No-Crank After Hot Road Trip - Shorted Starter Wire & Battery Failure

Electricaladvanced✓ OP Confirmed

Problem

After a 430-mile road trip in 100°F weather, the car would not crank at all. The Optima Red Top battery was visibly deformed (spiral cells expanded upward), and even after installing a known-good battery from another Supra, the car still would not crank - no click, no engagement, nothing. Dashboard would light up normally but starter would not engage.

Car will not crank at all - no clicking soundDashboard lights up normally when ignition turned onFuel pump runs when ignition is onOptima Red Top battery top deformed/bulging from heatCoolant reservoir above Full line after tripTemperature gauge reading higher than normal on uphill climbs40A FL AM1 fuse blown (J/B no. 2 next to battery)17 ohms measured between starter wire terminal 50 and engine ground (should be open circuit)

Root Cause

The extreme heat caused the Optima Red Top AGM battery to internally short and deform. This cascading failure also blew the 40A FL AM1 fuse (which protects starter relay, alternator, TCCS ECU, and headlight cleaning motor). Additionally, the starter wire between the starter relay and starter terminal 50 developed a short to ground somewhere along its run through the firewall, preventing the starter from receiving the crank signal even with a good battery and fuse.

Confidence

Moderate confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted June 2020 on SupraForums.com