My IS350 has been having issues with starting over the past week. It first happened out of nowhere on a rainy day, where the car unlocked with my key fob just fine but it would not even start in accessory mode. The ignition button would not even light up with my key fob pressed directly against it. I replaced the battery in my key fob and the spare key fob and tried both individually, pressed against the ignition, but neither worked. I read online that this could be from a blown fuse, so in order to at least get my car started I switched the fuse #14 (10A "Ignition system") in the engine compartment driver side fusebox with the spare 10A fuse. My car started just fine afterwards, and I was able to get it home but it would not start again the next day. I checked the fuse I had switched out with a multi-meter and it was completely fine (i.e. not blown at all) so that was confusing on how it temporarily fixed the issue to replace it. I checked the glovebox fuse #8 (10A "SRS airbag system, cruise control, steering lock system, fuel system") and engine compartment passenger side fuse #4 (20A "IG2, IGN, GAUGE") and both were fine, and then tried starting my car again and it started just fine.

I tried to schedule an appointment but the soonest available for one of only two shops willing to work on an older Lexus (very few auto shops in my city) is two weeks from now., still awaiting a call back from the other shop This is clearly a very intermittent issue so I am apprehensive about bringing it in to a shop in the first place since they may not find anything wrong while my car is there. So a summary of what I've checked so far:

• Both key fobs have brand new batteries, both can unlock/lock doors and trunk
• Starter is less than 9 months old
• Car battery is less than 2 years old
  • Fully charged with NOCO Genius 10A charger
  • Reads 12.38V while off
  • Reads 14.03V while idling (which I read means the alternator is working properly?)
  • Tried disconnecting it for 5 minutes then reconnecting and car started fine... then didn't the next day
• OBD2 scanner showed no codes
• All "IGN" fuses are fine

My car started just fine again today, and has been starting fine all day every time I check it. This issue completely baffles me since it's so inconsistent.

I have read that one of the issues may be the fuel pressure sensor which tends to go bad eventually and prevent any starting, but is there a way to narrow it down to that specific issue? Are there any other steps I can take with a multi-meter without irreversibly damaging anything?

 

Was the car battery disconnected when checking voltage? So meaning it was a fresh ecu reset to say the least?

Usually after a battery disconnect the voltage will read 14+ V for a short time. Then settle down to mid 13V, or so.

If it's holding steady above 14V then maybe the alternator is over charging. Just something to look out for. Last to mention is check the battery if looks like it's bloated on the long sides.

 

12.38V while off is pretty low. Check it with doors closed, lights off 2 hours after shutdown. Then again in 2 hours. What does it read?

 

The battery was disconnected for over an hour (checked before and after charging with the NOCO battery smart charger, then after connected) so it reset the ECU. The voltage when idling was checked immediately after connecting and starting my car.

Should I leave my car off for a while, or leave it idling for a while in order to check that it is below 14V at idle?

The battery does not look deformed or bloated at all-- the long sides appear to be perfectly flat from my visual inspection after taking it out.

 

I will try to measure the battery again today, what is the ideal range? It seems like Optima says 12.6-12.8V, while J.D. Power says 12.2-12.6V, "go auto" says 12.6-12.8V ideal while 12.4V is acceptable, "batteriesplus" says 12.6V and "autobatteries.com" says 12.6V+.

Does that mean it should be a minimum of 12.6V for a healthy battery?

 

Let the car idle till the rpms settle down to normal. At that point check the DC V while it's idling. It should be around 13.2 - 13.8V. If any over 14V then then alternator is over charging at this point. Vice versa if you are reading below 12V then the alternator is failing to charge the battery correctly.

Like mentioned before a good battery in rested state will read 12.6V.

Say you measure that after car is shut off. Then come back 2 hrs later, and it measure 12.3 then you have a parasitic draw somewhere.

There are some good videos to watch on YouTube of this procedure.

 

My money is on alternator. I agree with MikeFig that it should be 13~13.8V, 14V max. Below that may give you the symptoms you are getting.

You can also check the cabling to the alternator to see if its rusty or loose.

 

Today marks the second day in a row with no start issues. I drove my car for a bit then checked it while off and it was at 12.54V.

I let it sit for a couple hours and it read 12.52V.

After turning it on and letting it idle for a few minutes it read 13.62V.

According to what I've read and watched, I feel like my battery is in pretty good condition and my alternator is working properly. Is there anything else I'd need to test to be sure?

 

Take a ride, turn on the a/c, radio, lights, then measure. It should continue to be 13.62~

If it goes down to 12.52 ~ then the alternator may not be working 100% or on its way out.

I was in the opposite situation, my regulator was going out so it would randomly go over 14v until it finally killed my battery because it went up to 17V onto my battery continuously. Had to replace my battery and my alternator.

 

It's at about 13.59V, so there doesn't seem to be an issue with the alternator as far as I can tell. This is extremely frustrating though because I feel like if I bring it in to a shop they'll say everything's fine and charge me for their time, then my car won't start at all the next day. Could a regulator going bad also prevent any startup?

 

What about the battery terminals, are they in good condition? is the ground in good condition (the part where it screws onto the chassis)?

 

It seems the battery just isn't holding charge. I'd take it to a local autoparts store to get tested. Just to rule out that possibility. If that checks out move to the next scenario, and start testing for a parasitic draw.

 

Please check the voltage again.
2 Hours after shut down. Leave the hood ajar if possible.
8 hours after shutdown.

Just try to be consistent with what doors are opened and all of that.
AGM batteries happily sit at 12.9V
Regular LA batteries 12.6 to 12.7V or 2.1/2.11 per cell.

But ya, I would be inspecting cables. When it does start, is it slow and labored or rather quick?

 

Have you checked the brake switch? If the car can't tell that you're pressing the brake it won't let you start it. Maybe its getting sticky or something.

 

for the fuel pressure sensor, i found this video helpful in diagnosing it.
i just went through its failure after having some starting issues similar to yours AFTER verifying my battery in my fob, battery in the car, and alternator were all working fine!