U0174 Holden Hz or the Evaporative Emission Control System Incorrect Purge Flow is the set whenever the computer sees that there is a problem with the flow coming from the purge valve or the purge flow is not enough within the EVAP system. There are two wires dedicated for each coil; one is battery feed which usually comes from the distribution center, and the other one for the coil driver circuit from the PCM. The PCM grounds or ungrounds the circuit to activate or deactivate the coil.
Possible Causes :
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Look for damage to the tank indicating impact that may have damaged the fuel pump or sender. Now, clear the codes and test-drive the vehicle to see if the code is reset.
Diagnostic trouble code U0174 Holden Hz is not difficult to diagnose and repair. Thus, it always pays to have a qualified technician to look after your vehicle should this error code arise.
Diagnosing this code requires the engine to be in good running shape, without unmetered air entering the engine. If other codes that relates to misfiring condition, lean running or air entering the engine is present, then you must first fix those error codes before U0174 Holden Hz.
Fortunately, U0174 Holden Hz is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.