The anti theft system seems to be blocking the car from starting.

A little info about the car and the circumstances would help.....

2001 Altima. New battery and no engine problems.
Key won't activate the starter. There's clicking from a relay under the dash which causes the turn signal lights to flash ( like emergency flashers) for a minute or two.
I tried the Anti Theft Reset sequences found on Google and YouTube, none of those worked.
The right one might work.
The relay under the dash buzzes, the way relays in older cars used to buzz when they went bad.

Does it reset when you use the key cylinder in the door? Virtually all the theft systems in older Nissans arm and disarm using the cylinder switch. If it won't disarm, there's a good chance the switch is kaput. The switch on all the Alties until (I think) '06 was a separate part, not built into the lock/latch like on later models.

I followed one sequence I found online for using the key in the door to reset it, and it didn't work.
But I'm not sure if the sequence was correct.
Is there a reliable source for the exact order to use with the key in door lock? How long to hold it, etc?

Also, when I try to start it I hear the warning chime that tells us when we left the key in the ignition and opened the door, only I'm sitting in the car with the door closed.

It should reset just by cycling the key to the "unlock" position, nothing special needed. If that isn't working then a bad cylinder switch is a good bet.

I'm guessing it would be worth it to just replace that switch. I'd rather replace the whole system, one piece at a time, than get it towed.

Johnaltima600 wrote: ↑

Tue May 18, 2021 5:12 pm

I'm guessing it would be worth it to just replace that switch. I'd rather replace the whole system, one piece at a time, than get it towed.

The door panel isn't hard to remove, but the switches are pricey, $104 even from NissanPartsDeal. It's located on the back of the lock cylinder, so make sure you roll the window up before pulling the panel. Unless there's a short in the wiring, you can both diagnose and work around the switch by taking the connector loose, shorting the GRN/YEL wire to ground for a few seconds (that's the Unlock signal to the BCM), then leaving the switch disconnected. At that point, if the switch was the problem, the car should start. By leaving the connector loose the BCM will never see another Lock signal, so you'll have time to get a switch if you want the anti-theft to work again.

If that all doesn't do it, post back and I'll make some other suggestions.

I found a red/blue and a solid yellow wire leading towards the lock cylinder, but I can't figure out how to disconnect the plastic connector. Would the solid yellow one be the one to ground?

The colors on the switch side of the connector could be anything, so I can't say. But you should have a GRN/YEL, a LT GRN/RED, and a BLK on the car side of the connector. You can check the switch with a voltmeter (not a test light) with the connector in place, but to work around it you'll need to get it loose. With the switch still connected and the cylinder in the neutral position, you should see voltage (might be 5V or might be 12V) on both of the colored wires and 0V on black at all times. When the cylinder goes to Lock, the LT GRN/RED wire should go to 0V and the GRN/YEL should stay at voltage. When it goes to Unlock, the GRN/YEL should go to 0V and the LT GRN/RED should stay at voltage. If you see all of those things then the switch is healthy and we're barking up the wrong tree.

If the connector is just stuck, try dousing it with some WD40 or PB Blaster. Old connectors often get crud underneath the locking pawl and it makes them very stubborn to split.

I'm sure there's a licking pawl, I just can't figure out how to squeeze it to get the fitting to release. Now that it's daylight again, I'll get back to it.

There are two wires, no three..
A yellow, and a red/ blue.
No black wire.

Can't be the right connector, then. Nissan cylinder switches always have 3, Lock, Unlock and ground.

It appears that there are two wires, and the switch is grounded by a screw to the steel of the door, which itself is grounded to the chassis.

I dunno, that diagram came straight from the '01 ESM in the Nissan dbase, not a secondary source. So if it doesn't match, your guess is as good as mine.