Technical Glowplug control unit signal; earth, digital, analogue etc?

[kegless]

I have 2007 (x250) Ducato and the glow plugs dont work. They are not receiving power from the glow plug control unit, the unit however is receiving power but none comes out to the plugs, I replaced the unit but no change.

My question is what is the nature of the glowplug signal wire, is it a 12V/earth/analogue/digital signal? I suspect it may be a reference earth which my body computer is failing to produce for the low voltage side of the relay but before I put in a manual push-to-make (earth) override switch I want to check.

Similarly, I would be keen to know the nature of the timer/diagnostic wires and would this idea cause any problems.

Cheers, Paul

 

[CDK]

The ECU decides if and how long the plugs get power, based on the temperature info from the MAP sensor. In my van the plugs get no power unless the temperature is near or below freezing.
As a result, the engine starts quicker in cold weather.

Be careful with a manual override switch; the glow plugs are small and draw a high current that destroys the plugs if you push the switch longer than a few seconds.

 

[Anthony489]

Hi kegless.

I have had a quick look at my CD based service information, but it is unhelpfully not specific about the control signals. However, the Heater plug control unit M015 appears to be a glorified high-current relay, and normal practice for Fiat with similar setups seems to be to supply the coil with +12 volts and to earth the other end when needed by means (presumably) of a semiconductor switch within the associated control unit. In this case it is the Engine management ECU, not the Body Computer. The connection between the two is from Pin 93 of Connector B on M010, the engine management ECU, via a Brown and Red wire to Pin 10 of M015. Whether this signal is timed for the glowplug duration, or just initiates a timer housed within M015 I don't know.

As you have spotted, there is also a signal connection going back from M015 to M010 described as Preheat time/Fault feedback. Again I am guessing here but I think it unlikely that this is an analog signal, its more likely that it is +12v or 0v to indicate a fault or to tell the ECU that the plugs are being energised. I don't know which way round the +12v/0v signal sense is, but you could measure it with a DVM.

The +12V light current comes via T09 (main injection relay) via Fuse F11 (15 Amp) which are both in B001, the front engine compartment junction unit. The connection passes through Pin 7 of Connector C, then via a blue wire to Pin 6 of M015.

The +12V for heavy current for the glow plugs comes from Fuse F02 (50 Amp) in B001. The connection passes through Connector B, then via a thick red wire to Pin 11 of M015.

The ground connection for M015 is via a black wire to C010, the left front earth.

Once you have eliminated bad connections in any of the above as the cause and are satisfied that the fault is definitely in the engine management unit, it would be worthwhile isolating the M015 control wire and trying an external push to make switch as you describe. I suggest you use a low rated fuse such as 1 Amp in series with this as a precaution. The glowplug dashboard warning light may well be driven indirectly from the feedback signal, so best to leave this in place.

Cheers Anthony489