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Under the Hood: Neutral safety switch could be causing car's startup issues

Brad Bergholdt, Tribune News Service on

Published in Automotive News

Q: I'm having trouble starting my 2000 Toyota Avalon. It makes no sounds as I turn the key. I'm wondering if it might have a parasitic drain. It does start sometimes if I fiddle with the gearshift lever. Do you have any ideas that could help?

-- Ray H., Windsor, Calif.

A: It sounds like you may already be well on the road to diagnosing the cause, as you've noted there seems to be a change in symptom as you move the shifter. You made no mention of a dead battery or needing to jump-start the car, so a small continuous drain on the battery (parasitic drain) isn't likely.

To really nail down this problem, try this: The next time the Avalon fails to crank, continue holding the key in the crank position while you jiggle the shift lever. If it abruptly starts, or at least makes noises like it's trying, this is a solid indicator your neutral safety switch is failing.

The Avalon's neutral safety switch, also called a park-neutral position switch or transmission range sensor, is a triangular metal gadget attached to the transmission (left side, under-hood, visible) that works in conjunction with the shift mechanism. This rather easily replaced part (also requires adjustment) unfortunately comes with a list price of over $600! Sorry, I should have suggested sitting down first! Checking around, it's not hard to find an aftermarket replacement for about $200 to $300.

With such a high price, an electrical confirmation, taken via a couple simple measurements at terminals 1 and 3 of the starter relay, wouldn't be overkill, if a check could be made during a no-crank episode. This part is located in the under-hood fuse box. If the Avalon were to start or not start regardless of gearshift position, this would also be a productive place to diagnose the starter-request circuit, possibly indicating a faulty relay or starter. I tell my students relays are like a train station: Everything you'd like to see comes and goes from this location.

Q: When is it really time for new tires? My tire and lube place is bugging me to replace them, but my brother, a mechanic, looks at them and says maybe next spring! They're all wearing smoothly. They just don't look new to me.

-- Kelly R.

A: The legal and practical minimum tread thickness for tires is 2/32 of an inch. In wet weather or more demanding driving conditions I wouldn't go less than 4/32. And in snow, let's make it 6/32. You should see wear bars beginning to fill in the tread grooves as the tread approaches 2/32 remaining. Inserting a quarter into several of the tread grooves with Washington's head down is a good check for 4/32 remaining. If the top of his head is still obscured, you're OK, with more than 4/32 remaining.

Maintaining proper inflation pressure is vitally important. Some tire pressure monitoring systems are more accurate than others. A physical check of pressure once per month is a good idea.

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Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at bradbergholdt@gmail.com; he cannot make personal replies.

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