Technical Punto MK1 not preheating

[wannesd]

Hi everybody,

I'm new to this forum, and I've got an (sort of) emergency.

I drive a fiat Uno, which works great (for now).

However, my neighbor and good friend, drives a fiat punto van, mk1. Not sure what year it's built though. This morning, the glow plug light didn't light up, and his car would turn over but not start. I checked all the fuses, but none were blown. Checked for 12V at his glow plugs with ign in glow position, but sure enough, no voltage was supplied.

So I'm guessing either a blown relay, broken wiring, or maybe a hidden fuse?

I'm used to working on my jeep and my jaguar, but for them I have full service manuals and electrical diagrams, making it easier...

any ideas?
Thanks!

 

[red]

Hi,

Welcome to the forum wannesd.

There is a glow plug control unit somewhere. It has the following connections:

* Batt (+), unfused.
* Pin 1 - Black/violet - earth.
* Pin 2- Blue/white - to coolant temperature sensor (other side of sensor is earthed).
* Pin 3 - Orange - supply from ignition via injection system relay (coil of relay on with ignition but its earth connection can be cut off by inertia switch - find and check that (maybe it's near passenger door like the petrol version).
* Pin 4 - Red - Supply from ignition when starting.
* Pin 5 - Blue/red - to warning lamp (other side of lamp is earthed).
* Supply to glow plugs.

red

 

[wannesd]

Hi,

thank you for the reply, it's very useful info!

So far, here's what I've found:

The module does not switch the constant 12V to the preheaters.
Now, is the module broken, or is there a sensor acting up?

From what you told me, only the coolant temp sensor has a saying in this, but when I measure from the module connector pin 2 to the ground, I get infinite resistance. Maybe a broken wiring, or is this supposed to be like this when engine and ign are off? (note that at this point, in order to measure, connector is not attached to module).

Will hunt down the temp sensor, and check for continuity of the wire from sensor to module.

Since this is my friends car, I'd hate to make him buy a new preheater module if it turns out to be a broken wire.

Will return with my findings

 

[wannesd]

I seem to have found 3 coolant temp sensors

Neither gets a solid connection to the pin 2 on the module connector.
Neither has the blue/white wire.

Do you know to which one the blue/white wire connects, and whether it changes color?

Maybe I can fix all this by just fixing some stupid broken wire, would be cheap

 

[wannesd]

nevermind,

found the temp sensor I needed, rear of the engine.
All wires check out ok, everything behaves as normal (except maybe the sensor itself, don't have any "normal" values for that, so can't check it).

I'm thinking a busted module...

oh well, that's another 75 euros well spent

 

[red]

Not familiar with these diesel engines but temperature sensors are generally based on negative temperature coefficient thermistors. This means that resistance goes down as the temperature goes up. I suppose the function with glowplugs is to shorten or eliminate the pre-heat when the engine is hot. If the sensor is reading infinity, it is probably suspect (as I said, not familiar so it's your call). Perhaps the local scrappy can meet your needs?

red.

 

[wannesd]

yeah, forgot to add

that whole infinity thingy was my multimeter, one of the plugs was not seated correctly

got a steady resistance after double checking, so I'm gonna assume the sensor is still doing fine...

Thanks for the help anyways, I can go pick up the new module tomorrow, hopefully I'll be able to tell you all that sorted it out!

PS: working on electrics without a decent wiring diagram is a pain in the butt!
For my jaguar alone, I've got well over 300 pages, very detailed. My jeep is a close second with 220 pages, and that's a 1989 vehicle! But all I could find for the punto mk1 is an incomplete haynes manual, lacking the diagrams

 

[wannesd]

Alrighty, that solved the problem!