Reading drive fault codes when the manual's gone

It's 2am. The wrapper's stopped. The drive on the turntable is showing a four-character code and a flashing light. Nobody on shift has seen that code before.

The manual went years ago. Maybe it was in the panel door pocket until someone used it to wedge a fan. Maybe it was on a laptop that's since been wiped. Either way, you're stood in front of a drive with a code, a phone with one bar of signal and a shift manager asking how long.

This happens on plenty of sites with older kit. The good news is that a fault code is rarely a mystery for long. You need the right details, the right place to look and a bit of method.

Get the full model off the plate

The front of the drive tells you the brand and maybe a family name. That's not enough. Drives in the same family can use different code lists, and the same model can change between firmware versions.

Isolate and wait for the bus to discharge if you need to get close. Then read the rating plate, usually on the side. Write down:

1. The full part number or order code, every character of it
2. The serial number
3. The firmware or software version if it's shown, or if the keypad menu will tell you
4. The power rating and supply voltage

Take a photo of the plate as well. You'll want it for the next step and for the file.

Let the drive tell you first

Before you go looking anywhere else, see what the drive itself knows. Many drives have more on the keypad than the code on the front:

• A fault history or trip log menu, often with the last few trips listed in order
• A short text description alongside the code if you scroll or press the help button
• Values captured at the moment of the trip, such as output current, DC bus voltage, frequency or drive temperature

The trip log is worth its weight in gold. A drive that's tripped on the same code six times this week is telling you something very different from one that's tripped once.

If the drive has a PC tool and someone on site has the software and the right cable, that usually reads the log in plain words. Don't count on it at 2am, though.

Read the code by its family

Most drive codes fall into a handful of families. The exact numbers differ between makers, but the families are much the same. In our experience, the common ones are:

• Overcurrent, often shown with "OC" in it
• Overvoltage on the DC bus, often "OV"
• Undervoltage, often "UV", which usually means a supply problem or a dip
• Overtemperature on the drive's heatsink, often "OH"
• Earth or ground fault, often "EF" or "GF"
• Motor overload, worked out by the drive from current and time
• External trip, from an input wired to something else on the machine
• Communication loss, from a fieldbus or a keypad link
• Encoder or feedback faults on closed-loop drives
• Memory or parameter faults

So even a code you don't know may give you a clue from its letters. "OV" on a stop points you at the decel ramp and the braking resistor. Our guide to overcurrent, overvoltage and earth fault trips goes into the three you'll see most.

Treat this as a starting point, not a translation. Some makers use plain numbers with no letters. Some reuse letters to mean different things. Never act on a guess about what a code means if the fix involves changing parameters or working inside the panel.

Where to find the manual now

Most drive makers publish their manuals online, including for models they've stopped selling. Search on the full part number from the plate, not the family name. Go to the maker's own support site first. Forum posts and third-party PDFs can be for a different version, and a code list for the wrong firmware is worse than no list at all.

If the drive came as part of a machine, the machine maker may be the better call. They know which drive they fitted, how they set it up and what the external trip inputs are wired to. Our post on getting the most out of the machine supplier's helpline covers what to have ready when you ring.

You're meant to have the manual

Here's the part most sites forget. Keeping the manual isn't a nice-to-have. PUWER says people who use work equipment must have adequate health and safety information and, where appropriate, written instructions available to them (regulation 8). The PUWER code of practice says written instructions include the manufacturer's manuals (L22, paragraph 115)*. It also says maintenance instructions should be available or passed to the people who maintain the kit (L22, paragraph 116).

Makers and suppliers have their own duty to provide enough information, including drawings, for safe operation and maintenance. The code of practice tells you to check that they are provided (L22, paragraph 115). And it expects maintenance to follow the manufacturer's recommendations (L22, paragraph 74). Hard to do with no manual.

So a missing drive manual is a breakdown risk and a compliance gap at once. For whole machines with nothing left on file, read old machines with no manual.

The parameters are the other half

Finding the code is one job. Getting the drive back to how it was set up is another. If a drive has to be swapped, the new one needs the same parameters. Without a backup, someone has to rebuild them from memory or from the old drive, if it'll still talk.

Back up the parameters on every drive that can stop a line. Keep a copy off the drive and away from the machine. The same goes for PLC programs. Our post on the backups you'll wish you had covers both.

When to stop reading and call

A code you can't read is a dead stop. The line waits while someone scrolls forums on a phone. An engineer who knows that drive family can often tell you what the code means in a minute and what to check in five. That's the gap between a short stop and a lost shift.

Here's our view. If nobody on shift can tell you what a drive code means within the first half hour, call someone who can. Our 30-minute rule sets out why.

What to do on Monday

1. List every drive on your critical lines with its full part number, firmware version and a link to the maker's manual.
2. Save the manuals on site, somewhere the night shift can get to without a login they don't have.
3. Back up the parameters on each of those drives and store the files off the machine.
4. Print the fault code list for each critical drive and put it in the panel door.

* Paragraph numbers correct as of 10 September 2026 and refer to L22, fourth edition (2014, amended 2018). Check HSE's L22 page for the latest.