F002: Pre-charging Fault

What F002 means in practice

Siemens OEM fault documentation describes F002 as a pre-charging fault: the monitored precharging period has expired and DC-link voltage did not reach its expected point. It is an enable-precondition failure, not proof that the inverter output bridge is defective.

This distinction saves expensive mistakes. If a technician repeatedly resets F002 or defeats the precharge path in an attempt to run the motor, a line-side, rectifier or capacitor defect can become a more destructive failure. The correct target is the path that establishes DC-link energy safely.

Evidence sequence before component decisions

First identify whether the installed unit receives AC supply directly or is a DC-AC inverter supplied from a common DC system. Then record fault value, type code, line-voltage context and whether the fault occurs immediately after energization or after a preceding modification. OEM guidance specifically directs checks of supply connection, fuses and consistency of unit identity information.

Only with safe isolation and verified discharge should the service path extend into precharge components, contactor sequencing, rectifier/DC feed integrity or DC-link capacitor condition. If a board was recently replaced, configuration mismatch and missing acknowledgement signals become part of the evidence set.

Repair or modernization outcome

A repair is justified when the failing precharge or supply component is identified and the link can be verified through controlled commissioning. A system assessment is more appropriate when precharge failure appears alongside obsolete hardware, undocumented modifications or recurring common-bus problems.

A useful support submission includes MLFB/type code, line or DC input configuration, fault value, photographs of accessible labels and a timeline of previous repair actions. That evidence can turn a vague “will not start” request into a targeted precharge or DC-link diagnosis.

Precharge failure modes to distinguish

A precharge fault may arise because the energy never reaches the DC link, because it reaches the link too slowly, because a downstream load or damaged capacitor prevents the voltage from establishing, or because the sequence and monitoring do not correspond to the fitted unit. These hypotheses require different evidence and make a generic “change precharge resistor” answer unsafe.

A technician should therefore record DC-link readiness behaviour through allowed diagnostic indications, the main-contactor sequence, visible fuse state, any recent unit or control replacement and whether the machine had previously suffered a bus or output-stage event. A failed output stage can impose an abnormal DC-link load; a failed contactor path can leave a healthy inverter unavailable.

Completion standard

The fault is not resolved when a reset succeeds once. A valid completion record must show that the correct configuration energizes repeatedly through its normal sequence, that DC-link-related faults do not reappear under intended operating conditions and that no protection device or temporary bypass remains defeated.

For a remote support request, photographs of the nameplate, accessible module labels and the displayed fault are useful; live internal voltage checks are not requested from unqualified users.

Workshop intake for an F002 unit

An F002 unit arriving at a workshop should be received with the fault display evidence, type code, input arrangement and the history of the failure: after long storage, after power outage, after board change, intermittent in production or suddenly permanent. Visual evidence of fuses, contactor/precharge hardware and DC-link area should be recorded before parts are removed.

Where a customer cannot provide measurements safely, the database should not request them. A technically credible intake asks for labels, display, event and visible condition; measurements of the DC link and internal precharge circuit belong to qualified repair procedures.

• Fault display/photo before clearing
• Failure timeline and recent repairs
• Input and cabinet topology
• Visual protection/precharge evidence
• Controlled test outcome after repair