Technical Inertia Safety Switch

[sb20]

Hi, I've a 2009 Ducato and the inertia (impact) safety switch, which is supposed to cut power to the fuel pump in the event of a crash, doesnt do a thing. I can give it a good tap and I can hear it click, but nothing happens, no hazards, engine continues to run. Also if I disconnect the whole switch, still nothing happens. Any ideas please? A previous owner has had a vanbitz strikeback alarm fitted which I wonder whether has bypassed it. Thanks in advance.

 

[The Panda Nut]

My very limited experience of such things is that they take a hell of a knock to make them switch. They are not designed to be tested by knocking them.

 

[sb20]

My very limited experience of such things is that they take a hell of a knock to make them switch. They are not designed to be tested by knocking them.

Thanks PandaNut. Looking at the circuit diagram, I'd expect disconnecting it completely to have the same affect. I also heard that these can offen be sensitive with pot holes setting the off. There is certainly a distinctive click if I hit it hard enough, not enough to damage it though.

 

[The Panda Nut]

I guess, that the switch in normal state would be a closed circuit with continuity, if its been set off ot would be open and no resitance? Maybe someone else can add much more to the discussion??

 

[Communicator]

The primary purpose of the inertia switch is stop the electric fuel lift pump feeding fuel into any post collision fire, or providing fuel to start such a fire. The switch has been known to prevent starting, but may not stop a running engine, as the hp fuel pump may be able to develope sufficient suction to pull fuel from the tank.

It is worth noting that at least some pre 2000 Ducato engines, all of which had mechanical injection pumps, did not have a separate lift pump, and relied on the transfer pump incorporated in the injection pump to draw fuel from the tank.

I would think carefully before cutting the power to the lift pump, as the hp pump relies on the fuel to provide lubrication.

 

[deejays]

Hi, I've a 2009 Ducato and the inertia (impact) safety switch, which is supposed to cut power to the fuel pump in the event of a crash, doesnt do a thing. I can give it a good tap and I can hear it click, but nothing happens, no hazards, engine continues to run. Also if I disconnect the whole switch, still nothing happens. Any ideas please? A previous owner has had a vanbitz strikeback alarm fitted which I wonder whether has bypassed it. Thanks in advance.

The Sensata inertia fuel cut-off switch in my 2018 Ducato is a simple single pole double throw switch. The centre toggle contact of the switch is wired to earth and normally supplies the tank pump with earth. When inertia switched, it toggles and removes the earth from the pump to the other contact which triggers the dash alarm and hazards. I suggest someone has wired the alarm incorrectly and by doing so has disabled the normal operation of that switch instead of having it also electrically triggered by the alarm.

 

[Communicator]

The Sensata inertia fuel cut-off switch in my 2018 Ducato is a simple single pole double throw switch. The centre toggle contact of the switch is wired to earth and normally supplies the tank pump with earth. When inertia switched, it toggles and removes the earth from the pump to the other contact which triggers the dash alarm and hazards. I suggest someone has wired the alarm incorrectly and by doing so has disabled the normal operation of that switch instead of having it also electrically triggered by the alarm.

eLearn for the x244 shows the normally open contact of the inertia switch being used in the additional heater (Webasto) control. I do not have this optional feature on my x244, however on checking further the contact is used to operate a normally closed relay, which interrupts the supply to the Webasto fuel pump motor.

I have been involved in a thread on this forum, relating to starting or was it running, problems on a 2,8jtd?. A photo was submitted which revealed the inertia switch hanging loose in the wiring, but it may previously have been pushed behind the battery. The OP on that thread did not appreciate that the switch should be mounted vertically. As I recall tet problem was traced to defective non OEM connections at the battery negative terminal.

 

[MSjoberg]

eLearn description for the inertia switch in X250 Euro 5:

The fuel pump relay T10 of junction unit B001 provides a direct battery power supply to the fuel pump N040 - pin 1 - along the line protected by fuse F21 of the engine compartment junction unit B001 (pin 16 of connector A).

The coil is energised by pin 94 of connector B of the engine management control unit M010; the coil for relay switch T10 receives a reference earth, via pin 11 of connector C of the engine compartment junction unit B001, coming from the NC contact for the inertia switch I050 (pin 3).

In the case of an impact the inertia switch opens, no longer supplying the reference earth to the coil for relay switch T10 and thereby interrupting the activation of the fuel pump N040 and the additional heating pump N044.

 

[Dave Ducato]

I hit a pothole about a year back and the pesky inertia switch turned the engine off and put the hazard lights on. I had no idea at the time what had occurred. Thank goodness I had a good phone signal and found the issue through Google, then a guy on Youtube showed where the switch is located, this saved the day.