A 2019 Toyota 4Runner with about 24,000 miles on the odometer spent weeks stalling at low speed, and the trouble began with a battery that was jumped backwards. The reversed connection blew the 140-amp main fuse. Replacing that fuse turned out to be the easy part of a repair saga that passed through a truck mechanic and a Toyota dealer before a specialist found a handful of loose pins in a starter relay.
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Autoblog news editor Yash Bajaj reported the case on Nov. 4, 2026, drawing on a video from The Car Care Nut, an independent Toyota and Lexus specialist whose host runs his own shop, TCCN Automotive, in Homer Glen, Illinois. The diagnosis is one shop’s account rather than a statement from Toyota, and Autoblog says so plainly. Even so, the sequence reads as a compact catalogue of how an intermittent electrical fault can send owners and technicians after the wrong parts for weeks at a time.
The 140-amp main fuse and the backwards jump-start
According to Autoblog’s write-up, the owner’s battery died and the SUV was jump-started with the cables connected the wrong way around. The Car Care Nut said that reversed hookup blew the 140-amp main fuse, which he described as the place where the damage usually stops on a Toyota. In other words, the first failure was cheap and well understood, and a new fuse would normally have closed the matter.
Cable order is where such mistakes start. Edmunds’ jump-start guide, written by senior consumer advice editor Ronald Montoya, sets out four steps: one red clamp on the dead battery’s positive terminal, the other red clamp on the booster battery’s positive terminal, one black clamp on the booster’s negative terminal, and the final black clamp on unpainted metal on the dead car’s engine, away from the battery. Start the booster car first, the guide says, and check the owner’s manual for the exact sequence.
Autoblog’s own video guide, presented by Larry Kosilla, adds that a wrong hookup can damage a car’s factory computer. Neither guide singles out reversed polarity by name. Motor1 has shown how easily the order goes wrong in practice, with a viral dealership clip from November 2025 in which a man connected jumper cables in the wrong sequence and a loud honking started as soon as the equipment was switched on.
An aftermarket alternator and a crank position sensor that did not cure it
Intermittent faults punish guesswork, and the 4Runner’s history shows how quickly the bills pile up when each visit ends with a plausible but unproven explanation. A blown fuse, a tired alternator and a sensor code are all believable culprits on an SUV that stalls and will not restart, which is why each one was acted on in turn.
The first shop to see the 4Runner was run by a semi-truck mechanic. He replaced the blown fuse, then found what he judged to be a bad alternator and fitted an aftermarket unit. The SUV kept dying and would not restart, so the alternator swap had not touched the real fault, and the owner was back to square one with a lighter wallet.
A Toyota dealer was next. A diagnostic code pointed toward the crank position sensor, and the dealer replaced it. The next day the 4Runner stalled again, this time while reversing, and the dealer could not reproduce the problem on its own premises. The Car Care Nut believes neither the alternator nor the sensor needed replacing, a judgment Autoblog relays as his opinion and not as a finding confirmed by Toyota or by the other two shops.
Four loose pins in the starter relay
The fix, once found, involved a relay rather than a fuel, ignition or charging component. Weeks of stalling traced back to a part the first two shops never examined.
The owner told the specialist the stalling happened only at low speed while parking. On a test drive the 4Runner ran perfectly, which is the usual trap with intermittent faults. The break came when The Car Care Nut tapped the fuse block under the hood and the engine shut off. Inspection showed a loose starter relay with four loose pins, the root cause he settled on.
His explanation is that the power management computer watches for a ground through the starter circuit. If that contact flickers, the engine can shut off or refuse to restart. He told viewers he reproduced the stall on another Toyota with a similar setup, which gives the theory some support. He also suspects someone had spread the relay pins open with a tool during earlier testing, though he presents that as a theory about how the pins came to be loose.
Two pieces of practical advice come out of the case. Owners chasing an intermittent problem should tell the shop exactly when it occurs and offer to ride along, an approach Autoblog credits with cracking this one. They can also ask what test showed a part had failed before agreeing to replace it. Open questions remain: Toyota has not commented, nobody has established who loosened the pins, and Autoblog links only to The Car Care Nut’s channel, not to a specific video, so the full diagnostic footage was not available to check.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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