No voltage at some sensors

[JVB88]

Hey guys,

I've been struggling with multiple problems with my 2000 306 1.4 petrol. I'm an amateur mechanic, and wiring is certainly not my specialty. Problems ranged from a faulty wiper motor, faulty ventilation motor, radiator fans turning off and on irregularly... Also, problems with running while cold (stalling!), irregular idle especially cold, but also moving between like 600-1400 when it returns to idle... I'm starting to think it's to much issues to easily solve, but I still like the  car and it still looks pretty good for its age...

Now, after acquiring a multimeter to test some sensors, I found out the sensors itself seem fine, but voltage to different sensors is zero/low? Including green and brown coolant temp sensors, which could explain cold start and fan issues? Also idle control valve(is that the right term??), map sensor.. Haven't tested every sensor, but others do have stable 5v, the blue temp sensor, tps.. Could there be a common point in the harness broken or something? Ground issue somewhere? Something I'm missing?? I did check grounds just below the battery but don't no where to find the rest? 

Any tips.....?

[Mighty306]

Welcome to the club. Well, you've made a good start by identifying you have a low reference voltage for your sensors. My next steps would be to remove, clean & secure the grounds that the ECU use. I think they're the ones near the fuse box (drivers side wing on a left hand drive car?). Then inspect the wiring coming from all of the affected sensors, all the way back to the ECU. It's possible one of them has rubbed through somewhere & the 5v reference is being pulled to ground. You may need to remove the battery & battery tray & possibly unwrap the harness to make a proper inspection. I'm not sure how much space there is in that part of the engine compartment on a 1.4. (On a 2.0 there isn't much!).

[JVB88]

Thanks for the tips! According to the Haynes manual, the ecu sensors use ground point E3 - 'back of engine block'. The other 2 near the battery box are in the same circuits... Gonna try the 2, but the third? Do you know where exactly? And how to reach it haha? From under the car??

I already found out my brown temp sensor is faulty because of a cable break directly above the sensor, as I can make the fans turn on by just wiggling the cable.. What are the sensors Peugeot uses named? Are there like repair kits for sale somewhere? 

And also, how is it even possible the car runs reasonably fine with so many sensors not getting voltage??

[Mighty306]

Sounds like the brown sensor is fine but you'll somehow need to fix the wiring to the plug. Not easy if it's very close to the plug & as far as I'm aware those specific plugs aren't aware as a replacement. There are work-arounds.

As far as I know all the petrol models had another 2 coolant temp sensors - a green one which sends info to the ECU (adjusts fuel mix according to engine temp), and the blue one, which feeds the temp gauge in the instrument cluster.

Assuming you were asking, the other sensors your engine will have are:

> Crank position sensor - can wouldn't start without this functioning so must be providing sufficient signal
> MAP - senses the air pressure in the manifold to help calculate how much air the engine is drawing in
> Knock sensor - detects 'pinking' due to pre-ignition
> Air intake temp sensor
> Throttle position sensor
> O2 (lambda) sensor - in exhaust

The ones the engine really relies on are the green coolant temp sensor, throttle position, MAP & O2 sensors. If any of these were significantly out it would run fairly badly, but likely it would run.