Technical P1773(7B) DTC - Comformatic Gearbox Pump Motor Fuse blowing

[arob]

G'day All,

I am having issues with a 2019 Ducato 250 6 Speed Auto with the Comformatic gearbox. The Van will not go into gear with warning 'gear not available' on the dash. I've plugged ab OBD2 scan tool in and got the DTC code P1773(7B) Low Hyd circuit px. I noticed when i opened the driver's door i couldn't hear the gearbox motor/pump.

I checked and found the Gearbox pump 30AMP fuse had blown (located in an auxiliary fuse box next to the main fuse box under the hood). I had to order replacement fuses from Fiat. I replaced the fuse and tried again. On opening the driver's door i heard the motor/pump kick into action for about 2-3 seconds and then Bang...fuse blown again...

Has anyone got any idea whats causing this and what needs replacing. I'm hoping maybe its maybe just the motor as i believe this can be swapped fairly easily although i've not looked into it too much yet. Could it also be the pump and would it be worth replacing the whole pump unit (pump/accumulator/motor) as opposed to just the motor?

If anyone has any experience or advise on this issue it would be highly appreciated, Thanks in advance.

 

[MSjoberg]

Yes, that fuse is of a rather uncommon type, Maxi Compact. It might be possible to source from other suppliers than Fiat in Aus also.

I´m not sure if a "blocked" pump would cause the fuse to blow that fast, my first guess is that there is an electrical fault in the pump motor, wiring, or relay. But I may be wrong. The pump should be accessible from below I think. I would try to unplug and check for faults in the wiring before removing the motor.

(There is a Comfortmatic spare parts list available in the Downloads section.)

 

[arob]

Hey mate thanks for your reply. So I’ve ordered a new pump motor and relay from fiat $600, the pump assembly itself is $11k so let’s hope it’s not that. I agree with you about the wiring, I’m not great with electrical testing but will try and locate the wiring loom and have a good look at overall condition. I’ve spoken with a mechanic who said you have to drop the gearbox to be able to replace the motor, I’m really hoping that’s not the case as I don’t have the tooling. Hopefully I can get access to the pump motor by jacking vehicle and coming up underneath or removing adjacent tubes and parts in the engine bay as it does look buried in there.

 

[MSjoberg]

Below is a Google translated text from a German forum. It doesn’t seem to be neccessary to drop the gearbox (but maybe quicker?) This guy obviosly made it lying on the floor under the car. I suppose a mechanic with a lift can do it significantly faster:

” Repair of pressure supply unit Approx. 7 hours of work without a lifting platform in an inhumane position. Pressure accumulator and pump motor replaced. Pressure accumulator alone would have been done in < 1 hour, but to be on the safe side I also wanted to replace the pump motor. The latter requires the complete removal of the supply unit, while the pressure accumulator can be replaced relatively easily without removal.”

 

[arob]

Ok thanks for the info! I did read on an another forum of someone who replaced the motor alone by removing the air filter box/housing and turbo pipework and managed to gain enough access. That may have been on an older/newer model. I don’t know why the whole supply unit would have to come off to replace the motor, it looks like it’s bolted on to the supply unit with 3 screws from the pictures of the new one. Guess it will be a suck it and see job, luckily time isn’t an issue. Thanks again for your advice will update how it goes.