Non starting 306

[Adriansparkes]

Need so help as where to start looking:
was out yesterday in 306 cabriolet (1.8 16V, 2002 registered), was fine all day until i went to shops, parked up ok, went back to car and would not start (it tried to fire up once but died straight away), battery fully charged and spinning engine over but just would not fire up. (It has a new fuel pump fitted last month to fix gauge not working so I doubt its the fuel pump)
I have done some preliminary checks and I’m only getting 3volts on the fuel pump circuit, I’m getting 12v to plug 11 on engine management relay but only 3v on output side (plug 9). Need to check plug 10 (from ecu) but it’s looking like an electrical problem
Just wondering if it’s Immobilier connected preventing the ecu from suppling fuel pump with 12v?

[wheeler]

The factory fitted immobiliser doesn't stop the supply to the fuel pump, it stops the injectors operating.
Does it start if you supply the fuel pump with 12v?
Cant really think of the exact setup on the 306 but on the Xsara (very similar to the 306) there were a couple of big round connectors behind the engine ECU that were bad for causing a high resistance on the fuel pump circuit dropping the current. worth a look.
Really need a wiring diagram to do further checks.

[Shredder11]

I had the same problem last June 2019, and I tested the fuel pump etc etc, swapped parts between my other identical 306 car and no joy. I then thought about the crank sensor and then after Googling, found that the inertia button switch under the bonnet behind the battery, can sometimes trip and shut off the fuel supply. If the switch has done this it will cllick when pressed again to reactivate it. Mine did click and the car started and run normally again after that.

One other issue I have noticed with this particular 306 of mine, is that if I corner hard, accelerate briskly or brake firmly, it brings on the flashing air bag dash warning light. This will go away upon turning the ignition off and on again. I wonder if that contributed to the interia switch cut off I had last year?

[white exec]

The inertia (crash detection, fuel cut-off) switches, fitted only to petrol engined cars now, are easily forgotten about. Not helped by, SFAIK, there being no dedicated dash warning if they trip out.

[wheeler]

Inertia switches are getting quite rare now with many manufacturers incorporating the function into the airbag systems, On early multiplexed PSA cars the hazzard warning lights would come on when you tried to start the car with a tripped inertia switch. The mk3 relay displays FPS on the dash when the inertia switch is tripped, stands for Fire Protection System.

[Shredder11]

My current running 306 2.0 XSi is a Phase / Mk2 model, so that explains the lack of dash warning I guess. My previous 306 2.0 XSi in the driveway is a Mk3 but I never had any issues like that, only the typical air bag light due to the wires under the drivers seat being worn etc.