th generation, if you take the Saxo and its peers as the first generation.
I don't live in the UK and am not familiar, first hand, with the models and evolution of the C3.
My area of, shall we call it 'expertise', is the second generation (2003-2005) but I am quite familiar with the 3rd generation (2005-2009). I am also fairly familiar with the versions of LEXIA associated with those years.However from the 4th generation on it's getting a bit grey.

First up the software and LEXIA3 (hardware) that you are using are pirated!!!!!!
The software is designed to run as a satellite from a server (over the internet). On that server is the documentation and other stuff that you might be looking for. This is why you get an error when you click on the documentation button. BUT, not being a Peugeot/Citroen dealer you are NOT entitled to access to that server. Even worse, Manufacturers are now beginning to take the attitude that you are not even entitled to view their Intellectual Property I.E. service documentation! So we are left with the likes of Haynes to provide documentation. Their days may be numbered! Governments are now falling in line behind big business and failing to protect those who make a living repairing others products. If you pay and are entitled to the information Citroen will part with some of the information. But this is on a subscription basis. No pay, no access.

There are basically two forms of software for Peugeot/Citroen cars, Peugeot Planet (for Peugeot) and lexia (for Citroen). The "front end" for both of these is Diagbox (as you know).
There are two more forms of software that Peugeot/Citroen uses called SEDRE and Service Box.
Combined, the two have, service manuals, service history/schedules (and other logistics), fault diagnosis and the parts breakdowns. However they are designed to run on a server, not on a stand alone PC. Yes, there are pirated versions of those (out there) but harder to find and difficult to install on a PC.

There is a small diagnostic area in the LEXIA program. When you are in LEXIA and reading the fault codes, there is box down the bottom with diamond shape in it. This diamond represents the diagnostics flow diagram and if you hit the Function key (F3 I think) nominated in that box, it will give you some basic steps to try.

You must remember, this is professional software designed for professional technicians who have been trained to use this software. So help is going to be minimal.

LEXIA is only a tool, just like a spanner or screw driver. It must be used in conjunction with the users skill and knowledge.

The ECU's (the control boxes) have limited resources at their disposal. Typically it can tell you what's happening but it cant tell you WHY. For example, in your case, the engine ECU and the gearbox ECU are not talking. It doesn't know why, just the fact that they are not talking. As I said, IF there are some diagnostic hints for the user there will be a button down the bottom. There is not always that button there and sometime the diagnostic may specify use of a specialist piece of equipment that you may not have.

You are right, some of the fault code descriptions are vague at best but the user is supposed to have access to facilities that you don't. In fact, it is possible for the Citroen technicians to hook your car up to a LEXIA which is networked and have technicians at head office France (or whatever) tell the technician working on your car what to do. What chance do you have?

Like the ECU's, you have to muddle by with what you've got.

I'm sorry but the theory of fault diagnosis would take up pages and pages. Try searching for general car fault finding tutorials. Forget about the LEXIA specifically. Remember the LEXIA is only a tool. Use it to gather clues.

I have worked with ATE (automated test equipment) and I rarely find it works. They are designed by engineers who don't have to fix the pieces of faulty equipment. Engineers and technicians are mortal enemies, LOL! So if you think LEXIA is going to tell you what's wrong...well...no, not most of the time.

If you have any more questions...fire away I will try to help.

C3CAR wrote: ↑Sun Nov 22, 2020 4:07 pm

1) Whats the 'work flow' for using the diagbox?? I

It all depends on what you want to achieve, from making changes to the configuration (e.g. adding keys) to diagnosing faults.


To fix faults:
Scan for errors from the main diagnostic screen,

Call up the fault and read it's description (in this case an intermittent faulty switch signal is reported)


lexia-diagnostics.png


From this you could use live data to monitor the signals that the ECU sees from the brake pedal and make a determination from the result of that.

You also have the option to press F5 (or click the button circled) to bring up the Citroen proposed solution (if there is one) and follow that too.

jmmj wrote: ↑Sat Nov 21, 2020 6:46 am Now the information offered in Diagbox is basically just the code with little or no indication of 'go change x part'...

It doesn't work like that. The ECU doesn't know what part is faulty, other than the data it is presented with over the bus in not what is expected. It is the job of the technician to work out what is causing the fault.

For example, from several codes i know i have a dodgy brake switch. I also have an error code D308:

"Communication error between the automatic gearbox and the engine management"

Why is there no interpretation of what that could mean in terms of parts????

Well, it does.

"Communication error between the automatic gearbox and the engine management"

is telling you parts are the communication bus and its connections and the data on that bus associated with the engine management and the auto gearbox. It takes diagnosis by a tech to understand what is causing it. F5 may give you a list of checks to do. But, for example, if this only occurred once, when the car battery went flat, it won't be worth pursuing. It is a different fault if it is permanent and stopping the auto from changing gear.

When I am presented with multiple faults, I would check/test and fix the easy ones first , particularly if they could be linked (like a blown fuse). Then scan again to see if fixing one has had an effect on any other.