There’s nothing more frustrating than a beautiful weekend morning, coffee in hand, only to have your trusty John Deere LA105 refuse to start. Before you call for expensive service or consider a premature replacement, take a breath. Most starting problems are caused by a handful of common, often fixable issues.

Let’s walk through the most likely culprits, starting with the simplest and most common fixes first. Grab your tools, and let’s get your mower back to life.

The Silent Treatment: Battery & Electrical Issues

Symptoms: You turn the key and hear only a single "click" or nothing at all. The dashboard lights may be dim or absent.

Troubleshoot & Fix:

Check the Battery Connections: Corroded or loose terminals are the #1 cause of "dead" batteries. Disconnect the cables (negative first!), clean the posts and terminals with a wire brush and baking soda solution, and reconnect them tightly.

Test the Battery Voltage: Use a multimeter. A healthy, fully charged battery should read ~12.7 volts. Anything below 12.4 volts needs a charge.

Charge It: Connect a smart charger. If it won’t hold a charge, the battery (typically lasts 3-5 years) likely needs replacement.

Safety Interlock Connection: While you're checking connections, ensure the wiring harness from the battery to the safety switches is secure.

The Hidden Guardian: Blown Fuse

Symptoms: Complete electrical failure—no lights, no click, no turnover. Everything is dead.

Troubleshoot & Fix:

Locate the Fuse: On the LA105, the main fuse is usually in a small in-line holder near the battery or attached to the starter solenoid.

Image Credit: Youtube Channel Real Man Skills

Inspect It: Pull the fuse and look for a broken wire or melted appearance inside the clear window.

Replace It: Always replace with a fuse of the exact same amperage (e.g., 20-amp). Having spares on hand is a great idea.

 The Operator Presence System: Seat Safety Switch

Symptoms: The engine cranks but won't fire up, or it starts and immediately dies when you release the key to the "run" position.

Troubleshoot & Fix:

Understand the Logic: This safety switch under the seat requires you to be sitting (or the switch depressed) for the engine to start and run.

Image Credit: Youtube Channel Redneck Computer Geek

Test It: Sit firmly in the seat, ensure the parking brake is set, and the PTO lever (blade engage) is OFF. Try starting.

Bypass Test (Carefully): You can temporarily unplug the connector under the seat and insert a small wire or paperclip to complete the circuit. ONLY do this for diagnostics. Never operate the mower with a bypassed seat switch on uneven ground.

The "Reverse" Surprise: Safety Interlock

Symptoms: Mower starts fine in neutral but won't crank at all when the gear lever is in reverse.

Troubleshoot & Fix:

This is a Feature, Not a Bug: Many mowers, including the LA105, have a reverse safety switch on the transmission. To start in reverse, you often must press and hold a "Reverse Implement" button or lever (usually on the dash) while turning the key.

Check the Manual: Review your operator's manual for the specific procedure.

Switch Failure: If it won't start in neutral either, this switch could be faulty and may need testing/replacement.

The Heart of the Matter: Fuel & Carburetor Issues

Symptoms: Engine cranks strongly but doesn't "catch," sputters, or only runs on choke. This is the most common issue for mowers that have sat with gas in them.

Troubleshoot & Fix:

Fresh Fuel First: Old, stale gas (over 30 days) is a killer. Drain the tank and refill with fresh, ethanol-free gasoline if possible.

Check the Fuel Shut-Off Valve: Ensure it's in the "ON" position.

Fuel Filter: Replace the in-line fuel filter if it looks dark or clogged.

Carburetor Cleaning: Gum and varnish from old fuel clog the tiny jets in the carburetor.

Add a quality fuel system cleaner (like Seafoam) to fresh gas and try running it.

As a last resort, the carburetor may need to be removed, disassembled, and cleaned thoroughly with carb cleaner. A replacement carburetor is also a relatively inexpensive option.

If you need a new carburetor for LA105 lawn mower, you can check the link here.

https://www.hipastore.com/products/hipa-carburetor-for-briggs-stratton-intek-14-5hp-21hp-carb-796109-591731-594593-new

The Spark of Life: Ignition & Spark Plug

Symptoms: Strong crank, good fuel delivery, but no start.

Troubleshoot & Fix:

Remove and Inspect the Spark Plug: Disconnect the wire, remove the plug with a socket wrench.

Check Condition: Is it fouled with black carbon? Wet with gas? Is the electrode gap extremely wide or the porcelain cracked?

Test for Spark: Reconnect the plug to its wire, ground the metal threads against the engine block (away from the hole!), and crank the engine. You should see a strong, blue spark. No spark means an ignition coil or safety switch issue.

Replace It: Spark plugs are cheap. Replace it annually with the correct type and gap it according to your manual.

Quick-Start Diagnostic Flowchart:

No Sound? → Check Battery & Fuse.

Cranks but Won't Run? → Check Seat Switch & Spark Plug.

Sputters/Dies? → Check Fuel (Fresh Gas, Filter, Carburetor).

Won't Crank in Reverse? → Engage Reverse-Operate Function.

Pro Safety Tip: Always disconnect the battery's negative terminal before working on electrical components, and never work on the fuel system near sparks or flames.

When to Call a Pro: If you've methodically checked all of the above and your LA105 still won't start, the issue could be a deeper electrical fault (bad starter solenoid, ignition switch, or safety switch) or internal engine problem. At that point, a certified John Deere technician is your best bet.

By working through this list, you’ll solve the vast majority of no-start problems yourself, saving time and money.