Description

Komatsu FB15, FB18, FB50, FB10, FB14 1980 Troubleshooting Manual

You got an FB10 that steers like it’s fighting you. Or an FB50 where the EPS contactor trips as soon as you turn the wheel. Maybe you swapped the controller and it still acts up. That’s when you need the factory troubleshooting manual, not some aftermarket copy that guesses at voltages. This 29-page manual from 1980 is the exact document Komatsu gave its dealers for the FB10, FB14, FB15, FB18, and FB50. It walks you through the EPS system step by step, from contactor diagnostics to actuator disassembly. Don’t waste billable hours chasing ghosts.

Komatsu FB10 to FB50 Troubleshooting Manual: What’s Inside

Section 1 explains what EPS is and how it works — fail-safe function, controller logic, and the action of the electric motor. Section 2 gives you nine specific trouble-shooting procedures, each one covering a distinct failure mode: contactor won’t engage, immediate trip, trip on steering, no steering assist, hard steering, rough catch, vibration, self-steering, and motor overheating. Page 4 kicks off the actual diagnostics with a decision tree. I’ve seen techs waste a whole day on a contactor that just needed the ground cleaned because they skipped the factory sequence. That page alone pays for the manual.

Nine EPS Contactor Failure Scenarios

Every symptom in section 2.2 is laid out with probable causes and check points. For example, “EPS contactor (M7) trips as soon as wheels are steered” — the manual directs you to check the motor circuit, the torque sensor signal, and the controller input. It doesn’t just say “inspect wiring”. It tells you which terminals to probe and what resistance you should see. That kind of specificity is what separates an OEM document from a generic repair guide. If you’ve ever chased an intermittent steering fault on an FB18, you know the value of a factory flowchart.

Wiring Diagrams and Component Locations

Section 4 is pure gold: location of every component, pictorial wiring that shows actual connector shapes, and two wiring diagrams — one for EPS only and one for the chassis. Page 19 has the EPS-only diagram with wire colors and connector pin numbers. No guessing, no cross-referencing a third-party drawing that left out the ground path. This is the same schematic the dealer electrician used when the truck was new. Pair it with a Manual Transmission resource if you’re also dealing with drivetrain issues, but for steering electricals, this is the only document you need.

3 Steps to Disassemble the Actuator Assembly

Section 5 is the mechanical backbone of the manual. It tells you how to fix the actuator in a vice, remove the motor assembly, universal joint, cover, and idle gear. Then it covers inspection of wear limits and reassembly. Page 21 gives the step-by-step. I’ve seen guys try to pry the actuator apart without loosening the set screw — you’ll crack the housing. The manual saves you that kind of stupidity. Also includes the wearing limit for EPS motor brushes in section 3.2.

Why Use the 1980 Factory Manual Over Aftermarket Copies?

Aftermarket manuals for these old Komatsu forklifts often skip the fail-safe logic in section 1.4 or fudge the adjustment specs for the torque sensor in section 3.3. This is a factory publication, Pub. No. 90W-2201, printed September 1980. It’s 29 pages of original engineering data, not a reprint of a reprint. If you need the exact procedure for adjusting the actuator assembly after replacement, page 14 covers it. I’ve been turning wrenches for 28 years, and I will not trust a third-party document for EPS systems. One wrong spec and you’re replacing a controller.

Audience: Who Needs This Manual

Home garage guys who keep an FB14 forklift on the property will find this manual makes the difference between a running truck and a paperweight. Professionals in small shops that don’t have dealer-level diagnostic tools need the troubleshooting logic to isolate a bad torque sensor without a scope. The manual assumes you know basic electrical testing — it doesn’t teach you how to use a multimeter. It teaches you which pins to measure and what values to expect. For heavy-line overhaul, look at the KOMATSU FB12 FB15 FB18 Workshop Manual or the Komatsu FB10, AE50, AM50, FB10F, FB14F Workshop Manual – 361 Pages for engine and transmission work. The Komatsu FB15 FB18 FB18M FB20M FB10 Training Manual – 173 Pages is a good companion for operator-level training. For steering electricals, this troubleshooting manual is the one you keep on the toolbox.

FAQ

Does this manual cover the FB20 or FB25 models?

No, only the FB10, FB14, FB15, FB18, and FB50 are listed on the cover.

What should I do if the EPS contactor immediately trips?

Go to section 2.2, the second trouble-shooting procedure. It tells you to check for a short circuit in the motor winding, a faulty controller, or a seized actuator. You’ll need to measure resistance between the motor terminals — the factory spec is in the diagram. Also inspect the wiring harness for chafing near the frame. A tripping contactor on an FB15 often turned out to be a pinched wire at the steering column bracket. The manual walks you through voltage checks at the controller connector. Follow the sequence exactly; skipping the visual inspection step is a common mistake that leads to unnecessary part replacement.

Are wiring diagrams included?

Yes, section 4 has pictorial wiring and two full diagrams: EPS-only on page 19 and chassis on page 20. Wire colors and connector views are factory-correct.

Is this manual still useful for modern forklift repair?

If you run a shop that services older Komatsu models, yes. The EPS design on the FB series is fundamentally the same as later systems. The troubleshooting logic applies. For transmission-related questions, see Manual Transmission documentation.

Factory documentation is the difference between replacing parts and fixing the root cause. Access the Factory Manual and keep it on your bench. A 29-page investment that stops you from guessing on a system that can put a forklift down for days.