Snowflake; Auto Gearbox Reset

No reverse? - see also  clutch reset 

Problem is often that when you change gear, three heavy duty motors operate for a fraction of a second.  This drops the battery voltage momentarily and upsets the engine ECU - and maybe then the gear change misses the very small time window.  So everything has to be perfect -  especially the battery. 

If the problem continues then you may need to disconnect every plug and socket in the clutch and gear actuator circuits as the contacts can corrode inside.

Auto gearbox:  In hot weather, occasionally something can overheat.  Several have found that it helps to select N (neutral) if kept at a standstill in heavy traffic.

These autos are fine - except that very occasionally in hot weather and heavy traffic with a lot of stop/start driving they will bring up a snowflake.  The "cure" then is to wait up to 15 minutes and all will be well.

The paliative is to flick the gear into neutral at any long stop (like traffic lights) and the problem seems to go away.

Cause is possibly the gearbox ECU overheating (mounted on the side of the gearbox) under exceptional circumstances.  With many thousands of these gearboxes on other Citroen and Peugeot cars, it is not unreasonable for one or two to give problems in abnormal conditions.  Mine has never given any problem.

Possible cure for overheating gearbox ECU

After removing the air silencer box and pipe to the air filter, Vivian Carelse has taken the ECU off the gearbox and moved it up to between the radiator and battery box.

Wires are long enough without disconnecting it. It now needs a bracket to mount it on the battery box.

Chris Holmes managed to squeeze his gearbox ECU into this tiny space without removing anything.

Wires are long enough without disconnecting it.

Another possible problem might be corrosion inside the in-line fuse-holder.

This in-line fuse is hidden under the air filter box and/or battery box. The fuse is unlikely to blow, BUT any corrosion could affect the supply to the gearbox ECU, as Chris Holmes discovered.

The small black fuse box is on the end of a piece of cable conduit and can be manipulated to become more visible. There is a 30amp fuse and the contacts on his were corroded. Chris cleaned it, and the socket on the fuse box, and rerouted it so it sits by the rear left of the battery box.

Just think that 30amps flowing through just 0.1Ω contact resistance will instantaneously drop 3volts so depriving the gear actuator of the full voltage it needs to operate quickly.

This alternative fuse for the ECU is mounted, on its own, on top of the gearbox.  Access after removing the air filter box.  This (possible replacement) appears to be secured in place.

"Automatic Gearbox Fault" indication - "auto" and "snowflake" flashing.

This can happen as a protective precaution if something overheats, eg in hot countries or in heavy traffic.

Before panicking, try to reset the 2-tronic gearbox electronics:

BEFORE you disconnect the battery you must let the systems go into stand-by or you will create more 'errors'.  And after you reconnect the battery you need to allow the systems to initialize before opening the doors or doing anything further.

  1. Ensure the windows are up ensure everything is off (e.g.  radio) make sure the key is out of the ignition and close all the doors and boot (do not lock the car).  However for peace of mind, I always leave the windows open so I can get to the ignition switch and bonnet release as the deadlocking is very effective!
  2. Prop the bonnet up and remove the front battery cover.
  3. WAIT A MINIMUM OF 60 SECONDS and then remove the + battery terminal.  Leave it off for at least 5 minutes (or have a drink to settle the nerves).  Then reconnect it.
  4. WAIT A MINIMUM OF 5 MINUTES after reconnecting the +ve terminal to allow the electronics to settle before opening the doors.
  5. Now check the gear selector readout on the instrument display.  It should have a "-" sign as the gear selected.  If it doesn't, disconnect the battery for a longer time.
  6. If you do have a "-" sign, put your foot on the brake and turn the ignition to "on" (NOT start).  The gearbox should hum and click and clack for a short while, keep your foot on the brake during this time.  At the end of this cycle the gear selector on the dash should show "N" or a number.  If the gearbox doesn't make any noise and a "N" or a number appears straight away, remove the battery terminal as above and try again.
  7. If not faulty, the gearbox should now be OK - remember to reset the time clock on the multi-function display.

I accidentally simulated this snowflake situation one day after leaving the engine ticking over on the drive for a protracted period.  I believe that the gearbox ECU is being heated by the gearbox - and the gearbox ECU senses overheating and trips out which suggests that the problem may be lack of airflow.

If the answer is airflow then if you have an undertray, take it off.  But mine has an undertray and I have never had the snowflake out on the road so maybe adding an undertray has ducted the airflow - who knows?

In addition to flicking it into neutral at every prolonged stop, put the air conditioning ON.  This should make the radiator fan come on at full speed and help blow air past the ECU when the car is stationary.

As far as I know, no-one has tried mounting the gearbox ECU in a cooler area.

When it happened to me, after three attempts I still had the snowflake and auto symbols flashing - though I could now engage 1st and reverse.  These indications cleared after driving the car a very short distance (25 yards).  For some reason this worked for me; possibly because the alternator cut in and raised the battery to 14.3 volts

Note: you may also find that the power asssisted steering has not enabled, which may take you by surprise first time.  It comes back after a while, as do the other gears.  It appears that there is a step by step recovery of normal running as each part of the system reports back to the BSI and it adjusts to the new system state.

No reverse? - see also  clutch reset 

Neil Gibson reminds us that what you might think as a transmission problem could be a symptom and not the cause.

Each electronic control unit feeds data via the BSI unit or body control module to the gearbox.  A momentary glitch can have interesting results.

A recent problem with an ABS pump resulted in the sliding doors failing to open.  Why should the ABS impact on the doors? The door control module won't allow operation above 3 mph.  No speed reading.  No door opening.  The doors get blamed again!

The gearbox is the same.  Virtually every power train sensor from throttle position to wheel speed can affect gear selection

Arnie Fouche suggests (if auto won't select or engine start):

Google: "How to repair clutch actuator on Citroen C3"; look for the 4th video Pete's Workshop
and then
Google: "Citroen C2 EP 6 Sensodrive calibration" - this is a long video!
It turned out to be a battery problem - eventually proved on Take 11 at around 14 minutes!