http://wiki.ross-tech.com/wiki/index.php/17964/P1556/005462

17964/P1556 - Charge Pressure Control: Negative Deviation
Possible Symptoms

    Reduced power output
    Limp mode

Possible Causes

    Boost Pressure too Low [I believe this is wrong!]
    Hoses/Pipes incorrect connected, disconnected or leaking
    Charger Pressure Control defective
        VNT (variable nozzle turbo): nozzles stuck
    Solenoid Valve for Boost Pressure Control (N75) defective

Possible Solutions

    Check Hoses/Pipes to/between Components
    Check Solenoid Valve for Boost Pressure Control (N75)
    Check / Clean / Replace Charge Pressure Control
        Check / Clean mechanism for variable nozzles


http://wiki.ross-tech.com/wiki/index.php/17965/P1557/005463

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

    Reduced power output
    Limp mode

Possible Causes

    Boost Pressure too High [I believe this is wrong!]
    Hoses/Pipes incorrect connected, disconnected, blocked or leaking
    Charger Pressure Control defective
        VNT (variable nozzle turbo): nozzles stuck
    Solenoid Valve for Boost Pressure Control (N75) defective

Possible Solutions

    Check Hoses/Pipes to/between Components
    Check Solenoid Valve for Boost Pressure Control (N75)
    Check / Clean / Replace Charge Pressure Control
        Check / Clean mechanism for variable nozzles


...

so why is it that when i was getting underboost, i was throwing a pos deviation code?

http://nefariousmotorsports.com/forum/index.php/topic,871.0title,.html


I always thought pos deviation is lde>>0, neg deviation is lde<<0, where lde is (setpoint - process), NOT (process - setpoint).

Does ross-tech have it backwards?

Conclusion:

CLALDO (0x10710 index 0x63) can generate P1555 (0x12FDC)
CLALDRA (0x10713 index 0x66) can generate P1556 and P1557 (0x12FF4)

Note that 12FF4 contains
1557 1556 1556 1556

Which means the first entry is positive deviation (P1557), and the rest of the entries are negative deviation (P1556)

I do not know how minError/maxError in correlate with the various DTC slots yet.

As far as I can tell:

lde too positive (underboost: lde>EDLDRP) leads to LDRA MinError, which generates P1557, positive deviation
lde too negative (overboost) should generate P1556, negative deviation

However, according to the FR, only MinError can be set in dldr-ldra, so I'm not sure how P1556 is set, or even how entries other than the first in the manufacturer DTC can be generated.