LS400 electrical gremlin

[JayBeeBee]

Not doing to well with lexus... my LS430 is playing up with a misfire and now my 1998 LS400 has decided to play up too... I have an issue where the temp gauge momentarily drops right down to nothing, at same time the gearbox selector light on dash goes out and the revs drop. when I go to get out of the car and turn lights off, they stay on momentarily then go out but the light warning on dash stays on and goes out after a while. when this is happening, if I lock car with fob, it will not open with it again and I have to use key which means alarm goes off... really am getting to wits end with Lexus grrrr :(

[cruisermark]

Starts with checking and replacing battery 

[JayBeeBee]

Battery went completely flat thru lack of use and when checked said replace so i did have a new one fitted :(

[MotorDevil]

Would it be worth restting the ECU to see if that clears anything?

Could be a bad ground maybe too? 

[Tulpen]

13 hours ago, JayBeeBee said:

getting to wits end with Lexus grrrr 😞

Now, there's a first...……...the rest of us all think 'Lexus grrreat!'   😀

[ROYT]

Try a different Battery, I've had new batteries that are faulty

and always buy brand quality.

Also as previously suggested check all earths, [or grounds if you prefer]

and Battery terminals are clean and tight

[JayBeeBee]

Sooo tried different Battery and earth from Battery good... Is there another earth to check? Ive noticed also that when I switch lights off, the warning lamp in dash seems to stay of for a while... could I possibly be looking at a dash issue? wouldn't have thought that would cause Battery to drain over couple of days though?

[John N]

Yes there is another earth to check.

I had an intermittent misfire on a Lancia Thema I ran for a few years, which turned out to be the earth connection between the engine block and the chassis. It is just as important as the earth from the Battery to the chassis. 

If you are getting misfires, use a diagnostic tester to read the fault codes. If all the misfires are from the same cylinder, it will probably be a fault with that cylinder, eg. spark plug, ht coil or fuel injector. If the misfires are coming from all the cylinders at random it will be an electrical fault like a bad earth.

John N

[Herbie]

On 2/18/2020 at 6:21 PM, JayBeeBee said:

wouldn't have thought that would cause battery to drain over couple of days though

Your original post didn't mention that this was happening.

It sounds like you have a parasitic drain somewhere so you need to do some logical and methodical fault finding with the correct tools.

At the very least you'll need a multimeter and a clamp ammeter would be a big help too.

You need to establish (maybe from workshop manual or a spec sheet) what quiescent current draw is normal for your car. A general 'rule of thumb' is that around 36mA is considered to be normal, with some cars drawing up to 50mA still classed as acceptable, but much more than that would usually be indicative of a fault.

There are a few videos on Youtube about finding a parasitic drain and this is a fairly good one:

 

 

[JayBeeBee]

Thanks. I shall try that. Where I been using my 430 I left the 400 and the Battery had died so replaced Battery as test showed Battery no good so then I replaced it and went out a couple of days later and found the new Battery was dead again... Luckily I have a back up car to use :)

 

[messi]

Sounds like the alternator to me 

[Herbie]

1 hour ago, messi said:

Sounds like the alternator to me 

Yes, good point.

I just assumed he would have checked that first, along with having the Battery replaced.