Hi

I am trying to decide how to approach solving my limp mode problem as described in this original thread:

Help diagnose limp mode 1.9 tdi - BRISKODA - The Skoda Forums

I have established a pattern where limp mode is accompanied by this dtc when asking for sustained high power overtaking on an uphill stretch of motorway:

17965/P1557/005463 - Charge Pressure Control: Positive Deviation

but is accompanied by this dtc when I hit the pedal hard and fast with the autobox (which is a bit clunky compared with some others I have driven) on a steep hill:

17563/P1155/004437 - Manifold Abs.Pressure Sensor (G71): Circ. Short to B+

I think I have a sticky vanes/actuator rod problem necessitating a reconditioned turbo, but the apparent electric fault is confusing. When checked by the local independent specialist on VAG cars he confirmed that the ECU was reading overboosting from the MAP even though on that occasion no clear cause (N75 valve, vaccum lines and actuator rod movement all checked out fine at the time) could be established and the car did not go into limp mode on a road test. I do however understand that the sticky vanes problem is very irregular and intermittent.

Trying to understand the German on the link from the ross-tech wiki page for the 17563 fault I can see that the G71 sensor is designed to send signals to the ECU between just above 0 at 200 mbar and just below 5 volts at 2500 mbar (i.e. a maximum of 1500 mbar or about 21-22 psi boost over atmospheric pressure). I also see that the German site lists 2 codes not in the ross-tech wiki - 17564 which google translates as "interruption/short to ground" and 17565 which google translates as "supply".

This is where I need some help from an auto electrician. Does the ECU throw a 17563 error if it sees 5v coming down the signal wire because this is what it would see if there was a true "short to B+" and is this the same signal the ECU would see if the charge pressure exceeded the MAP sensor design maximum of 2500 mbar? I ask this because what VAG-COM measuring blocks I have been able to do by reving up the engine not under load (my VAG-COM is on a desktop with an extended cable through the sitting room window, rather than a laptop) do show high spikes of the actual MAP against requested MAP. I am wondering if the apparent electrical fault is a red herring and the system is indeed overboosting beyond the MAP sensor design limit when the autobox kickdown jerks the system against the sticky vanes problem. I am also guessing that the 17564 dtc for circuit break/short to ground is generated by the ECU when it detects no volts signal coming from the MAP??

I may be talking out of my proverbial a*s" as it is a long time since I did electronics at school, but would appreciate any comments from an electrician on this before I spend £500 having a reconditioned turbo fitted that may not solve the problem.

Thanks in advance.

I would be 99% sure this is sticking vanes. If the thrust sensor G71 fails it tends to give a reading of 2800-2900mbar. Overboost (sticking vanes) gives around 2700mbar.

VNT units are available seperate from the turbo and are easy to change - not sure of a UK supplier, but this company in the US supplies them and they are not too dear..VW Volkswagen Turbocharger Turbo TDI, K03, K04, KP39A, T15, T3, KKK, Garrett, Passat 1.6 1.9, AAZ, ALH, 1Z, BEW 1V, MF, Jetta Rabbit Golf Quantum Passat VNT15 VNT17 Mercedes 300d

Should add that before you go off and buy anything you should (if not already done) check ALL the little vacuum pipes and suck and blow through them to make sure they are not blocked and have no splits.

Edited 9 October, 200916 yr by Hauptmann

would there be no benefit in stripping and cleaning the original VNT mechanism, there is a guide on one of the VAG forums on how to do it

Thought I would just post the final resolution of this. Tried a turbo cleaning kit from Innotec applied by local garage up the turbo's a*se - £90 in the money pit - both codes still there, still limp mode, still overboost showing in vag-com measured blocks. Tried MAP sensor replacement and all new wiring from sensor to ecu - £130 in money pit - as above. Tried replace all vacuum/air pipes and swap EGR with N75 (even though all had seemed OK on inspection) - £40 in money pit - as above. Tried exchange reconditioned turbo (nasty job for the fitter as no room to work with autobox gubbins in the way) - £600 but success - no limp modes, both codes gone, no overboost measured in vag-com. So for anyone who gets these 2 codes together, don't assume that the 17563 "map sensor short to positive" code is necessarily an electrical problem.

Just happened across some info from when I had the sticky turbo problem and those were the error codes I had, turbo removed, cleaned and replaced - problem gone.