Question about the VW Jetta 2014 P0238 Boost Pressure Video

Hello everyone.

I have a question about Tommy's video concerning the VW Jetta Charge Pressure sensor fixed high.

I wanted to ask how would you guys go about resolving such an issue IF there was an absence of that voltage data PID? (EDIT: I realise I haven;t even checked my scan tool. Can you always view the V of any sensor on a car through the scan tool? I think not).

I came to realise that it would be very tricky for me. It wouldn't at all be intuitive to go through all the hassle of getting to the ECU to see whether or not there's an open in the wire. Maybe I'
m just not that experienced yet. ESPECIALLY that you can see those substituted values and it looks as if the sensor worked.

So, say that we had no PID, wouldn;t the only clue be in the wording of the fault? FIXED HIGH would mean probably that, the ECU see's it's bias V, therefore, bad sensor or open.

I can;t figure any sort of justiofication I could come up with. What if the ECU lived somewhere inside under the dashboard and it took an hour to get to?

Ok, so, I'd go about checking the sensor itself. If there is a 5v, is the ground <100mV, and that the signal is, indeed, 1,5V.

Now what? Unplug, no bias, 0V (since it's open). ok, fine, let's jump the 5v to the signal.

But that get's us nowhere since I don't see the PID. It would be 5V at the connector, though.

No signal circuit integrity testing possible!

Would I condemn a sensor immediately? I would hope that I wouldn't! Because there's nothing to lead me to that alternative. The signal plugged in is 1.5V, quite possibly that's correct, since we never want to see 5v/0v on a wire. Atmospheric pressure at KOEO.

Come to think of it... maybe I would rev the engine and see if there is any change in the signal at the connector.. just to exclude a faulty sensor.

Is there any other way? I guess not. Maybe I'm trying to process this to help me in the future in an absence of data PIDS. 

Sorry for the chaotic post, I'm just a bit stumped.

but, tbh, I think I have answered the question. If the sensor signal is fine, it changes, but the fault code is still there and it isn't about a performance issue... then really the only option is an open wire. That's just it. 

Ok, so, I've been giving it some thought.

How do we determine this is an actual wiring/sensor problem, or that the ECU is really trying to tell us that there is an overboost?

Would looking at actual live data be the only key? Specified and actual charge pressure? 

If the sensor and wiring was fine, then if it were an actual overboost, we would see SPECIFIED eg 15psi and ACTUAL eg 20psi. (driving the car and not just at idle).

On the other hand, in the video it looked like there actually was a discrepancy between actual and specified. Maybe a test drive would be necessary, to see what it looks like udner load (this data PID probably cannot be set during idle!)

Right? Then we know that there isn't any problem regarding the sensor/wiring?

Obviously we double check to make sure wiring is fine.

I'm guesing that checking the ECU would really be the only way of making sure what V the ECU was actually seeing if we had no data PID and a "FIXED HIGH" fault...

If it's what the sensor sees, then we can focus on the overboost itself.

urrgh, I don;t know why this is making my head spin.

Ok, so, I guess the approach would be is to understand what the DTC is trying to say.

FIXED HIGH

Either at some point in time it really did reach over 4.5V, possibly 5V max value and it triggered that DTC. If the sensor isn't stuck at 5V, then we would have to assume that there actually might have been an overboost.

So, test drive, actual/specified charge pressure data.

If it's fine, then wiring.

If there is more boost than what is specified, then we, apart from doing wiring checks, we have to be concerned about anything mechanical.

Maybe the wastegate, the vacuum lines, actuators, the n75 boost valve etc etc maybe even the turbocharger itself.

However, if the values are supposedly "fine", like in the video, BUT IT's IN LIMP MODE, then we might assume it's substituting the values from a broken sensor/wiring and sensing it into limp mode anyhoo.

Which would then lead us down the path of wiring even further. 
 

Because a "TURBOCHARGER BOOST SENSOR A CIRCUIT LOW"

would indicate it's stuck at 0v, probably an open/short. Right?

Someone, please help.

Ok, so, I finally got it. Hurrah!

Tommy's other video about a faulty Secondary Air injection Sensor came to the rescue.

In it, the code was a SHORT TO PLUS (high Voltage is what the ECU sees).

He backprobes the signal and, fair enough, there's 4.56V.

He unplugs it and it drops to 0.

Ok, but, how do we know if that's what the ECU is seeing?

Np bias, maybe there's an open in the signal wire? No data PID either.

Well, it flagged a short to ground now.

Which means that's another way of checking. I know that isn;t the same as the other case study I mentioned, but still. i would have been digging up the ECU by now and Tommy would have figured it out with a simple re-scan.

If the ECU is flagging a Short to ground, that means that it's seeing 0v, just like Tommy was at the connector.

So, I guess if you, in the Jetta case study, unplug the signal wire, it stays at 0v and you get no fault code "signal low" or "short to ground", clear codes, rescan, if it's still a Signal high with the sensor unplugged and with 0V at the connector., you know the ECU is seeing high V and there's an open.