Description

Komatsu D31EX, D37EX, D39EX, PX-21 Service Manual

I’ve seen too many guys pull a head gasket job on a D37EX using some aftermarket PDF they found online, then wonder why the final torque spec was wrong and the block cracked. That’s not happening with this manual. This is the original Komatsu Service Manual – 258 pages of factory-sourced documentation for the Komatsu D31EX, D37EX, D39EX, PX-21 Service Manual. No reprints, no third-party edits. You get the same specs the dealer techs use.

258 Pages of Factory Operation & Maintenance

Every page in this manual came from the same press that printed the copy sitting in the cab of a new D31EX. It covers the D31EX, D31PX, D37EX, D37PX, D39EX, and D39PX models with specific serial number ranges. The D31EX-21 starts at 50501 and up; D37EX-21 from 5709; D39EX-21 from 1501. That matters when you’re ordering parts or looking up a bulletin. The foreword on page 3 tells you exactly where to store the manual – pocket behind the operator’s seat or inside the right/left doors if cabs are equipped.

What the Safety Section Actually Covers

Page 5 kicks off the safety information with signal words, noise and vibration levels for the D37EX and D37PX, and a guide to reduce vibration. If you’ve ever had a service writer hand you an aftermarket manual that skipped the safety labels section, you’ll appreciate that this one includes exact positions of safety pictograms, general precautions, and maintenance precautions. The warning on page 1 is clear: unsafe use can cause serious injury or death. Operators and maintenance personnel must read this manual before touching the machine.

Engine Serial Number Location and Machine Identification

You need the Engine serial number plate location to verify correct parts. This manual walks you through the product identification number (PIN), the machine serial no. plate, and the position of the service meter. It even includes a table for entering serial numbers and distributor info. That level of detail is what keeps you from ordering the wrong injector or pump. For a broader reference, check out the Komatsu D31 D37 2004 Workshop Manual for additional service procedures on these models.

3 Reasons to Stick with OEM Documentation

• Torque values are factory-sourced – not guessed from a generic chart. When the manual says 40 Nm on a transmission bolt, that’s what Komatsu engineers wrote.
• Wiring diagrams and hydraulic schematics match the actual machine. Aftermarket reprints often reverse pinouts or miss updated bulletins.
• Safety warnings are specific to the D31EX/D37EX/D39EX series. You get the tow hook ratings, battery handling steps, and cold weather starting procedures that keep you alive.

If you’re working on a manual transmission variant, the Manual Transmission section gives the factory shift linkage adjustment and gear oil capacity. Another external resource on Manual Transmission from Wikipedia can help with general theory, but for this machine, use the Komatsu spec.

Cold Weather Operation and Long-Term Storage

The operation chapter covers starting in cold weather, warming up, and a specific procedure for cold weather after completion of work. It also details long-term storage – before, during, and after. That section saved me a frozen starter motor on a D39EX that sat for three months. The troubleshooting section includes what to do if the battery is discharged, how to tow the machine when the engine doesn’t start, and even the procedure for releasing pressure in the accumulator circuit.

Related manuals you might need: KOMATSU D31EX PX-21 D37EX PX-21 D39EX PX-21 Operation & Manual for daily checks, and Komatsu D31EX D31PX D37EX D37PX D39EX 2007 Workshop Manual for overhaul specs.

FAQ

Does this manual cover the D31EX-21 with serial number 50501?

Yes. The serial number range is listed on page 1 – D31EX-21 from 50501 and up. If your machine falls outside that, verify with Komatsu.

What is the difference between this Operation & Maintenance Manual and a Service Manual?

This manual covers operation, safety, daily maintenance, troubleshooting, and transportation. A service manual goes deeper into disassembly and repair of the engine, transmission, and hydraulics. For heavy rebuilds, you’ll want the workshop manual.

Can I use this manual for a D39EX-PX-21?

Yes. The D39EX and D39PX are covered. Page 1 lists D39EX-21 from 1501 and up.

How do I find the engine serial number on a D37EX?

The manual shows the engine serial no. plate location in the necessary information section. It’s typically on the valve cover or block, but check the diagram for your specific engine family.

Access the Factory Manual and keep it in the cab or on your tablet. You’ll have every spec, every warning, and every procedure Komatsu intended for these machines.