C4 EGS Gear Selector Coherence Fault

[AlienC4]

Hey Guys,
My first post - It's an intermittent problem that seems to be getting worse.
When working normally, it drives fine but sometimes a 'faulty gearbox' message flashes up..
when this happens it will still drive normally until you need to select 'N' or 'R' and then you're stuck in them until the car decides otherwise.
I used a 'Launch' diags to get the selector coherence fault but it didn't come up with a code.
I've messaged a couple of the Lexia owners on your map and awaiting replies.

I tried the "detach battery for an hour thing" and noticed that one thin lead, on the loom that sits on the battery, is detached and going no-where.
This is a thin light blue lead with a small pin-socket on the end - don't know what the heck this is for.
I have a photo but unsure how to post it.
Any help would be REALLY appreciated.
Thanks Jon

[myglaren]

It can sometimes take a while before receiving a reply as not all members log in regularly.

You can email the photo to me - myglaren at btinternet dot com (my email link on the left appears not to be working).

Otherwise there is a photo-posting guide here.

[myglaren]

Image added to original post

[AlienC4]

Just had a new diags result from a 'snap-on'. The gear selector coherence fault is coming up with a P1704 error code.
Does anyone have any experience with this?
Thanks

[GiveMeABreak]

That code is: P1704 Brake switch signal : Consistency between 2 brake signals. I don't have one of these systems, so can't comment further - but would be tempted to look at the brake switch as a possibility? There are a few C4 owners who may have more info if you hang on for a bit.

[RichardW]

The brake light switch is a well known fault - pretty easy to change (passenger foot well) and the new one (about £30 IIRC) comes with a modified loom section.

[AlienC4]

Thanks guys but how can a gear selector coherence fault be related to the brake switch?

I read that it's related to "digital TRS failed to transmit states in KOEO/KOER

[GiveMeABreak]

You would be surprised at how many components talk to each other on the networks - speed regulation (cruise), speed limiter, EPB, ABS, ESP etc., for information to determine whether something should be applied or not - I've spent a lot of time buried in wiring diagrams and it is quite interesting on what data is sent through the the various ECUs before determining a course of action!

[AlienC4]

Yeah I see what you're saying...

Since my last post, I think I actually got to the bottom of my problem.
I don't want to speak too soon but it looks like it was all down to that blue wire "on the top of the battery" matrix pictured a few posts above.
It seems that this got pulled when reseating the plastic battery cover a few times as there are a few bits that can 'catch' the wires.
I looked into it and found where the wire should go as arrowed.
Bobs yer uncle, all errors cleared, starting ok, selecting all gears ok, Sainsbury and back.... ok !
After a month of just sitting there outside !
Still I'm glad it was a simple solution.

I'll give you a quick run-down of what was happening with this wire detached for info:
Came up with "gearbox fault" and that error code 1704.
Had trouble selecting between 'R', 'N', 'A1', 'M'.
When trying to start even in 'N' and foot on brake to start - it would often STILL give the select 'N' and put foot on brake message - so wouldn't start.
When it did start by chance, it would come up with errors and would be very erratic in gear selection and would skip between manual and auto, only going up to gear 3.

So before going onto any other diags, just check this wire is fully home and connected if you have a similar set-up.

[GiveMeABreak]

Nicely done, and good to get the update

[AlienC4]

Thanks Marc,

Hey it was looking so good yesterday all faults disappeared and today.... Bloody 'gearbox faulty' message comes up again.
So not quite back to square one but there's still something wrong.. Today I took the advice of other posts and tried to clean the gearbox ecu connectors after spending hours trying to figure out how to get the things off.. it seems like every connector has a different 'key' to getting them off just for a laugh.

Wasn't sure what to do to 'clean them' so wiped off the grease and used some contact cleaner on them - is that good or bad ?

Still same message come up after a while and doesn't want to switch between R, N, A1. Once in 'R' it wants to stay there !
I'm gonna throw this c4 in the bin before long Lol...

[RichardW]

You need to get it on a Lexia to see what is going on. Anyone near you: http://www.frenchcarforum.co.uk/forum/v ... 19&t=29178 ?

[GiveMeABreak]

I think Jon mentioned he is awaiting some replies from Lexia owners Richard, buit I agree - there are varying issues with these EGS systems and seeing that the issue has come back again, it really could do with diagnosing.
Odd behaviour can result from either the Gearbox or Clutch actuators - listed by Sinspeed who refurbish these as:
Won’t Rev in Reverse
Gears Won’t Select
Selecting Wrong Gears
Going in & out of Auto Mode
Showing ” – ” Sign Instead of Gears
Showing Snowflake Sign on Dash
ECU Logging Clutch Actuator Faults
ECU Logging Gear Actuator Faults

Hopefully you'll get a response soon Jon.

[AlienC4]

Thanks Marc & Richard , although these sinspeed guys have some terrible reviews :/

Still here's a thing... the car works perfectly normally until that 'gearbox faulty' message comes up..
when this is up, it will still drive normally if you happen to be driving and in 'A' - fine through all 6 gears.
It's only when you want to change the selector there's a problem.
If you go into reverse, that's it, you're stuck there until the car feels like letting it go..
Like today, just outside my house, it came up with the gearbox fault and stayed in 'R' so I just switched off, left the selector in 'N'
When I went back an hour later turned on the ignition, on the display the 'R' quickly changed to 'N'
and it's back to normal for a while, selecting all gears as normal again..
Bloody thing

BTW when I had the 2 x gearbox ecu connectors disconnected, the display changed to - 'parking brake fault' with 2 dashes.

[GiveMeABreak]

Thanks Marc & Richard , although these sinspeed guys have some terrible reviews.

Agree - they don't inspire confidence - it was just the causes that were similar - there's a few other places listing similar issues - but I wouldn't recommend unless I had used them myself Jon.
Hopefully you'll get a response soon.