Thanks 86cj74.2L ....... Have been struggling to find a 'break' etc.... If its a common earth issue (to those sensors) could hurt to take a new earth from one of the 'paroblem' sensors straight back to battery /thus giving a good common earth??? Is that logic sound????
I would trace out the 5v supply to all the sensors or look for the sensor ground.
It may be a bad sensor ground.
It may be the harness is lying on something that gets hot and has melted the wires and shorts out on occasion.
A volt meter on the 5v supply to a sensor effected at the time the MIL comes on will tell you next step.
Check 5v to the engine somewhere and also check the 5v to the sensor common pin on the connector.
Okay, have just had a brief play.... and am a bit confused!
One of the 'faults' is for the MAF sensor and another for the Turbo sensor.....
4 wires to the MAF connector....brown is ground. Getting a 14v reading when running at MAF sensor. Tried Turbo sensor.... brown ground here also...... Getting 14v here also..... Should this be part of the 5v system /running 5v? It is a merc unit so poss different to the petrol ones????
Anyhoo, ran in a new ground to the MAF ground and back to battery and also body....neither cleared fault.....
Without a FSM for diesel model I can't rightly say it should or shouldn't be 5 volts.
When you read the 14v on the brown wire.......tell us where your meter leads were placed.
There should be a supply and ground in each connector.
With ignition on and connector pulled you could read across those two pins and see what you got for volts.
Thanks for your continued help! Tried as you describe (pulled connector) and for MAF get (ground brown wire, supply green and red stripe) 12.5ish not running and 14+ish running..... Ditto turbo sensor.
Originally Posted by alfaitalia
My sensors run 12.5ish volts when engine off and 14 ish engine running so I would suggest this is normal at least for those two sensors. Others such as the fuel rail pressure sensor def run at 5 v.
Thanks Alfaitalia Same as mine..... Guess I'll keep working through the sensors showing on the fault list
Keep the suggestions coming all....really appreciated!
May be it would be better to back probe the connector with it still connected. That way your seeing what the PCM is seeing.
Some MAF sensors are 4 wire and include a inlet air temp.
CRD's do have a 4 wire sensor. But they also have an air intake temp sensor on the bottom of the alloy intake manifold on the other side of the motor. I got so fed up cleaning the oily crap off it (it gets contaminated by the oil in the PCV and makes the car hesitant just off idle and at very high revs) that I vented the PCV to the atmosphere......have not cleaned it since!
If you can't fix it with a hammer, you've got yourself an electrical problem!