Audi
Boost pressure is below what the engine asked for (underboost). Common on TDIs; flat power and limp mode.
P1556 fault code: what it means
P1556: Boost pressure is below what the engine asked for (underboost). Common on TDIs; flat power and limp mode.
Usual causes, most likely first
- boost hose or intercooler leak
- sticking turbo vanes
- faulty boost control valve (N75)
- vacuum supply leak
P1556 by make
Skoda
Boost pressure is below what the engine asked for (underboost). Common on TDIs; flat power and limp mode.
Volkswagen
Boost pressure is below what the engine asked for (underboost). Common on TDIs; flat power and limp mode.
What the repair usually costs
- Automatic transmission rebuild, 6-speed and up (sent to specialist)NZ$7,190–NZ$13,080 · A$6,190–A$11,830
- DSG / dual-clutch mechatronic unit replacement (new or reman)NZ$4,300–NZ$7,160 · A$3,750–A$6,390
- DSG mechatronic repair / rebuild (unit sent to specialist)NZ$2,070–NZ$4,800 · A$1,890–A$4,250
- A/C compressor replace incl. drier and flush (European)NZ$1,560–NZ$3,200 · A$1,490–A$3,050
Not sure what P1556 means on your car? Ask Credov.
Before you clear it
Write the code down or photograph the scanner first. A code that comes straight back after clearing points to a fault that is still there. A car whose codes were cleared just before you arrived may be hiding one: the scanner's readiness monitors show "not ready" for a while after codes are cleared.
Researched by Credov from manufacturer and workshop sources. A fault code points to where a fault may be; a workshop confirms it with a diagnosis. Browse all fault codes.