Coherence Signals? Am I making sense...

[Rhothgar]

Evenin' all,

Just wondering if anyone has delved into how Bosch EDC15C2 gives out coherence signals.

According to t'internet, it is probably software related and the ECU is just monitoring signals from the sensors and checking they are within a certain range.

I ask because I've been cogitating about the coolant heater issue I have.

I'll try and do a video tomorrow of the continuity on one of the glow plugs. I reckon the fault is simply because one of the glow plugs can show 1 Ohm but can also show over 1 MOhm and sometimes OL.

I am actually coming around to the idea that it might not actually be internally shorted and I shall explain why in the video.

One thing I am unclear on is whether the Bosch EDC15C2 will clear any errors if the battery and the ECU have been disconnected for a length of time. Reason being is that I don't have a working Lexia at present.

[ozvtr]

One thing I am unclear on is whether the Bosch EDC15C2 will clear any errors if the battery and the ECU have been disconnected for a length of time.

Typically no. DTC's are usually held in nonvolatile memory (EEPROMS). Some, when set, must be cleared by a human hand (after the fault has been fixed). Some might clear after a number of start/drive cycles (after the fault has been fixed). But removing power won't clear any of them.
Most engine DTC's can be read and cleared by a generic OBDII reader. BUT ONLY ENGINE DTC's! However, the little 20pound OBDII reader can be quite useful. Don't underestimate it's potential! Remember, it's only good for engine DTC's.

[Rhothgar]

Thanks for that.

I saw a video on YouTube that showed codes clearing because of capacitor drain once battery was disconnected. Of course, that was on a certain make and model.

I suppose you are referring to P codes in that instance where you mention engine codes.

I also said coherence but in reality I meant plausibility test.

Done some more reading up but you never know if the source is 100%.

It was saying some faults might clear if the ECU sends a tiny current and it receives the expected response ie perhaps a 1-2 mV drop.

The issue is with my water coolant heater block. One of the glow plugs shows either 0.9 Ohm,
M Ohms or OL depending on whether I have the DMM on clean metal or on patch of rust.

The area of rust which is on the face when the wire touches is over about an eighth of the surface. Either that or an earth wire which I suspect is high resistance is probably the cause of the codes. P1403, P1404 and P1408.

I suspect the earth is more likely the issue and maybe the glow plug has I yet so resistance issues but I think I ruled that out almost.

[Rhothgar]

Well it was the earth. It had probably been arcing as the nut on the earth from the coolant block was not fully nipped up. Cannot believe that wreaked so much havoc. If it wasn't for the glow plugs sitting in water, it probably would have sent the car up in flames!