MAP sensor wiring and diagnostic

[buzzboy]

I am seeing these codes which all lead me to issues with the MAP/IAT sensor. Everybody seems to say that the sensor itself is "never" the issue and I should look at wiring.
I can't find consensus on the pinout of the MAP sensor. The best thing I've found says
1: Ground
2: IAT output
3: 5v supply
4: MAP output

Then I checked each of them and got
Ground 0ohms referenced to chassis ground
IAT output 4.92v referenced to pin 1
5v supply 4.96v "
MAP output 5.65v "

I don't understand how the MAP output could be more than the 5v supply. I wonder if I have the pins wrong, or if that's my problem.

 

[TurboABA]

Are you looking at wiring diagrams or how are you trying to find out the pinout?

 

[P2B]

You reported P1592 Altitude Sensor / Boost Pressure Sensor: Implausible Correlation. This means that the altitude sensor (typically inside the ECU) and the MAP sensor did not agree at key on. You can check measuring blocks to confirm which one is out of range, but I suspect it will be the MAP given you also have an IAT code.

I don't understand how the MAP output could be more than the 5v supply.

It can't. The IAT output reading is also suspiciously high. I assume the readings were taken by backprobing? What are the readings at the connector when disconnected from the sensor?

 

[buzzboy]

Are you looking at wiring diagrams or how are you trying to find out the pinout?

I am trying to find the pinout by asking here. I have been searching this forum to no avail.

You reported P1592 Altitude Sensor / Boost Pressure Sensor: Implausible Correlation. This means that the altitude sensor (typically inside the ECU) and the MAP sensor did not agree at key on. You can check measuring blocks to confirm which one is out of range, but I suspect it will be the MAP given you also have an IAT code.

It can't. The IAT output reading is also suspiciously high. I assume the readings were taken by backprobing? What are the readings at the connector when disconnected from the sensor?

Those are the readings on the pins with the sensor unplugged. And that's IF I got the pinout correct. I will try backprobing the connector. I'm waiting on a new alternator so I checked it with the engine not running. I should have my new alternator in tomorrow then I can try it with the engine running.

 

[P2B]

Those are the readings on the pins with the sensor unplugged.

Voltage readings taken on the output pins without the sensor connected are not meaningful, but you can verify they aren't shorted to ground.

I suggest checking measuring blocks to see if the sensor outputs are plausible.

 

[buzzboy]

I ran these measuring blocks with the car idling.

 

[P2B]

Those numbers look reasonable, although 153 millibars (2.2psi) difference between atmospheric and manifold pressure at idle is higher than I would expect. Try comparing them with engine off. Maybe try fiddling with the sensor wiring while monitoring with VCDS to see if the values jump around.

 

[buzzboy]

I had my wife jiggle all the wires and the connector while I watched the values and saw no change. Very strange.
I haven't driven the car in a while, so I might go drive it and see if I'm still having driveability issues. I should probably log that drive.
Is it also odd that my fuel temp is super high? I know that's not right, as it showed that temp with a cold engine not running.

 

[tdi_my live]

Can you tell us the ECU number and the part number of the sensor? Then we can check whether the sensor is compatible with the car.

And in mwb10, with the ignition on but no idle, values 2 and 3 must be the same for the sensor to be compatible with the software.

 

[buzzboy]

This ECU and MAP are original to the car as best as I can tell.

MAP sensor: 038906051C
ECU VAG Number: 038 997 016 N

Is MWB10 short for Measuring Block 10? If so, that's my problem.

Atmospheric Pressure: 1006.2
Intake Manifold Pressure: 1181.7

 

[tdi_my live]

Sensor is 300kpa, software is stock for 300kpa
have you tried y new sensor?

 

[TurboABA]

have you tried y new sensor?

the sensor itself is "never" the issue

 

[buzzboy]

I have discovered the issue!
Sensor is a 3bar and the computer is tuned for a 2.5bar. I'll need to contact my tuner

 

[P2B]

I have discovered the issue!
Sensor is a 3bar and the computer is tuned for a 2.5bar. I'll need to contact my tuner

2.5 bar is stock for sensor and tune. Not sure why anyone would install a 3 bar sensor without a tune.

 

[buzzboy]

The dealer says that my tune is for a 3bar map. The paperwork when I got my ecu back from tuning said 2.5bar. I guess there's no way for a pleb to know what my tune actually is?

I found another thread on here about identifying knock off MAP sensors and it appears that my sensor is indeed original 2005 VWAG. I'll be near a junkyard tomorrow so I'll maybe see if they have MAP sensors. I almost want to grab a 2.5 and a 3 just to test back to back.

 

[P2B]

The dealer says that my tune is for a 3bar map. The paperwork when I got my ecu back from tuning said 2.5bar. I guess there's no way for a pleb to know what my tune actually is?

So they told you one thing and gave you paperwork saying something else? Maybe ask them to clarify?

You can log boost specified using VCDS to find out what the tune is actually requesting.

 

[caffeine]

I have discovered the issue!
Sensor is a 3bar and the computer is tuned for a 2.5bar. I'll need to contact my tuner

You have a BHW engine do you not? Stock MAP sensor for the BHW is 3 BAR. No BHW *ever* came with a 2.5 BAR MAP sensor.

2.5 bar is stock for sensor and tune. Not sure why anyone would install a 3 bar sensor without a tune.

2.5 BAR is NOT stock for the BHW. Stock for BHW is 3-BAR.

If your tuner made you a tune for a 2.5 BAR MAP sensor, I would find another tuner, unless there was some genuine misunderstanding of what engine they were making a tune for. The reason the BHW comes with a 3 BAR MAP sensor is because in stock form it runs too close to the limit of what a 2.5 BAR sensor can read. If your tune is actually made for a 2.5 BAR MAP sensor, you're either going to be down on power, or you'll have insufficient margin of error for overboost protection (in fact, the 'single value boost limiter' in the OEM tune is 2.62 BAR, i.e. over the limit of what a 2.5 BAR sensor can read).

Did this engine ever drive properly with this tune? Or is this like a swap that you're trying to get going properly? If there has always been a MAP sensor mismatch between the tune and the hardware, the engine would never have run properly. The MAP sensor is used for a lot.

 

[buzzboy]

This is a 2005 Passat BHW in a Mercedes. Pre tune/swap the Passat drove great. Post tune/swap I'm getting this DTC and power feels down. It's a Malone Stage 2 tune. The MAP sensor is stock and original.

I talked to the tune dealer today and he said my tune is for a 3bar MAP and that the documentation calling it a 2.5bar was a misprint. I don't know if I can confirm that from my end.

I'll try logging. What parameters should I log other than boost

 

[caffeine]

This is a 2005 Passat BHW in a Mercedes. Pre tune/swap the Passat drove great. Post tune/swap I'm getting this DTC and power feels down. It's a Malone Stage 2 tune. The MAP sensor is stock and original.

I talked to the tune dealer today and he said my tune is for a 3bar MAP and that the documentation calling it a 2.5bar was a misprint. I don't know if I can confirm that from my end.

I'll try logging. What parameters should I log other than boost

Do you have a way to revert to a stock tune? If so, you can do that, then check the measuring blocks again, key on, engine off, and the intake pressure should match atmospheric pressure. If the MAP sensor is still deviating from atmospheric, then your problem is in the MAP sensor or wiring. If the MAP sensor is reading as it should (almost exactly the same as atmospheric), then the problem is with the tune.

 

[buzzboy]

I don't have any way to revert to the stock tune. I had to send my ECU out. I'll see if I can find a 2.5bar today at the junkyard and go from there

 

[TurboABA]

I'll try logging. What parameters should I log other than boost

rpm, maf, requested and actual boost

 

[buzzboy]

I tried out a 2.5bar map and, as expected, it was also showing wrong pressure, but even more so.

Just gotta fix the brakes so I can take it out for a drive to log

 

[buzzboy]

I took it for a drive up to the gas station. Interesting that the sensor reads high at idle but as soon as I start driving it shows that I'm not getting nearly as much boost as requested. I cycled my N75 and heard the exhaust note change. I'll check that it's getting full travel next I guess?

 

[TurboABA]

That's a terrible log\chart... use something that makes it easier to review the data

TuneZilla Log Viewer

Visualize and share your datalogs with ease using this log viewer for VCDS, COBB, Edge EAS, ScanXL, ME7Logger, BlueDriver, and OBDeleven tools.

log.tunezilla.com

 

[buzzboy]

Sorry, new to this

Log #1018988

log.tunezilla.com

 

[TurboABA]

Check charge piping\circuit for boost leak.

 

[buzzboy]

Looks like part of my issue is the N75 not cycling. I tested it and it cycles when told to do so by VCDS. I also checked the travel by hand. I haven't touched the VNT actuator since buying the car.

Log #1020632

log.tunezilla.com

This snippet is a 2nd gear pull. It feels like it falls flat on it's face above 1800rpm, which makes sense if the N75 isn't doing anything.

 

[P2B]

Looks like part of my issue is the N75 not cycling. I tested it and it cycles when told to do so by VCDS.

It works when tested, so why would you conclude it doesn't?

 

[buzzboy]

When I log the N75 valve it's showing 9.9% all the time. This makes me think that the N75 isn't doing anything.

 

[P2B]

When I log the N75 valve it's showing 9.9% all the time. This makes me think that the N75 isn't doing anything.

Correct. The ECU isn't telling it to do anything because of the P1592 code.