Technical Ducato 3.0 keeps moving in neutral

[gdrmedic]

Hi,

We have a 3.0 Ducato Ambulance, with automatic transmission. It's been standing for approx. 12 months. New battery, got it going and through MOT today.

Having driven it a little it keeps beeping, and then moving to neutral. Code scan shows P0856. It also keeps throwing odd CAN errors. We did have an issue getting it ready when the wipers refused to switch off, but that seems to have resolved.

Can anyone help/advise? Moving through the gears well, auto and manual work well. Just periodically moves into neutral.

Thanks,.


Gareth

 

[Anthony489]

Hi

Some owners in the past have reported a problem where the wiring harness above the bonnet hinge around the offside headlight moves slightly, the chafing eventually allows it to occasionally short out against the wiper motor arm. This results in the comfortmatic gearbox disengaging, presumably as a safety measure as it has lost a vital signal.

The generic error code P0856 relates to traction control, but might also be to do with the engine control module losing communication with the gearbox so the cause could be the same as above.

 

[gdrmedic]

Hi

Some owners in the past have reported a problem where the wiring harness above the bonnet hinge around the offside headlight moves slightly, the chafing eventually allows it to occasionally short out against the wiper motor arm. This results in the comfortmatic gearbox disengaging, presumably as a safety measure as it has lost a vital signal.

The generic error code P0856 relates to traction control, but might also be to do with the engine control module losing communication with the gearbox so the cause could be the same as above.

Thanks, I'd spotted a couple of old posts about that, will take a look today. Hoping that's it, as not really useable at the moment.

 

[Anthony489]

Hi again

Another thing I should have mentioned is that vans that have been parked up for a long time are at risk of damp getting into electrical connectors.

When you pull off a connector and look at the pins/blades they should ideally all be shiny "silver". As corrosion progresses they will go dull "frosty" grey, then white or greeny white and finally black. If not too bad, a spray of specialist switch cleaner (not ordinary WD-40) and a few cycles of plugging and unplugging will often give a cure.

 

[gdrmedic]

Can't see any obvious damage to the loom, but this connector is just loose with no obvious female. Is it redundant or am I missing something

 

[Anthony489]

Hi

The wiring loom covers all options. If something isn't fitted in the factory they just let the spare connector dangle, so if there is nowhere obvious for it to go just ignore it.

 

[gdrmedic]

Ok, all wiring checked. Aside from internal breaks seems fine. Stationary seems to move through all positions fine, reverse, neutral, 1st and 2nd. Ran down the road, changes fine all the way to 6th. Then 'check transmission', and neutral. Error code now P0914. Live data seems 'ok', but don't know what normal tolerances are. Pump at 40 bar which seems correct?

 

[gdrmedic]

Looking into this in some more detail, could this be the gear position sensor?

 

[Anthony489]

Hi

The item you picture is a magnetically operated sensor which is part of the electro-hydraulic control unit on the outside of the gearbox. It measures the position of the hydraulic engagement piston.

I cannot find much information on the driver's gear selector knob, but that presumably has sensors or microswitches and a multi-pole connection to the gearbox control module. A bad connection or fault in this unit could also cause the control unit to "complain" if it loses the gear mode command signals.

Another thing to check is that the brake lights and their pedal switch are working OK, as if the system "thinks" you are braking whilst driving it will intervene.

I suggest you download Fiats "Teaching Guide M40 Robotised Gearbox" which is available here: https://www.fiatforum.com/downloads/teaching-guide-m40-robotised-gearbox.425/

Look at pages 14 and 44 for details of the piston sensor.

I also attach the users manual supplement.

I guess you have checked the hydraulic fluid level for the gearbox control ? (Separate Reservoir)

 

[gdrmedic]

Thanks, I'll have a read. I don't have an owners manual, but there is reference in a few posts about a gearbox reset procedure?

 

[gdrmedic]

Can anyone tell me specifically what P0914 means

 

[Anthony489]

Hi

I don't have a definitive list of Fiat codes, but P means powertrain, 0 means generic and 9 probably means transmission.

P0914 indicates a problem with the sensor that determines "Front/Back" movement, i.e. the shift from 1st to 2nd or 3rd to 4th etc
P0904 indicates a problem with the sensor that determines "Left/Right" movement, i.e. the shift across the gate

I imagine that with some setups, these two sensors are associated with the driver's gear selector. However, owners of the Alfa "Selespeed" models report these errors when one of the two sensors on the gearbox actuating mechanism is faulty. These report back to the ECU so that it knows the position that has been achieved by the actuator mechanism. Given the similarities between selespeed and comfortmatic, I would say that on balance we are dealing with the gearbox mounted sensors rather than the driver's gear selector. On the Ducato these two sensors seem to be of the same design.

 

[gdrmedic]

Hi

I don't have a definitive list of Fiat codes, but P means powertrain, 0 means generic and 9 probably means transmission.

P0914 indicates a problem with the sensor that determines "Front/Back" movement, i.e. the shift from 1st to 2nd or 3rd to 4th etc
P0904 indicates a problem with the sensor that determines "Left/Right" movement, i.e. the shift across the gate

I imagine that with some setups, these two sensors are associated with the driver's gear selector. However, owners of the Alfa "Selespeed" models report these errors when one of the two sensors on the gearbox actuating mechanism is faulty. These report back to the ECU so that it knows the position that has been achieved by the actuator mechanism. Given the similarities between selespeed and comfortmatic, I would say that on balance we are dealing with the gearbox mounted sensors rather than the driver's gear selector. On the Ducato these two sensors seem to be of the same design.

Yes, I think these are the sensors I identified above?

 

[Seanwinder22]

Yes, I think these are the sensors I identified above?

Hi mate I’m putting information together on all issues with comfortmatic and fix’s people did
Can you explain what you did to fix this please and I will make a note of it
It all helps others when looking