Most TJ problems I've chased down started as a skipped maintenance item three years earlier. This checklist is built around the 4.0L's known wear points, not just the generic factory schedule — use it as a second opinion alongside your owner's manual.
30,000 mi
Spark plugs & wires inspectionView Part →
Transmission fluid checkView Part →
Differential fluid check (both axles)View Part →
Air filter replacementView Part →
60,000 mi
Spark plugs replacementView Part →
Coolant flushView Part →
Ball joints inspectionView Part →
Crank position sensor connector checkView Part →
Serpentine belt inspectionView Part →
100,000 mi
Timing chain inspection (known 4.0L wear point)View Part →
Water pump replacementView Part →
Radiator hoses replacementView Part →
Front axle U-joints inspectionView Part →
ASD relay testView Part →
150,000 mi
Full harness inspection (chafe points, ground straps)View Part →
Blower motor current draw testView Part →
Motor mounts inspectionView Part →
Fuel pump pressure testView Part →
From the bench
The harness inspection at 150k isn't optional if you're chasing electrical gremlins earlier than that. A lot of "random" TJ electrical problems trace back to chafed wiring in the same handful of spots — catching it during routine maintenance is a lot cheaper than diagnosing a full crank-no-start later.
Related Guides
Already past 150k and fighting an electrical gremlin? Start with the TJ Won't Start Diagnostic Guide for the triage order that actually finds it.
Affiliate Disclosure: Doc's Garage is a participant in the Amazon Services LLC Associates Program. Links on this page may earn a small commission at no extra cost to you. I only recommend parts I'd put on my own Jeep.