engine check light

hi. my missus was driving the 300 at 75mph when the engine check light came on and she experienced a part loss of power, she describes it like driving into a strong head wind, temp guage was normal. After easing off it went away and hasnt done it since, what i need to know is which sensors can trigger this light, im guessing fuel pressure, oil pressure. are these right and are there any more. i guessing/hoping it could be a choking fuel filter as she constantly drives it low of fuel but today it was half full. and help most aprecieated

benj said:

hi. my missus was driving the 300 at 75mph when the engine check light came on and she experienced a part loss of power, she describes it like driving into a strong head wind, temp guage was normal. After easing off it went away and hasnt done it since, what i need to know is which sensors can trigger this light, im guessing fuel pressure, oil pressure. are these right and are there any more. i guessing/hoping it could be a choking fuel filter as she constantly drives it low of fuel but today it was half full. and help most aprecieated

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You don't say if the vehicle is an auto or manual and what year, this would be useful info for the diagnosis procedure.

Presuming its a 300 tdi EDC Auto? Not sure if the earlier ones had a "check engine light" as they had no ECU?

The EDC takes input from -
MAF (and the thermister inside MAF for intake temp.)
Throttle potentiometer
Boost pressure sensor
Injector 4 Needle lift sensor
Crank sensor
Vehicle speed sensor (VSS)

So if any of these have gone out of tolerance then you'll be getting the check engine light up - much like what I'm suffering with at the moment on my 96 300tdi EDC Auto. However my light disappears when you release the accelerator and reappears if you keep the accelerator held down for more than 14 seconds, whereas I presume yours is on all the time?

sorry it is a 300 tdi auto n reg. im guessing it has a throttle sensor as i cant see a wire to the injection pump, tho i cant find it. im hoping its a one off as she does drive it hard but does the Injector 4 Needle lift sensor measure diesel pressure hense me thinking the filter is blocked or am i peeing up the wrong tree. thanks

benj said:

sorry it is a 300 tdi auto n reg. im guessing it has a throttle sensor as i cant see a wire to the injection pump, tho i cant find it. im hoping its a one off as she does drive it hard but does the Injector 4 Needle lift sensor measure diesel pressure hense me thinking the filter is blocked or am i peeing up the wrong tree. thanks

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Hey

As far as I'm aware it doesn't measure pressure, its just a variable reluctance sensor, something metallic moves inside the injector when the diesel flows which excites the VR sensor and you'll get a small AC waveform out of it, this will then be amplified/conditioned in the ECU and a DC square wave will be produced which goes to the micro.

Behind the injector pump you'll see two connectors (a black and a blue one if i remember correctly), ones your crank sensor and ones your needle lift sensor.

For the TPS, take a look by the side of your diesel filter if you see a white multiplug connector around that area that goes through a grommit in the bulkhead (to the right of the brake servo) you've got a TPS. I'm not so convinced though that these go "faulty" so to speak, to me as its a potentiometer if the windings become damaged then the resistance won't change at all - and if the resistance doesn't change the accelerator pedal does nothing. Try unplugging the TPS from the multi connector and you'll see what I mean. I'm presuming even with the check engine light on you can still drive the vehicle?

Matt.

You could carry on for ages supposing what has gone wrong,but until you stick it on Testbook and read you only be wasting time and effort.Bosch EDC codes are accurate - more than most.When you have read the codes you can then view whatever it is as live data to see whats going on.

thanks for the advise, its been fine since so hopefully it'll be ok but it needs the srs light resetting so i'll get them to fully check over it with the test book