A Yaskawa drive carries a whole class of codes that flash the indicator, close a contact and keep the motor running, so a condition that stops the line on another platform shows up here while there is still time to do something about it, and that difference accounts for more of how these drives are regarded in a plant than the raw failure count does. The codes below are laid out in the order you meet them rather than alphabetically, and everything here holds for both the V1000 and the GA500 unless an entry says otherwise, since the two share one fault architecture across roughly a decade of product generations.
Before you clear anything
A reset erases the story, so before anyone touches the keypad it is worth writing down the code, what the motor was doing when it stopped, and what changed recently, because starting, accelerating, running steady, decelerating and sitting at power-up are five different answers and the drive will not tell you which one it was afterward.
Timing is the most underused clue in drive work, since a trip on acceleration points at ramp time and inertia and current limit, a trip at steady state points at load and cooling and sizing, a trip on deceleration points at regeneration, and a trip at power-up points at wiring and precharge and the supply. On a Yaskawa you do not have to reconstruct any of that from memory, because the drive recorded it for you, which the fault trace section further down covers.
Lock out and tag out before the enclosure comes open, verify the DC bus has discharged and honor the stated wait time before touching bus terminals, and match the PPE to the arc flash rating.
One fault language, two generations
The V1000 and the GA500 use the same fault taxonomy, the same mnemonic display codes, and the same fault trace and history structure in the U monitor parameters, so a technician who learned to read a V1000 in 2010 can read a GA500 today without relearning the vocabulary. The GA500 carries a longer list because it added features that needed codes, Bluetooth and comparators and the backup function among them, but the architecture underneath did not move, which matters when you are deciding whether a technique you learned on the older drive still applies to the one in front of you.
How Yaskawa tells you something is wrong
There are four named classes on these drives, and they behave differently enough that identifying the class comes before looking up the code.
A Fault shows the code with the ALM/ERR indicator illuminated steadily, shuts off the output so the motor coasts to a stop, and activates any multi-function output set to E for Fault, and the drive will not run again until somebody performs a Fault Reset.
A Minor Fault or an Alarm shows the code with the ALM/ERR indicator flashing while the drive keeps operating the motor, and neither one requires a reset because both clear themselves once the condition goes away. The two differ only in what happens on the contacts, since a minor fault activates a multi-function output set to 10 for Alarm while an alarm does not put out a minor fault signal at all.
An Operation Error, called a Parameter Setting Error on the GA500, means two parameter settings conflict or a setting does not match the hardware fitted, and the drive will not run until they are corrected, while an Auto-Tuning Error means the tuning routine aborted and has to be run again.
The GA500 publishes 78 faults, 55 alarms, 28 auto-tuning errors, 12 parameter setting errors, 10 backup function errors and 4 informational displays, which comes to 187 classified entries across 157 distinct codes on the keypad.
The same mnemonic often appears twice, once as an alarm and once as a fault, each carrying its own hex code that a controller reads over Modbus, so that CE is 0014 as an alarm and 0021 as a fault, bUS is 0015 and 0022, boL is 0045 and 004F, and oH is 0003 as an alarm and 0009 as a fault with oH1 at 000A as the fault-level heatsink code. The technician standing at the keypad learns one word per condition and reads severity off the indicator, while the controller sees two separate register values and can trend or annunciate a warning without the drive ever tripping.
The quick table
The operational codes you meet on a running machine. Where a code appears in both columns, the same condition exists at two severities.
| Code | Name | Alarm (hex) | Fault (hex) |
|---|---|---|---|
| bb | Baseblock | 0008 | |
| boL | Braking Transistor Overload | 0045 | 004F |
| bUS | Option Communication Error | 0015 | 0022 |
| CALL | Serial Comm Transmission Error | 001D | |
| CE | Modbus Communication Error | 0014 | 0021 |
| CF | Control Fault | 0025 | |
| CoF | Current Offset Fault | 0046 | |
| dEv | Speed Deviation | 0011 | 0019 |
| EF | FWD/REV Run Command Input | 0007 | |
| EF0 | Option External Fault | 001A | 0027 |
| EF1 to EF7 | External Fault, terminals S1 to S7 | 0009 to 0015 | 0039 to 0043 |
| GF | Ground Fault | 0006 | |
| LF | Output Phase Loss | 001C | |
| LF2 | Output Current Imbalance | 0036 | |
| LSo | Low Speed Motor Step-Out | 0051 | |
| oC | Overcurrent | 0007 | |
| oH | Heatsink Overheat | 0003 | 0009 |
| oH1 | Heatsink Overheat | 000A | |
| oH3 | Motor Overheat | 001D | 0022 |
| oH4 | Motor Overheat Fault, PTC input | 0020 | |
| oL1 | Motor Overload | 000B | |
| oL2 | Drive Overload | 000C | |
| oL3 | Overtorque Detection 1 | 0005 | 000D |
| oL4 | Overtorque Detection 2 | 0006 | 000E |
| oL5 | Mechanical Weakening Detection 1 | 003D | 0044 |
| oPr | Keypad Connection Fault | 001E | |
| oS | Overspeed | 0010 | 0018 |
| ov | Overvoltage | 0002 | 0008 |
| PF | Input Phase Loss | 0047 | 001B |
| rH | Braking Resistor Overheat | 0010 | |
| rr | Dynamic Braking Transistor Fault | 000F | |
| SC | Short Circuit / IGBT Failure | 0005 | |
| SEr | Speed Search Retries Exceeded | 003B | |
| SToF | Safe Torque OFF Hardware | 003B | |
| STPo | Motor Step-Out Detected | 0037 | |
| UL3 | Undertorque Detection 1 | 001E | 0029 |
| Uv | Undervoltage | 0001 | |
| Uv1 | DC Bus Undervoltage | 0002 | |
| Uv2 | Control Power Undervoltage | 0003 | |
| Uv3 | Soft Charge Answerback Fault | 0004 |
Four further families sit behind these and belong to commissioning rather than to running: CPF00 through CPF38 for control circuit errors, oPE01 through oPE33 for parameter setting conflicts, End1 through End9 and Er-01 through Er-25 for auto-tuning, and a set of backup function errors. They are covered as groups near the end.
The code is the back end of the job
This page gets you through the fault in front of you. Before the First Fault is the full reference, plus the install and commissioning practice that stops most of these from happening at all.
The fault details
Uv1, Uv2 and Uv3, the three undervoltages
What it means. Yaskawa splits undervoltage three ways according to which supply actually failed, so that Uv1 is DC Bus Undervoltage, Uv2 is Control Power Undervoltage, and Uv3 is a Soft Charge Answerback Fault, meaning the precharge circuit never reported back that it closed.
Most likely cause. Uv1 points at a phase loss in the drive input power or a sag on the incoming line, Uv2 points at the control power supply itself with the ride-through setting in L2-02 as a contributing factor, and Uv3 points at damage to the relay or contactor in the soft-charge circuit, which is a component inside the drive rather than out in the plant.
The fix, in order. For Uv1, correct any wiring errors on the main circuit input power and measure all three phases at the drive terminals rather than at the disconnect so the wiring between them is part of the test. For Uv2, work the control power path and consider whether a momentary power loss recovery unit belongs on the drive. For Uv3, re-energize once, and if it returns the soft charge circuit is damaged and the drive needs service.
Worth knowing. Most drives give you one undervoltage code and leave you to work out whether the bus sagged, the control supply died, or the precharge contactor failed to pull in, so having that answer off the display before anything comes apart is worth the time it saves.
oC Overcurrent
What it means. Output current exceeded the drive’s limit, which is the fast trip protecting the power devices.
Most likely cause. The manual leads with the load being too heavy, and behind that sits the usual family of a short circuit, a ground fault on the output, or an acceleration ramp asking for more current than the drive will supply.
The fix, in order. Measure the current going into the motor rather than assuming what it is, then disconnect the motor leads at the drive and megger the cable and the motor separately, since resetting repeatedly into a short is how a repairable drive becomes a replaced one. If both test clean, look at what the load does in the instant before the trip rather than at what it does while running.
SC Short Circuit and IGBT Failure
What it means. A short circuit was detected or an output device failed, and Yaskawa names both possibilities in the one code.
Most likely cause. The manual points first at overheating that damaged the motor or the motor cable, which puts the insulation ahead of the drive in the order of suspicion and is worth respecting.
The fix, in order. Measure the motor insulation resistance and replace the motor if it has failed, check the cable separately, and bring the drive output stage into question only after both of those test clean.
When to stop. SC and oC appearing together on the same machine, particularly after a stretch of high ambient temperature, usually means the insulation went first and took the output stage with it.
GF Ground Fault
What it means. Current found a path to ground on the output.
Most likely cause. Overheating that damaged the motor or the motor cable, moisture, or insulation that has been degrading quietly for a while.
The fix, in order. Measure the motor insulation resistance and replace the motor if it fails, megger the cable separately so you know which of the two you are dealing with, and open the peckerhead and look while you are there, since water and corrosion are visible and cost nothing to check.
Worth knowing. Yaskawa gives you a single GF with no leg named, where an Allen-Bradley PowerFlex will tell you the phase, so this is one comparison that runs the other way.
PF Input Phase Loss, LF Output Phase Loss and LF2
What it means. Yaskawa separates the input side from the output side, PF for a phase lost coming in and LF for one lost going out, with LF2 covering an output current imbalance that has not fully opened yet.
Most likely cause. PF comes from a phase loss in the drive input power, which usually means a fuse or a line side connection, while LF comes from a disconnected motor main circuit cable or a wiring error, and LF2 is a partial version of the same thing.
The fix, in order. For PF, correct the input power wiring and check the fuses individually, because one open fuse is the classic cause and does not announce itself. For LF and LF2, examine the output wiring for errors or disconnected conductors and torque the terminations at both ends.
Worth knowing. LF2 is the useful member of the group, since an imbalance that has not yet become an open circuit is the early stage of a connection that will fail, and finding it there costs less than finding it at LF.
oL1 Motor Overload and oL2 Drive Overload
What it means. Yaskawa separates what is overloaded, with oL1 covering the motor and oL2 covering the drive itself.
Most likely cause. The manual leads with the load being too large on both, though on oL2 an aggressive acceleration ramp and degraded cooling both contribute.
The fix, in order. Decrease the load, and on oL1 confirm the motor protection settings match the nameplate before concluding the load is at fault, since a wrong setting produces this code with nothing mechanically wrong. On oL2, check the sizing against the real duty cycle rather than against the motor nameplate, because those are two different questions.
oL3 Overtorque and UL3 Undertorque
What it means. These two are a mirror pair, oL3 detecting more torque than expected and UL3 detecting less, and both exist as an alarm and as a fault so they can be set to warn rather than trip.
Most likely cause. The manual says the same thing for both, that a fault occurred on the machine, which is the useful part, since neither code is about the drive.
The fix, in order. Examine the machine and remove the cause, working from the observation that undertorque generally means something came loose or broke while overtorque generally means something is binding.
Worth knowing. Setting these as alarms rather than faults turns a general purpose drive into a condition monitor for the driven machine, and the function does nothing at all until somebody configures it.
oH and oH1 Heatsink Overheat, oH3 and oH4 Motor Overheat
What it means. Four codes across two locations and two severities, where oH is the heatsink overheat alarm and oH1 is the fault-level version of the same condition, while oH3 is a motor overheat alarm and oH4 is the motor overheat fault taken from a PTC input.
Most likely cause. For the heatsink pair, a high ambient temperature the heatsink cannot shed, which means dirty fins, a failed fan, a hot cabinet, or a carrier frequency set high in an enclosure that cannot carry the extra switching loss. For the motor pair, an overloaded motor, a ramp that is too aggressive, or a motor running slowly without enough cooling for the current it is carrying.
The fix, in order. Measure the actual ambient at the drive intake rather than in the middle of the room, since those two readings sit well apart in most plants, then clean the heatsink, confirm the fan turns and turns the right direction, and look at where the carrier frequency is set. For the motor codes, check the load level, the acceleration and deceleration times, and the motor itself.
Worth knowing. The two heatsink codes work as a sequence, in that you get the alarm with the motor still running and only get the fault that stops it if the condition continues, which is time a drive without an alarm tier would not have given you.
rH, rr and boL, the braking family
What it means. Three codes for three separate parts of the braking circuit, with rH for Braking Resistor Overheat, rr for a Dynamic Braking Transistor Fault, and boL for Braking Transistor Overload.
Most likely cause. rH comes from a deceleration time that is too short and excessive regeneration, rr comes from damage to the drive control circuit, and boL comes from a braking duty cycle higher than the transistor was built for, meaning too much regeneration power or too high a repetition frequency, or from the protective function being left enabled when a regenerative converter is fitted.
The fix, in order. For rH, check the load level, the deceleration time and the speed, and lengthen the ramp before adding hardware. For boL, install a regenerative converter or increase the deceleration time, and if a regenerative converter is already fitted then set L8-55 to 0 to disable the internal transistor protection. For rr, re-energize once and replace the drive if it comes back.
When to stop. A load with real inertia behind it that has to stop fast is a braking sizing problem, so lengthening the ramp only moves the trip until the process will not tolerate any more ramp.
ov Overvoltage
What it means. DC bus voltage went above the limit, and it exists as an alarm at 0002 and a fault at 0008.
Most likely cause. The manual leads with a deceleration time that is too short, letting more regeneration back into the bus than the drive can absorb.
The fix, in order. Increase the deceleration time in C1-02, C1-04, C1-06 or C1-08 depending on which ramp is active, and if the process will not tolerate a longer ramp then the energy needs somewhere to go, which means a braking resistor rather than further tuning. At steady state or idle, measure the incoming line voltage and check the transformer tap.
EF and EF0 through EF7, the external faults
What it means. EF on its own means a forward command and a reverse command arrived at the same time, EF0 is an external fault coming through an option card, and EF1 through EF7 are external faults arriving on input terminals S1 through S7, one code per terminal.
Most likely cause. EF is a sequence problem in whatever is commanding the drive, while the numbered ones mean the device wired to that terminal did what it was installed to do.
The fix, in order. For EF, examine the forward and reverse command sequence and correct it. For EF1 through EF7, the terminal number tells you which circuit to go and trace, so you walk to the right device instead of working the whole chain.
bb Baseblock
What it means. An external baseblock command was received, which gates the output off without anything having failed.
The fix, in order. Examine the external sequence and the timing of the baseblock command, since this is nearly always a control logic question rather than a drive question.
CE, bUS and CALL, the communication codes
What it means. CE is a Modbus communication error, bUS is an option communication error meaning the drive received no signal from the controller, and CALL is a serial communication transmission error, with CE and bUS both existing as an alarm and as a fault.
Most likely cause. Incorrect communication cable wiring, a short in the cable or a cable not connected, and electrical interference, which the manual treats at length and which is the repeat offender in this whole family.
The fix, in order. Correct the wiring and repair or replace the cable, then work the interference, which means examining the control circuit lines and main circuit lines and ground wiring, keeping communication wiring separated from drive power lines, using shielded cable grounded at the controller or the drive input side, and checking whether a magnetic contactor is the source and needs a surge protective device. On bUS, confirm the option is correctly installed before replacing anything.
Worth knowing. F6-01 sets what the drive does with the motor when it detects a communication error, and that parameter deserves a deliberate decision rather than whatever it shipped with, since it decides whether a dropped packet stops your process.
SToF Safe Torque OFF Hardware
What it means. The safe torque off circuit reported a hardware level problem, specifically that only one of the two terminals H1-HC and H2-HC received the disable signal.
The fix, in order. Confirm the Safe Disable signal is arriving from the external device on both channels, and trace the safety circuit rather than working the drive.
Worth knowing. A discrepancy between the two channels is a different condition from both channels opening normally, and the drive separates them, which is the behavior you want from a safety function. Jumpering a safety circuit to clear a code is not troubleshooting.
oS Overspeed and dEv Speed Deviation
What it means. oS means the motor ran faster than allowed and dEv means actual speed drifted too far from commanded speed, and both exist as an alarm and as a fault.
Most likely cause. oS comes from overshoot in the speed loop, while dEv comes from a load too heavy for the drive to hold at the commanded speed.
The fix, in order. For oS, decrease the proportional gain in C5-01 and increase the integral time in C5-02 to settle the loop. For dEv, decrease the load, then check whether the acceleration and deceleration times are realistic for the inertia involved.
oL5 Mechanical Weakening Detection
What it means. The drive detected overtorque matching the pattern it was configured to watch for as mechanical deterioration, and it exists as both an alarm and a fault.
The fix, in order. Run a deterioration diagnostic on the machine side, since the code is pointing at the driven equipment rather than at anything electrical.
oPr Keypad Connection Fault, CF Control Fault and CoF Current Offset Fault
What it means. oPr means the keypad is not securely connected, CF means the control loop lost control of the motor with the manual pointing first at motor parameters set incorrectly, and CoF means the drive started while an induced voltage was present, which happens on a motor that is still spinning.
The fix, in order. For oPr, examine the connection between keypad and drive. For CF, set the motor parameters correctly and run Auto-Tuning again. For CoF, build a sequence that does not restart into a spinning motor, or use speed search so the drive picks up the running shaft instead of fighting it.
The CPF, oPE, End and Er families
What it means. These four groups are commissioning and internal codes rather than running codes, where CPF00 through CPF38 are control circuit errors including EEPROM data errors and terminal board connection errors, oPE01 through oPE33 are parameter setting errors meaning two settings conflict or a setting does not match the hardware fitted, and End1 through End9 with Er-01 through Er-25 are auto-tuning results and errors.
The fix, in order. For a CPF code, cycle power once and replace the drive or the affected board if it returns. For an oPE code, the drive is telling you which parameter group disagrees with which, so read the code and fix the conflict rather than defaulting the drive and losing the setup. For a tuning code, correct the nameplate data or the coupling state and run the tune again.
The faults you prevent are the ones you never read
The drive keeps two separate records, and between them they answer most of what a technician wants to know after a trip.
U3 is the fault history, holding the 1st through 10th most recent faults in U3-01 through U3-10, with the elapsed operating time at each of those ten in U3-11 through U3-20.
U2 is the fault trace, and it captures 20 values at the fault itself: the current fault and the previous fault, the frequency reference, output frequency, output current, motor speed, output voltage, DC bus voltage, output power and torque reference at the fault, the input terminal status and the output terminal status at the fault, the operation status, the elapsed time, the SFS output, the q-axis and d-axis currents, the control deviation, the heatsink temperature, and the STPo detection value.
The input and output terminal status pair repays attention, because it records which digital inputs were energized at the instant the drive stopped and which outputs it was driving, which settles whether the permissive was actually made and whether the run command was present without a scope and without instrumenting anything, and neither a PowerFlex 525 nor an ABB ACS380 captures the state of the I/O at the trip.
All of it is parameter data, so a controller can read it, and a plant running these on a network while pulling only a fault bit is leaving the trace and the history unused.
Reading and clearing faults
A fault requires a Fault Reset before the drive will run again, and the multi-function output set to E for Fault stays active while it stands, while a minor fault or an alarm needs no reset at all, since removing the cause clears it and the motor never stopped in the first place.
The multi-function outputs are where the warning tier becomes worth something, because setting H2-01 through H2-03 to 10 for Alarm gives you a contact that closes on a minor fault while setting one to E gives you the fault contact, so a plant that wires the alarm contact hears about a developing condition while the line is still running and a plant that wires only the fault contact hears about it after the stop.
Before clearing anything, read U2 and U3, since the history tells you whether this is the first time or the tenth and the trace tells you what the drive was doing when it happened.
Where this fits
Fault codes are the back end of the job, and most of what appears on this page was decided months earlier by a cable length, a grounding choice, a cabinet without enough air, or a sizing calculation run off the motor nameplate instead of the duty cycle. If you want fewer of these, the work happens before the first start, which is what the VFD Installation Guide and the VFD Troubleshooting Guide are built around, and the PowerFlex 525 Fault Field Guide and the ABB Drive Fault Field Guide cover the same ground on those platforms.
If what you want is the competency behind the codes rather than the codes themselves, that is what the training does, and Before the First Fault is the field record the whole approach came out of.
Fault codes and behavior on this page are taken from the Yaskawa GA500 Technical Reference and the V1000 Technical Manual. Confirm against the manual revision that matches the software version in front of you. Yaskawa, V1000 and GA500 are trademarks of Yaskawa Electric Corporation, used here for identification.