4.0TDI MAP Sensor Help
 

Hi all,

afraid I need some help please....

My car has thrown the flashing coil light - 4.0TDI and is in limp mode, i.e. no revs above 2.5kish rpm and loss of power.

It was fine this morning on the drive to work, happy as larry driving as normal. Needed to give a friend a lift at lunch, got in the car and flashing light and limp mode. No previous signs of issues or symptoms until failure.

Have read the codes, I only have 1 (well 2, but I don't believe the torque mount is relevant):

16620 - Manifold Pressure / Boost Sensor (G31)
P0236 - 001 - Implausible Signal - MIL ON
Freeze Frame:
RPM: 0 /min
Torque: 23.4 Nm
Speed: 0.0 km/h
(no units): 2.0
Raw, Index/Key Err.: 255 000 006
Raw, Index/Key Err.: 255 000 010
Absolute Pres.: 999.6 mbar
Absolute Pres.: 1111.8 mbar

It reads like a wiring fault as it's from 0rpm and 0 speed from the moment I turned the car on. If it was a true failing sensor i'd have expected intermittent boost faults, overboost, underboost, dropping into limp mode etc.

Can anyone help me narrow it down, please? I don't know where to find the sensors or their wiring. if it is the sensor i'm not shy of replacing a boost sensor, but again I dont know where it would be hiding.

Help... please?

Thanks! Ben

Hi Ben,

The charge pressure sender G31 is a single combined component with the intake air temperature sender G42. It's on the left side charge air cooler pipe.

Thanks Matty - any clues how this is accessed?

Sounds like it's probably either only accessible from underneath or it's a bumper off job?

is there one pr bank i guess? i dont know if that fault code tells me which bank it thinks has died?

It's accessible from underneath by removing the engine tray. Instructions attached +++

Thank you Matt. I'm still working on the assumption there is one of these per bank, so I've ordered two replacement sensors.

Thank you very much for adding instructions, the pictures are a bit weird but I think i understand where I'm looking... lets face it there are only two sets of charge pipes so its on there somewhere.

Thank you very much for your help.

Guys, I'm still stuck :-( Help!!

I found the boost sensor on the left (passenger) side no problem - changed that and it still shows an "implausible" fault. Clear it and it comes straight back the moment the ignition is turned on, even before the engine is cranked.

Is there a boost sensor for the drivers side circuit. I looked but couldn't find one. Had the bumper off and everything but just couldn't see another sensor in the pipe work.

Far as I can tell each bank of the V8 is it's own separate charge-air circuit so it would make sense to me that each side has it's own sensor. Am I wrong?

It's really gotten me down today! Wanted the car for Xmas and I need it in a week's time for holiday. Stress I really could do without.

Thanks in advance.

Hi there did you have a look at the workshop manual's on this site.

Yep it only details the one on left side - doesn't make mention of right side - so dont even know if it has one?

If there is only one sensor - which I've changed, twice - and that's not fixed it where do I go next?

Ben, There only is one. You need to VCDS scan, cycle and clear codes. It should be fine after that.
Steve

I did mate - cleared all the codes, more than once. Come straight back the moment the ignition is turned on, even if I don't turn the engine on! Is there something more, over and above clearing codes, that I'm supposed to do?

The only thing I can see is that the first absolute pressure value (999.6mbar) doesn't change. The other absolute pressure value does alter, but not that one. Don't know where this is being read from though.