Question

2001 Volkswagen Passat 1.8L with codes P0688 and P0171, what do the codes mean?

Answer 1

P0171 System too lean bank 1

P0688 ECM power relay sense

For P0171 you need to inspect for vacuum leaks especially at the MAF (mass air flow) air duct to throttle body,and also vacuum hoses causing false air,The fuel pressure will also need to be in proper orde the specification are 3.5 bar (50.7psi)

For P0688 This is supply voltage of engine control module (ECM) . The battery has to be at least 11.5 volts,the charging system has to be in working order and in the engine fuse junction box fuses # 15 and #30 has to have power and not be opened.

Answer 2

P0688 VOLKSWAGEN Code - Electronic Control Module Power Relay Control Circuit Open
Read more: https://www.autocodes.com/p0688_volkswagen.html

P0171 VOLKSWAGEN Code - System Too Lean Bank 1
Read more: https://www.autocodes.com/p0171_volkswagen.html