Scion TC Won’t Turn Over

Hey everyone, I’ve been having the problem of not getting my Scion to start. It’s a 2005 AT. I’ve went through the basic checks to figure out what it was.

After realizing it wouldn’t turn over even with a jumper, I first thought it was the Starter Relay. I tested this theory by putting a safety pin into two of the terminals. Once I did that, the vehicle would turn over and start. I then went to replace that part and it did not fix the issue. Still wouldn’t turn over.

I proceeded to get input from multiple other websites and actual mechanics. They all told me different things at this point. Most said the Neutral Safety Switch. Some said the starter solenoid. One said the starter itself.

I decided to change the Neutral Safety Switch. I did and it didn’t make an impact. Still didn’t turn over. I then bypassed the starter relay with the Neutral Safety Switch to see if it would turn over and it did. That left me right where I began.

Next I decided to change the Starter Solenoid itself. I kept my old starter moter. After doing this and reinstalling the starter the same result happened. The car did not turn over. If I bypassed the starter relay it would.

Lastly I decided maybe the starter itself had gone bad. I bought an entirely new starter that came with its own solenoid preattached. It did not fix the problem. Car wouldn’t turn over. I went to bypass the relay again to check and it would start with a jump.

The only remaining mechanism of the starter system I’m aware of for this vehicle is the ignition switch. Could this be the problem? I’m not sure if it would make sense because of where it is in the wire diagram. Also bypassing the starter relay shouldn’t start the car if the ignition switch itself is bad, right?

This leaves me to wonder what else could posssibly be wrong? My only guess at this point is I may have been given a faulty starter relay in the first place from Auto Zone. What are your thoughts? Is that possible/common? Is there any other issue I may be missing?

I appreciate any and all help you can give me.

Thanks!

Because you jumped the relay and it worked, you now know that the secondary circuit is good. You now need to determine what’s wrong with the primary circuit. If you are sure the nuetral safety switch is good, it’s going to be the ignition switch at the start position, or bad wiring from switch to relay. You seem to have a diagram, so look what else can stop voltage from getting to the primary side of the relay. Don’t forget ground. Pins 1 and 2 are primary on your relay with 2 being ground.

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Yes indeedy… There was no need to continue anywhere near the starter or its solenoid after bridging the terminals at the relay as you proved that out already.

See if you can probe the relay socket to see if your ignition key is energizing one of the terminals at the start position… Er…what am I doing… Hows about you just follow the excellent advice offered by @tcmichnorth … he makes excellent points

Thanks this was very informative! I went ahead and changed the ignition switch out. Still had the same problem (doesn’t crank, starts when bypassing the relay). Every aspect of the starter system is now brand new (minus wiring). Does that leave wiring as the problem? I don’t fully understand how that would be the case. If when bypassing the relay I can turn the key and start the car wouldn’t the wiring have to be good throughout? Could it simply be the relay (fuse) replacement I got was bad? Let me know your thoughts, I appreciate the help!

Check your battery cables, both ends and cable itself. Look for corrosion and swelling

The starter motor won’t be able to spin the engine if the input voltage to it isn’t at least 10.5 volts. Jumping around the starter relay may be reducing the resistance enough to increase the voltage at the starter motor 9 volts to 10.5 volts. That could explain the symptoms. Suggest to measure the voltage at both input terminals to the starter motor (B and S). With the key in “start”, both should measure at least 10.5 volts, measuring from each terminal to starter case. Do they? One you have that data you’ll have something to work w/ here for help w/ a diagnosis. Doing that measurement is much easier than replacing any of the stuff you’ve replaced.

Okay, I do have corrosion on them. I could replace those. I’m curious (if you could help me better understand) why would the relay being bypassed make the key turn over the car and start (when it doesn’t turn over with the relay in)? Thanks so much!

Start with the basics and work your way up. Maybe the relay is bad, some mysteries have yet to be explained.

Anything is possible you could have a bad new relay, but not probable. Remove your starter relay and put your red voltmeter lead in pin 1 from the car. Put your black voltmeter lead on the battery negative post. Look at your diagram and confirm that this is the right pin to be testing because I’m just a stranger who found a diagram on the internet. Have someone turn the key to the crank position. You should be reading full battery voltage. Have them hold it there as long as you like while observing the voltage. If there’s no voltage or not enough voltage there is obstruction in your wiring or some componant between your ignition switch and your power distribution center. Try this in nuetral also. If you have voltage then, it may be the safety nuetral switch. If you have battery voltage on pin 1, then put your red meter lead in pin 2 and black lead to negative battery post. Have someone turn the key to crank position and hold it there. If you see over .3 volts you have a bad ground. I know we don’t like to here it’s a wiring problem but it happens all the time. @Barkydog brings up the very first thing that should be done though. I mistakenly thought that would have been done already.

Here’s the circuit

Battery +12 volts ------- Relay ---- starter motor S terminal.

The current to the starter motor S terminal is 20 amps or so. A resistance of 1/10 ohm anywhere in the circuit would reduce the voltage at the starter motor from 12 volts to 12 - 20* 1/10 = 10 volts.

Voltage in volts = current in amps * resistance in ohms

Bypassing the relay likely reduces the circuit’s total resistance.

Great this helps a ton! Thanks to all of you for your input and help. I’ll take these steps next and let you know what happens (also may help someone else in the future)!

You need to check for power and ground on the control side of the starter relay. Power on the control side of the starter relay comes from the ignition switch, passes through a 7.5 amp fuse and the park/neutral switch, then to the relay.

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