Ls400 Won't Start Battery Is Fully Charged

[Jerry Martinez]

I have an 96 LS400 the battery indicator light comes on when I push on the brake , I drive it for a while and it starts to bogs down and stops, it cranks but won't start, I have it towed home and remove the battery to charge it up and the next day it starts like nothing ever happened, except the battery light comes on.

The car died again after a trip to the store I checked the battery and it has 12.2v it cranks but it won't start. Is this the ecu telling me to get the low battery indicator problem taken care of? If so when I repair the battery indicator will this problem stop.

[landar]

If you pull the battery and charge it on an external charger then reinstall, of course it will act like nothing happened...except for that pesky battery light. The reason is that the battery is 'happy' and fully charged. The car will chug along for some time before the battery is again drained. You root cause is the charging system on the car, most likely the alternator has failed or the serpentine belt fell off. I would charge the battery and drive it to an auto store which can check the charging system. Or if you have a voltmeter, measure the charging voltage with the engine running. It should be around 13.5 vdc(or so). If not, you replace the alternator or pull it and have it checked as a first step. Welcome, Jerry!

[Jerry Martinez]

No, I have the battery condition and it will go dead eventually, that I know, but it dies two different ways: 1) The battery goes dead nothing no crank, I read low voltage on my dvm. or 2) this is different, after I drive it for a while-- keep it revved and avoid the battery indicator mostly it is still charged all of a sudden-- it chugs and dies won't start but it still cranks. I disconnect the battery overnight the next morning it runs as if nothing happened! Is this the ecu becoming confused from the low battery or does this car have a fail safe telling me to get the charging system fixed and stop driving it?

[nook702]

I would agree with landar, another option is to take the battery to have it load tested. Could be a defective battery or intermittent alternator.

[Jerry Martinez]

I get the charging system part.

• New battery (got one)
  
• Checked voltage (13 v while running) may not be enough.
  

What my question is, I know it has a battery indicator light on. I know what it does when it is not fully charged (on't crank). What my car does is that, but also something new, after a while of driving with my battery fully charged (12.2v) it dies and won't fire (Not won't crank) won't fire! Remember the battery is fully charged and the engine is cranking, no fire. I disconnect the battery at night and the next day it starts right up no problems, like nothing ever was wrong.

• Question with my charging system sub-standard could my ecu become corrupted or does it have a fail-safe mode to prevent me from causing further damage and shut down my car?
  

[landar]

Ok. Now that is a little more and different information. If the engine is cranking then your battery is strong and charged and there should be enough power for the engine to fire. Only it does not run. But overnight, it mysteriously heals itself. Could be a bad electrical connection somewhere or a sensor (like cam/crank sensor) acting up. I wonder if it only refuses to start when the engine is hot?

Your question about the charging system being sub-standard and a fail-safe mode...no, I do not believe the system is being shut down due to any charge issue condition. Your alternator could have a shorted diode that is allowing AC (Alternating Current) onto the system but that is pure speculation at this point and probably not the case. And remember, the charging (or lack thereof) and the intermittent starting could be totally separate issues.

I would evaluate the charging system first. You have a DVM, so start the engine, turn the headlights on for a load and check the charging level. It should be north of 13.5v with RPMs at 2k. You should also test the voltage on the AC setting and note almost a zero reading. Also, do not rule out the battery and connections. Although you say the battery is new, it is not unheard of to get a defective "new" battery. Battery connections should also be rechecked to ensure that they are clean and tight.

[pj8708]

You may be showing a working charging system and a full battery, but something has to be draining the charge wether running or sitting. Have you checked for a short starting from the starter to the alternator, alternator fuse connector, etc. It could be the ECU but in my experience, as Landar implies, it's basic old fasioned plus meets minus.

Paul

[Jerry Martinez]

Alright! I checked the voltage at the battery with my engine revving at 2000 rpm and the headlights on for a load. 14v was my reading. The voltage at idle is around 13.2v. The battery is not getting drained but after 45 minutes of driving the car begins to sputter and dies. The battery voltage remains good 12.2v the starter turns the engine but it just won't start.

I disconnect the battery for about an hour and it starts like nothing is wrong, accept the battery indicator light is on. So what would cause it to die and after the battery is disconnected for an hour start like nothing ever happened?

[curiousB]

If you have 14VDC at the battery posts with the engine running and heavy electrical loads like the headlights on then you seem to have an OK charging system. Unless something is intermittent (like a loose connection on alternator charge wire, or battery) then it must be something else.

Maybe you have a phantom load (trunk, interior or glove box light on) that is leading to excessive "key off current" such that the battery is slowly being drained overnight. I installed a remote starter unit into a Ford and it caused a strange side effect where the vehicle ECU never dropped into low power sleep mode and drained the battery in 2-3 days.

[Jerry Martinez]

It looks like I have TWO 2 problems: 1) The car sputters and dies after 30-40 minutes of driving. Like it has no spark or no fuel. After the battery is disconnected for 30-60 minute or overnight it starts like nothing ever happened.

Problem 2) Battery light indicator comes on at idle and turns off at 2000 rpm and eventually after driving for a few days the battery might go low.

The question is: These items happened at the same time, are the related?

[curiousB]

Can you wire in some test wires right to the battery posts and then to your DVM inside the car. Then go for a ride and monitor battery voltage. With engine running it should always stay north of 13.3 VDC, at all RPMs.

If battery only gets >13.3VDC at >2000 RPM it could be worn brushes in alternator (something you can fix without replacing the Alternator, just a brush kit). Worn brushes would limit field current which can reduce output of alternator. It could be a bad regulator but since these are now all electronic you don't hear of them failing much.

[landar]

To me, this is beginning to sound like an intermittent cell within your battery... if you are correct in your voltage charge measurements. I know your battery is new but it is still suspect. It is not unheard of to have a new battery with a bad cell. Either that or a poor cable connection.The battery indicator coming on is a clear sign of either low charge voltage(which you ruled out), bad battery or poor connection. Do you have a known good battery from another vehicle that you could try?

Also, try measuring the charge voltage not at the battery posts but on the cable connector clamp heads with engine running and a load (like lights). There should be NO difference in reading between the actual post and clamp, else there is a bad/dirty connection.

[fsuguy]

Just a thought here ...

If while he is driving, the alternator is still providing enough voltage (>13.2V) and the engine begins missing - "...but after 45 minutes of driving the car begins to sputter and dies..." doesn't that rule out a battery problem?? The voltage from the alternator may not be enough to charge up the battery, but it should be enough to keep the engine running, and then the battery would not be charged up enough to turn over the engine!(?)

Sounds to me like a loose wire making intermittent contact and shorting out the fuel system somewhere.

[Jerry Martinez]

Update! Replaced the rectifier in the alternator and the battery, charges great no battery indicator on my dash.

Still have the problem were the car won't start after it has been driven for awhile but the very next day it runs fine.

[Jerry Martinez]

My Lexus LS400 started running rough and died, would not start, the very next day it started as if nothing was wrong. It does this scenario now all the time. It starts fine runs good for awhile then if you stop the engine it won't start until the next day...