I am new to the forum but have a confusing problem I hope someone can help me solve. My car has the ALH 90 bhp 1.9 TDI engine as in the mk4 Golf and several other cars, with an automatic gearbox.
I am trying to decide how to approach solving my limp mode problem as described in this original thread on another forum:
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, vacuum 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 Â£500 having a reconditioned turbo fitted that may not solve the problem.
Thanks in advance.