AL4 transmission in emergency mode

[CitroJim]

(Sorry about the off-topicness but the FCF has a minimum quote of thread de-railments to meet)

Oi! It's an admin's job to drag threads off-topic...

[addo]

Get on with it then, man. Do you rate Kate Williams, of Restoration Home?

[CitroJim]

Get on with it then, man.

I do my best

Do you rate Kate Williams, of Restoration Home?

Yes She's rather hot And a doctor too... Thinking man's totty...

This is the lady in question:

[addo]

We agree, it seems.

On the AL4 issue, mine has frequently logged temporary faults of a few sensors, making me wonder if it doesn't simply have enough buffering or whatever you may call it, to deal with glitches in signal continuity and identify the otherwise smooth flow of data - a bit like early CD players losing the plot.

[myglaren]

Get on with it then, man.

I do my best

Do you rate Kate Williams, of Restoration Home?

Yes She's rather hot And a doctor too... Thinking man's totty...

This is the lady in question:

A redhead too, an additional bonus

[Mr Micawber]

From hot redheads we go back to the mundane world of my C3. The story so far:

The wiring diagram shows that the CAN bus goes to the ABS ECU first then, via separate pins, continues to the AT ECU. So I'll see what I can find out from those clues.

I have checked the termination resistance of the CAN bus from BSI to ABS ECU and from ABS ECU to AT ECU. Both give the expected 120 ohms, and there is continuity between connectors. I have a couple of checks yet to do, but at the moment it's looking as if the loss of communication on the CAN bus is down to the BSI (already under suspicion for the "clicking relay" fault).

Hope I'm not boring too many people!

Simon.

[CitroJim]

Hope I'm not boring too many people!

Not at all Simon Especially when this thread contains a very attractive redhead

No, on the contrary, I'm finding this all rather interesting

[danielsydney]

I'm following your C3 woes as I have a automatic C3. Weird how they used such high tech electronics but the 1.4 engine is from the AX from what I have read. ....

[Mr Micawber]

... the 1.4 engine is from the AX from what I have read. ...

Greetings Daniel,

That probably explains why when everything electrical is crumbling around me, the engine keeps going! Old engine designs are good news.

But I have made an embarrassing discovery with the 'emergency mode' problem. Fuse 1 in the underbonnet fusebox supplies an 'ignition on' feed to the automatic transmission ECU. My owner's handbook mentions only the SensoDrive gearbox (naughty Citroen) so I didn't check this fuse. It had blown. Ooops!

I'm not claiming success though until I've reconnected everything and taken it on a test drive.

Simon.

[Chris570]

that is rather amusing if that solves it but i'd rather a red face and a blown fuse than a huge bill

[Mr Micawber]

Well, it hasn't cured it! But it has helped.

The fuse only blows when I select reverse.
When I disconnected the 12 pin plug to the transmission selector switch (on top of gearbox) I could select reverse without the fuse blowing.

The transmission selector switch contains a PCB with three switches:
1. Effectively a 3 pole 4 way device which tells the ECU the position of the transmission lever.
2. Effectively a single pole 4 way starter relay inhibitor switch.
3. A conventional microswitch in the reversing lights trigger circuit to the BSI.

Now I have to decide whether this switch has a fault which could result in 10 amps being drawn through fuse 1 when reverse is selected.

I'm particularly interested in which connection pattern I should expect to see from the 3 pole 4 way part of the switch. Does anyone have knowledge/experience of this?

Simon.

[xantia_v6]

The equivalent switch on my Xantia V6 (4HP20 transmission) had a similar fault and would intermittently blow the injection/transmission fuse, sometimes when moving the lever through reverse and sometimes without provocation. On the Xantia the fuse kills the engine as well as the transmission, so you really know when it has happened (usually at a busy intersection, once when performing a 3-point turn in a busy street and a couple of times when starting the car to leave the train on Eurotunnel).

I never did get around to opening up the old switch, but I presume that it would have developed a conductive path to ground due to copper/brass particles in the grease within the switch. You don't have a lot to lose by drilling out the rivets and cleaning it up inside.

[Mr Micawber]

The equivalent switch on my Xantia V6 ... had a similar fault and would intermittently blow the ... fuse ... I presume that it would have developed a conductive path to ground due to copper/brass particles in the grease within the switch. You don't have a lot to lose by drilling out the rivets and cleaning it up inside.

Thanks for that. Fortunately my switch is screwed not rivited together so I have already dismantled, cleaned and re-greased it. The tracks were visibly worn on the starter inhibitor section, but that's working just fine.

One conundrum is that selecting reverse blows the fuse, yet with the fuse blown the transmission's emergency mode still provides a working reverse gear!

Simon.

[CitroJim]

One conundrum is that selecting reverse blows the fuse, yet with the fuse blown the transmission's emergency mode still provides a working reverse gear!.

This is how it's supposed to be Simon, in emergency mode two gears are available purely by hydraulic means with no electrical help: 3rd and reverse.

As the fuse only blows when reverse is selected have you checked the light clusters and the reversing light bulbs themselves for shorts? Does the fuse still pop if the reverse light bulbs are removed?

[Mr Micawber]

Err... I found the fault today (and it's very embarrassing). I'd been busy with my multimeter tracing another fault; the random switching of the VAN +ve supply on and off. I hadn't noticed that a probe I was using to make connections to the multipin plugs had become stuck in one of them; in fact between the input from the reversing light switch and an earth pin! So every time the reversing light switch operated, the supply was promptly shorted to earth and the fuse blew. As this fuse also feeds the AT ECU the gearbox stopped working as well. Ah hem.

So you were right Jim, the reversing light circuit was the key to success. Thanks for your encouragement to look there.

Simon.