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About 6 weeks ago, my 2005 Sable wouldn't crank. The dashlights and headlights worked, but the starter wouldn't engage. I had it towed to a mechanic who diagnosed a bad starter. That seemed to correct the issue until last week when after driving the car and parking it for a few minutes, it wouldn't crank again. I'm in another town so I had it towed it to another shop thinking the new starter may be bad. The mechanic can engage the starter and crank it with a button that connects to the solenoid and battery. The ignition won't energize the starter relay. He says the neutral safety switch is good and thinks that the theft deterrent system is the problem. I have three keys, two are OE keys and one is after market. I've used all three previously with no problems. None of them work now. The theft light comes on when the ignition is turned to crank, but goes out after a few seconds. This mechanic doesn't have whatever is needed to program or diagnose the theft deterrent system. He has checked for broken wires in the steering columns. I just wondered if anyone has any ideas about how to troubleshoot further. Thanks in advance.

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Hi! Welcome! Sorry to hear, when the theft system light comes on, does theft light come on for 3-5 seconds solid then shut off? Also, when the mechanic cranked the engine with the tool to the solenoid, did the engine start? If so I would rule that system out. 

Neutral safety switch unless testing the component could be a viable solution. AaorqjU.png

The way this system works is when the key is rotated to start, the 15 amp fuse (Fuse 21 under the driver side interior) will energize, test for 12 Volts on both sides of the fuse as there's small metal tabs you can probe with a multimeter, if this energizes when key is moved to Start, the ignition switch is good, if not - bad ignition switch most likely, or if you have any aftermarket remote start system or anti-theft system, that can cause problems. From there, Fuse 21 feeds the transmission range sensor, and that requires car to be in  P or N during the key in the start position. If that switch is good, current will flow to the battery junction box and power will apply at pin 85 of the starter relay, there will be 11-13 Volts DC with key being held into the start position at this relay terminal; if there is no power at pin 85 of the relay, there's either: 1. Bad Neutral Safety switch, or bad wire. If good, then If anti-theft fails, the other side of the relay (Pin 86) will not ground, thus the relay won't flow current to engage the starter. Simple way to test? Put key in ignition and should ground with key on/engine off, pull starter relay, test for ground between relay pin 86 and ground. Should have close no resistance. If that passes, anti-theft is not your problem.  Then, the 40 amp fuse that is hot at all times will connect the starter solenoid to 12 Volts when the relay closes, thus engaging the starter circuit. 

There is a lot in diagnosing a no-start condition, but this wiring diagram will help isolate the issue. If I had to guess... I'd say either bad ignition switch (verifiable by testing fuse 21 under dash to see if you get 12 volts on both sides of fuse) or a bad neutral safety switch (verifiable by ensuring 11-13 volts flows to pin 85 of starter relay). If Anti-Theft is defective, you'll need a new PCM since that is what provides the ground for the starter relay to engage which I highly doubt is the issue. 

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As you stated above, the theft light comes on for a few seconds, then goes out when switch is on. The car will crank when the mechanic connects his starter button to the solenoid and battery. He tested the neutral switch with something, I don't know what. I know he said that the readout would show each gear shifter position as it was moved. Because of that, he thought the neutral switch was ok. I'm going to send this info to him and see if he may be able to go further with it. Thanks for your help.

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The fuse 21 was blown. I replaced it and the car cranks. I really appreciate your help.

 

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Great! Glad to hear it :) 

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After thinking about this, in your opinion, what would be the most likely cause for the fuse blowing? I'll keep some in the car now in case it happens again. When I had the starter replaced in April, the mechanic said that the old one was shorted. The car acted the same. It was driven during the day and parked until 10pm. When attempting to crank it, the lights came on and the starter wouldn't engage. It makes me wonder if the mechanic may have replaced the starter, then the fuse afterwards. I guess I'll know if the fuse blows again. 

Again, thanks for your input.

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2 hours ago, tgm said:

After thinking about this, in your opinion, what would be the most likely cause for the fuse blowing? I'll keep some in the car now in case it happens again. When I had the starter replaced in April, the mechanic said that the old one was shorted. The car acted the same. It was driven during the day and parked until 10pm. When attempting to crank it, the lights came on and the starter wouldn't engage. It makes me wonder if the mechanic may have replaced the starter, then the fuse afterwards. I guess I'll know if the fuse blows again. 

Again, thanks for your input.

That fuse must feed something else beside what is on that diag. No need for 15A and it only feeds a relay coil. Likely something on the same fuse.

-chart-

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Based on power distribution, I only see that fuse feeding the Transmission Range sensor/Starter circuit. That's why if the fuse is blowing, I'd be wondering if there is an internal short or high resistance through the trans/neutral switch sensor. 

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I replaced the fuse last weekend and started it several times over the weekend. My son drove it back to his house the next morning, about an hours drive. The next morning, it wouldn't crank and the the fuse was blown again. It blew a few more times after that also, but after driving short distances. Maybe, this will make it a little easier to pinpoint the problem. He left it with the mechanic that replaced the starter in April.

 

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