Touran 2006 1.9TDi Fault Code 18000 / P1592 MAP Sensor fault?

[frozenman77]

I'm having problems getting to the bottom of this problem. The car runs fine most of the time, but sometimes the engine management light comes on and car goes into limp (no turbo).

On scanning, the only codes are for No. 3 glow plug (opens circuit) and P1592 - Altitude Sensor/Boost Pressure Sensor - Implausible Correlation.

I checked the wiring loom / multi-plug to the MAP sensor, checked the earth is good and supply is stable at 5.0v. Because all this checked out, I decided to put a new MAP sensor in. However, the problem persists and I'm not sure what to try next?

Looking at the live data, there is a difference between the Barometric pressure (964 mbar) and the MAP sensor value (1061 mbar). This is with the ignition on but the engine not running. I assume the pressures should be the same (i.e. the MAP pressure should read the same as atmospheric without the engine running)? Is this enough to cause the fault and what could I try next?

Any thoughts much appreciated.

Thanks

[frozenman77]

Just done a lot of searching for similar problems. On some 2.0TDi engines there was a repair loom available for the MAP sensor. Does anyone know if a similar loom is available for the 1.9TDi BXE engine? Another owner reported that the MAP wiring can rub through somewhere under the battery tray causing a similar problem?

Does anyone know how different the barometric and MAP readings have to be before a fault code is triggered?

Cheers

[frozenman77]

Pulled the air box and battery out today. Found that the loom goes from the MAP sensor to a big multiplug junction on the nearside. Unplugged both ends and tested all wires for resistance. All showed 5 to 6 ohms apart from the brown earth wire that showed 56 ohms!

Getting hopeful, I made up a new earth wire and ran it along the path of the original loom, then checked live data. Oh dear!..... Barometric 969 mbar, but MAP value 1051 mbar! Still quite a difference.

Just for the hell of it I replaced the new MAP with the original one, and suddenly the Barometric was 969 mbar and the MAP was 969 mbar!!! Just shows you, new sensors are sometimes not tested properly. I'm reluctant to say it's definitely fixed, but will test drive over the next few days and confirm if it's solved for sure.

I would say thanks for all the help, but as yet, nobody else has commented! I guess it's not a well known complaint??

[Flash2]

Didn't you say you replaced the sensor because the correlation was implausible? Seems unlikely refitting the original sensor will have fixed the problem since it was that sensor that was logging the code in the first place.

The best way to test is to measure the voltage drop on the sensor ground. With the sensor connected back probe the red lead of your voltmeter into the sensor ground terminal (terminal 1). Connect the black meter lead to battery negative. See what reading you get when the ignition is switched on. If the ground is good, you should get < 0.1V. Anything higher than that means there is still resistance on the sensor ground.

The pressure sensor ground is shared with the intake air temp sensor. Checking the IAT data for a plausible reading can help confirm you have a ground issue. Best to test the temp reading before the engine has run so all the temperatures on the engine should be about the same. Compare the IAT, Coolant and Fuel temperature data pids. A bad ground on the pressure sensor will cause the IAT to be lower than the other temperature readings.

Regards.

Jim.

[frozenman77]

Didn't you say you replaced the sensor because the correlation was implausible? Seems unlikely refitting the original sensor will have fixed the problem since it was that sensor that was logging the code in the first place.
.

Thanks Jim, I only replaced the original sensor after finding a fault and running the new earth wire. Resistance on the earth between the two multiplugs I mentioned was 56 ohms, this reduced to only 5 ohms (same as the other 3 wires) after running the new earth so I knew I should have seen an immediate change in the MAP value. Because I didn't, I just tried the original MAP to see if the value changed. To my surprise, it did! Not only that, the Baro and MAP values identical! Fooled by two different faults?

Will confirm the IAT readings later when I test drive the car.

I'll check the IAT value as you suggest.

[Flash2]

Fooled by two different faults?

Ah, right. I see what your saying now.

I've just been dealing with a guy who has been having starting problems & rough running after fitting an ebay cam position sensor. When I compared the sensor output on the oscilloscope to a known good sensor I found the signal from the ebay part was inverted which was messing up the spark & injector timing. Definitely better to stick with dealer parts when it come to critical engine sensors.

[frozenman77]

Ah, right. I see what your saying now.

I've just been dealing with a guy who has been having starting problems & rough running after fitting an ebay cam position sensor. When I compared the sensor output on the oscilloscope to a known good sensor I found the signal from the ebay part was inverted which was messing up the spark & injector timing. Definitely better to stick with dealer parts when it come to critical engine sensors.

I drove it again today and so far everything seems good. All the sensor values are spot on. I think you're right about OE parts. Some things are worth risking a cheap one.....but not sensors!! (found out the hard way!).

Only fault I have left to fix is the permanent code for cylinder 3 glow plug. I've taken it out and it glows nicely connected to a 12v supply. I'm guessing another wiring issue, although I thought the supply wires were in series? Will investigate further tomorrow.

[Flash2]

Only fault I have left to fix is the permanent code for cylinder 3 glow plug. I've taken it out and it glows nicely connected to a 12v supply. I'm guessing another wiring issue, although I thought the supply wires were in series? Will investigate further tomorrow.

It's resistance the control unit uses to identify a faulty plug. You could try comparing the resistance of the cyl 3 plug to another known good one to see it there is any significant difference. The problem with that is most digital multimeters aren't very accurate measuring such low resistances. The other way you can test is by connecting a 12V bulb (test lamp) between battery positive and the terminal on each plug. A faulty plug will often make the bulb light much dimmer than a good one. The other alternative is to swap the cyl 3 plug to another cylinder then recheck the trouble code to see it if the code moves with the suspect plug to the other cylinder.