The Sevcon Gen4 drives AC traction motors in electric forklifts. When a fault occurs, it first protects the operator and the truck, sends an EMCY message on the CANbus, flashes the green LED and logs the fault. This guide summarises the fault codes from the Applications Reference Manual 177/52701 (Rev. 3.3) and the size 8 and 10 manuals.
Work on the traction battery, line contactor and fuse only according to the truck manufacturer's and the controller manufacturer's instructions.
How to read a fault
LED. A green LED on the housing stays lit while there is no fault. With a fault it flashes a fixed number of times, pauses and repeats the pattern. In multi-node systems only the affected controller flashes. The size 8 and 10 manual describes the LED indication explicitly for size 8.
DVT. Sevcon's Windows tool DVT shows status and the fault list.
CANbus. With any configuration software you can listen to the EMCY message or query objects directly. Object 5300h returns the active faults. Sub-index 1 gives the count. Write a position into sub-index 2 (0 is the highest priority) and sub-index 3 returns the fault ID. Object 5610h gives a plain text description when you write the ID to sub-index 1 and read sub-index 2.
The bus needs a 120 Ω termination at both ends. If the Gen4 is an end node, link pins 2 and 24 on the customer connector.
Fault categories
The manual defines five levels. They decide who can clear the fault.
| Level | Consequence | Cleared by |
|---|---|---|
| RTB (Return to base) | System shuts down immediately | Sevcon personnel |
| VS (Very severe) | System shuts down immediately | authorised service personnel |
| S (Severe) | System shuts down immediately | key switch off and on |
| DI (Drive inhibit) | Driving is prevented, braking still works | deselect all drive switches, then reselect |
| I (Information) | no immediate action, possible power cutback | not latched |
Fault table by LED flashes
The manual itself notes that a complete fault table is still to come, so check your firmware against current manufacturer documentation.
| LED | Fault | Level | First check according to the manual |
|---|---|---|---|
| 0 (off) | Internal hardware not operating | RTB | no user check given |
| 1 | Configuration item out of range, corrupt configuration data, hardware and software mismatch | VS | bring the value into range, object 5621h names the affected object |
| 2 | Direction selected with handbrake on, drive switch active at power up, seat fault, both directions for more than 200 ms, inch faults | DI | release handbrake, reset switches, check seat switch |
| 2 | Invalid steer switch states | VS | check steer switches |
| 3 | Fault in power stage (e.g. MOSFET short circuit) | VS | no user check given |
| 3 | Hardware over voltage | VS | reduce battery voltage below the maximum, check objects 2C01h and 4612h |
| 3 | Hardware over current | VS | check motor load, wiring and motor parameters |
| 4 | Line contactor welded or did not close | S | check contactor and wiring |
| 5 | Motor open circuit | S | check motor and wiring |
| 5 | Power steer module (PST) fault | DI | check the PST |
| 6 | Throttle above 20 percent at power up | DI | release the demand |
| 6 | Analogue input or output fault | VS | check input or output wiring |
| 7 | Battery empty, voltage too low | I | charge the battery, raise voltage |
| 7 | Voltage too high with contactor closed | I | reduce battery voltage |
| 7 | Voltage too high with contactor open | S | isolate the controller, investigate the high voltage |
| 7 | Precharge failure (capacitor below 5 V after precharge) | VS | check wiring for a short between positive and negative |
| 8 | Controller or motor too hot, controller or motor too cold | I | reduce load, let it cool or warm up, check motor thermistor |
| 8 | Heatsink over temperature | VS | remove load, let it cool down |
| 10 | Pre-operational, I/O initialising, RPDO timeout | I to S | DVT sets operational, check CANbus wiring and PDO configuration |
| 11 | Encoder fault (wire off, signals out of range) | VS | check encoder wiring, calibrate sin/cos signals |
| 11 | Over current or current control (PMAC motor) | VS | check motor load, wiring, motor parameters |
| 12 | Communication error | S | check CANbus wiring and CANopen configuration |
| 13 | Internal software or hardware, current sensor auto zero | RTB | no user check given |
| 13 | DSP parameter error | RTB | cycle the key switch |
| 14 | EMCY from a third party node | I to RTB | check CANbus wiring and the third party node |
| 15 | Service required | I | service the truck, reset service hours |
The size 8 and 10 manual also lists group 9 for a contactor coil short circuit, without set conditions.
Object 5100h sub-index 1 shows battery voltage at the key switch input, sub-index 2 shows capacitor voltage at the controller's positive terminal.
Line contactor, precharge and fuses
After power up the Gen4 first charges its input capacitors through the key switch line to an adjustable share of battery voltage (object 5820h, 50 to 90 percent). Only then does it close the line contactor. With several controllers, the master handles precharge for the slaves.
The manual assigns these Albright line contactors to the Gen4 peak output current. Never wire the coil to the supply side of the key switch. Use the output supply pins instead.
| Peak current | Coil | Catalogue number | Type per manual |
|---|---|---|---|
| up to 450 A | 24 V | 828/37024 | SW200-29 |
| up to 450 A | 48 V | 828/57026 | SW200-20 |
| up to 450 A | 80 V | 828/67010 | SW200-460 |
| up to 650 A | 24 V | 828/39001 | SW200 |
The main fuse can be mounted directly on the controller body. The B+ terminal is only a connection point for the fuse. If you connect the battery cable to the other end, the installation runs without a fuse.
| Input voltage | Peak current | Fuse | Catalogue number |
|---|---|---|---|
| 72 V and 80 V | 180 A | 200 A | 858/83339 |
| 36 V and 48 V | 275 A | 250 A | 858/29043 |
| 24 V and 36 V | 300 A | 325 A | 858/32044 |
| 72 V and 80 V | 350 A | 355 A | 858/32045 |
| 24 V to 48 V | 450 A | 425 A | 858/81990 |
| 72 V and 80 V | 550 A | 500 A | 858/32043 |
| 24 V to 48 V | 650 A | 750 A | 858/33021 |
Size the key switch fuse F2 for the larger of two values. The first is the sum of the drive currents plus 1 A for internal circuits. The second is the precharge demand. In the manual's example with two contactors at 2 A each, the result is 7 A.
Signal wiring
The manual specifies 0.5 to 1.5 mm² for signal wires. For CANbus and speed sensors it recommends twisted, shielded cable. The screen goes to the Gen4's negative terminal. The mating connector kit with 35 ways for signal wiring is 661/27091.
Matching parts from the catalogue
The linked parts come from our Sevcon catalogue. Check fitment before ordering against the type plate and the part number.
FAQ
What does it mean when the LED is steady or off?
A steady light means no fault according to the manual. No light is listed in the table as an internal hardware fault.
How do I clear a fault?
For S faults, switch the key switch off and on. For DI faults, deselect all drive switches and reselect. Authorised service personnel clear VS faults and Sevcon clears RTB faults.
What do I check at four flashes?
Four flashes point to a line contactor fault. Either the contactor was closed at power up or after the coil dropped out, or it did not close although the coil was energised. Check the contactor and its wiring.
Do you need one of the parts mentioned? We deliver the matching part with a quote the same day, and express shipping is possible.