Few vehicles have a reputation for reliability like the Toyota 4Runner. That is why one owner’s 2019 4Runner, with only 24,000 miles, became such a frustrating case. It kept dying at random, and he no longer trusted it enough to drive it.
The truck ended up with a Toyota and Lexus specialist who posts as @TheCarCareNut. He walked through the whole saga, from a simple dead battery to a fix he says he had never seen in his career.
How A Dead Battery Turned Into A Mystery
The 4Runner was a low-mileage weekend vehicle, so the battery went flat. During the jump start, the cables went on backwards. On a Toyota, he says, that usually just blows the main fuse.
Next, the owner called a friend who repairs semi trucks. According to the mechanic, that friend found the 140-amp main fuse blown, replaced it, and also said the alternator had failed, so he swapped that too. The next day, though, the truck would not start reliably and began shutting off on its own.
After that, a check engine light showed a crank position sensor code. So the owner took it to a Toyota dealership, which replaced the sensor. The very next day, the 4Runner died while reversing. When he brought it back, the dealer drove it and found nothing wrong.
The Tap That Shut The 4Runner Off
At the specialist’s shop, the owner said it had died four times while backing into the parking lot. Even so, the mechanic could not make it fail. He drove it several miles, restarted it again and again, and found no trouble codes.
Rather than send it home, he took the owner for a ride. The owner explained that it usually happened at slow speeds while parking. Together, they parked the truck about 17 times without a single stall.
Finally, he asked about the earlier fuse repair. Since that was the only unusual work, he opened the hood and tapped the fuse block. The engine shut off immediately. When he lifted the block, it started. When he let go, it died again.
Four Loose Pins On The Starter Relay
He took the fuse block apart, expecting a broken wire. Instead, he found nothing obviously damaged. Then he discovered the real problem.
“Four loose pins on the starter relay.”
That surprised him, because a starter relay normally does nothing once the engine is running. However, he explains that on this push-button 4Runner, a power management computer controls the starter relay. It also watches that circuit for a ground signal. If the connection flickers, the computer loses track and can shut the engine off. With a bad connection, it may also refuse to start.
“I’ve never in my entire automotive career thought if you pull a starter relay, the car will act up.”
As for the cause, he believes someone spread the pins while testing the circuit with a large tool during the first diagnosis. He calls it, to a point, an innocent mistake. He also says the dealership could hardly drive the truck for days waiting for a random stall.
What 4Runner Owners Can Take From This
The lesson reaches beyond one Toyota. Here is our take on it:
- Double-check cable colors before any jump start. Reversed cables can start a long chain of repairs.
- Write down exactly when an intermittent problem happens, such as speed, gear or temperature.
- Offer to ride along with the technician. Your description can point them to the cause.
- Ask what parts the last shop touched. New problems often start where someone last worked.
- Keep the old parts and receipts so the next shop can see what changed.
Where Things Stand
After tightening the relay pins, he ran a final test while his helper shook the harness, and the 4Runner stayed running.
“You have witnessed the needle in a haystack and this car is fixed.”
The plan now is simple. The owner will drive it for a couple of months to rebuild trust. Afterward, the shop plans to replace the aftermarket alternator from the first repair with a genuine Toyota part.
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