Hello All,

I had a cel come on for the 2nd time in the past couple of months. Both times it is throwing a P0456(small leak in evap system). The other was a "C" code that said the voltage regulator was either using too much or too little voltage. I had autozone do a test and it was determined that it was around 13.5v or so.I tried tightening the gas cap as I saw this was pretty common among scion tc owners. However, I again have both codes being thrown out from the cel. I was wondering if anyone else has had these problems and what they did to fix them.

Thanks!

 

The gas cap thing is pretty common. In my case, it would work its way loose in a day or two. I tried a new oem cap, and that only lasted a year before the same things happened. I then bought an replacement cap from Stant, and that one fit infinitely better than the oem one. Been good ever since.

The other code may be a failing regulator for the alternator. You should check the voltage with the car off (~12V), with the engine running (13-14V) and at a high idle of 2500 rpm (should be around 14.6 or so). You could try replacing the alternator, but I hate throwing parts at a problem until you diagnose it. If it's over-voltage, then change it out asap as it could fry the electronics.

 

Forgot to add, also all the connections to and from the alternator and battery. Make sure they are tight and that the harness is secured and clean. Always do the easy stuff first.

 

Thanks. I appreciate the input. Do you know whether the voltage regulator is built-in to the alternator, or is it separate? I heard from clubsciontc, i believe, that it is separate.

 

X2 with everything bbsciontc has said. I also got tired of the oem caps failing and bought aftermarket (stant). haven't had another problem with the cap and it does fit much better than the oem's ever did! The oem's felt loose even when new!

also I agree with the alternator, check the voltage while it's running..

 

The voltage regulator is built into the alternator. It's a small unit on the side of the alternator casing (inside the case). Whoever told you that it's separate over at CSTC doesn't have a tC, because you can see it if you look under the hood at the alternator! It's not uncommon (not unheard of) that the alternator dies on the tC, usually it's around 100k miles when they finally give up. Denso is the original supplier of the alternator, I think they did a good job, nothing will last forever and at least we can count on 100k trouble free miles until it "gives up".

But.. I had an original Honda alternator go (rebuilding a civic) and replaced it with a TYC (new, not rebuilt like many are out there in the aftermarket) and it has been excellent! Put's out more amps than the stock alternator, always a plus! And it wasn't expensive, about $120, where Honda wanted.. yes I have to go off topic and say this (made me laugh so hard I almost fell over) that Honda wanted $1250 for a new alternator! hahaha.. even the dealership began laughing. wow Honda is officially insane!!

So you could go with a TYC it should work well for you, is what I was saying A new tyc alternator at rockauto for the tC is $189. Just letting ya know!

 

Scion xB 2015. The voltage regulator is apparently under a black cover on the side of the alternator. There are two connectors: one is apparently the thick wire for charging output. The other has multiple small wires. It is necessary to remove these two cables in order to remove the black cover. My question: how may I disconnect these?