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Gas Gauge Stays At Empty, No Low Fuel Light


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#1 BogeyJH

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Posted 18 March 2007 - 05:02 AM

Howdy from a newbie in Texas.

I just bought a 1994 LS400 Anniversary Edition. My first Lexus.

I bought it with a known problem with the gas gauge that seems to differ from the postings I foiund on the subject. The needle is always in the lowest fuel position and the low fuel indicator never lights.

I had thought this might be a float issue but thought that the fact that the low fuel indicator doesn't function might rule that out. I have also considered that this may be a connection problem.

However, there are quite a few references to the instrument cluster circuit board capacitors, which got me to thinking of the possibility that this could be related to other failures for which replacing the caps did the trick. The electronics are right up my alley as I am fairly handy iwth a soldering iron when I need to be, but I don't really want to risk going into the instrument cluster unecessarily since there are no other issues in that area.

Does anyone have any history on this failiure mechanism?

Any insights would be most welcome.

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#2 93ls400walt

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Posted 18 March 2007 - 06:39 AM

There are some threads that address this issue on the gas guage. In fact I had this prob. also. I bought a used cluster, as my tach and spedo, had issues too.

If I remember it is a cap. prob. that may be fixed with replacing them

#3 wandawoods

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Posted 18 March 2007 - 12:46 PM

well, gas gauge failure due to defective C142/C147 electrolytic capacitors on circuit board behind instrument cluster is very common on 1st gen LS400.

I fixed mine on the 94 LS400 I used to own few years back. instruction as below:
http://us.lexusowner...?showtopic=5822

#4 BogeyJH

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Posted 18 March 2007 - 01:47 PM

well, gas gauge failure due to defective C142/C147 electrolytic capacitors on circuit board behind instrument cluster is very common on 1st gen LS400.

I fixed mine on the 94 LS400 I used to own few years back. instruction as below:
http://us.lexusowner...?showtopic=5822

I saw your post during my search. I really appreciate the detail you included.

Is there any indication that the defective capacitors can cause the gauge to stick at empty and/or didable the low fuel indicator?

#5 wandawoods

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Posted 18 March 2007 - 07:19 PM

I saw your post during my search. I really appreciate the detail you included.

Is there any indication that the defective capacitors can cause the gauge to stick at empty and/or didable the low fuel indicator?

I recall mine was that the needle would rise only to 1/3 even tank was full. didnt pay attention to low-fuel light...

changing capacitors is very inexpensive, and relatively easy to do. was it me, I would do that first since we know very well that those capacitors are definitely going to fail over time, if not failed already.

#6 TexasLexus94

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Posted 19 March 2007 - 05:08 PM

My 94LS developed the dreaded fuel gauge problem. Nothing else was wrong with the instrument display-it just took too long to get to the correct amount. Living in a warm area, I figured I could live with it, since it is worse when the temperature is cold. However, after reading the excellent postings by the many experienced members of this community, who said the problems with the display would only get worse, I bit the bullet, and sent the cluster to Jim Walker, and the problem was solved. $225.00 incl shipping.

Funny thing is that it took me hours to remove, and later re-assemble the cluster. Bloody fingers and such....Thank God I didn't try to DIY the actual capacitor work. One post said it's 15 minutes out, and 15 minutes back in. Not for fumblefingers. But there are super instructions on this website, and it all went well in the end. Don't go to the dealer-your credit card will be maxed out....

#7 VBdenny

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Posted 19 March 2007 - 06:09 PM

It seems everything I do on the Lexus takes me quite a long time the first time but after that it, most things can be fairly easy. I recently saw a 94 or 95 LS400 in a junkyard and the instrument cluster was removed. I looked at what was in there. There was also one of the clock a/c culsters sitting on the back seat. I looked it over but didn't buy it since it looked pretty bad.

#8 BogeyJH

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Posted 20 March 2007 - 01:12 AM

I spoke with the previous owner of the car at lunch today (we work together at an RF engineering company). Turns out the gas gauge exhibited the common symptoms I read about in the forum (i.e. - indicating lower than full with a full tank) before it died altogether. He also said that for a couple of days after an unrelated service at the dealer, it worked normally. It then returned to the common failure mode for a while before eventually dying.

In addition to poor low temperature stability, one of the disadvantages of aluminum electrolytic capacitors is the finite capacitor life due to breakdown and degradation of the electrolyte. We theorized that the degraded electrolyte within the caps may have been temporarily restored to a functional state and then failed after encountering a succession of mechanical shocks or vibrations.

He had received an estimate to repair the gas gauge, but figured the cost was greater than the inconvenience. He is an excellent engineer and I commented that it is amusing to me that he makes his living designing, troubleshooting, and otherwise working with electronics but chose to live without a gas gauge and an intermittently blacked out climate control LCD when the fixes were well within his capabilities. He really dislikes working on cars, no matter the nature of the repair, so he never researched DIY repair of these minor problems. Otherwise, he was good about keeping up with the maintenance on the car, but always paid someone else to do it.

At any rate, this new information is encouraging to me in that the problem will very likely be solved with the replacement solid tantalum caps. I'm hoping the LCD on the climate control module is not too far gone to be corrected with new caps (it's only partially dark in cooler weather). johnls400 seemed to think that the LCD issue is cap related.

This weekend I'll download the instructions and tackle these two if I can squeeze in some time.

Many thanks to all of you for your input.

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