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oil light on but oil pressure ok and oil pressure sensor replaced

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Old 04-04-13, 06:07 PM   #1
lexaus
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Default oil light on but oil pressure ok and oil pressure sensor replaced

Hi All thanks for all the fabulous info on this forum.
On my 1995 LS400 the oil pressure warning light was coming on intermittently and is now on all the time. I have checked the oil level and had the oil changed, which I do religiously every 5000kms.
I also had the blown bulb warning light on constantly even though all bulbs were OK. I took it to an auto electrician who fixed the bulb warning light but told me to get the oil pressure checked before he looked at the oil light.
I was positive it was the sensor because it was leaking oil so I replaced it but the light stayed on.
Panic! Have I blown up the motor by running it for a few days with low/no oil pressure?
I bought an electric oil pressure gauge and the oil pressure was fine - 80psi @ idle when cold, 20psi @ idle when warm, rising to 100psi as revs increase.
Phew!
So, I have a motor with 400,000km and a few oil leaks but good oil pressure.
The oil pressure light (red) is on constantly.
The oil level light (orange) is working correctly. ie it only comes on when oil level falls below approx half way mark on dip stick (which it never does in normal circumstances).
That leads me to believe it must be an electrical fault. There is only one wire to the sensor and I measured 12v at the connection to the oil pressure sensor.
How does the oil pressure warning circuit work?
Is the sensor open circuit when there is no oil pressure?
If so when the oil pressure build up does it close the circuit and how does that turn out the warning light?
I don't know what the auto electrician did to fix the bulb warning light. He may have disconnected or bypassed something. Could that have any impact on the oil pressure circuit?

One final question not related to the main topic. The oil pressure gauge I bought has already paid for itself 10 times over with the peace of mind it bought me but now I have it I'm thinking I might as well install it permanently. Has anyone installed an oil pressure gauge in their LS400? Where did you put it? Did you run it in conjunction with the existing oil pressure light? I'm assuming I can get a T piece to screw in above the oil filter and connect the gauge sensor and the oil light sensor to that. Are there any other oil outlets I can use? I saw a couple of things that looked like switches or sensors screwed into the engine but wasn't sure what they were. I've also seen a glowshift oil filter sandwich plate
http://www.glowshiftdirect.com/oilfi...5thread-1.aspx
but they only list availability for the lexus is300 model
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Old 04-04-13, 06:44 PM   #2
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to clarify, you replaced the oil level sender, or the pressure sender?
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Old 04-04-13, 10:25 PM   #3
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Quote:
How does the oil pressure warning circuit work?
have you considered snagging the factory electrical wiring diagram and the factory service manual set on ebay? - it's a great investment!

or at least spend $15 and get a 2 day membership to the factory Toyota Information Center, and then at least you can learn how the oil pressure sensor is wired and how it functions.
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Old 04-05-13, 05:54 AM   #4
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Originally Posted by PureDrifter View Post
to clarify, you replaced the oil level sender, or the pressure sender?
I replaced the oil pressure sender. Is it safe to earth the 12v line to the oil pressure sender? I considered doing this to confirm that the oil pressure circuit was working but didn't want to short out anything
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Old 04-05-13, 06:54 AM   #5
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Originally Posted by LScowboyLS View Post
have you considered snagging the factory electrical wiring diagram and the factory service manual set on ebay? - it's a great investment!
Thanks for the suggestion.
I checked ebay Australia and found
"LEXUS LS400 V8 1995-2000 FACTORY SERVICE REPAIR MANUAL" on CD for $15.90
I've had mixed success with these sort of manuals for previous cars, but they usually cover enough details for jobs I would be prepared to tackle.

I found the genuine manuals on ebay USA, $39 for wiring diagram and $180 - $250 for 2 book set. I assume these are the manuals you were referring to. I would have to get them posted to Australia.

I also checked out the Toyota Information Center, that looked really good.

I'm guessing any of the options above would solve my immediate needs for info about the oil pressure warning circuit so I just have to decide whether to spend the extra cash for future reference. I'm getting a bit lazy in my old age and the car is so reliable I may never need it!! The oil pressure light and bulb warning light are the only things outside of scheduled maintenance that I've had to do in 40,000kms of driving.
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Old 04-05-13, 07:12 AM   #6
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Quote:
Originally Posted by lexaus View Post
I replaced the oil pressure sender. Is it safe to earth the 12v line to the oil pressure sender? I considered doing this to confirm that the oil pressure circuit was working but didn't want to short out anything
I only have a Japanese manual for 94-00 JDM Celsior.
I believe that the oil pressure sensing and the indication are the same with LS400. Below is from my manual. I added English names to the related area with red characters. I also added the red line for you to know which line is the oil pressure line. The line is not connected to the ECU. It is just an old style circuit. Bypassing the switch does not cause any problem, you can see by this diagram. Hope this helps.
Click the image to open in full size.
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Old 04-06-13, 05:13 AM   #7
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I only have a Japanese manual for 94-00 JDM Celsior.
I believe that the oil pressure sensing and the indication are the same with LS400.
Thanks Yamae. that diagram is very helpful. One thing that still does not make sense for me is that if I disconnect the wire to the oil pressure switch the oil light stays on. How can that be? If there is a wiring fault the current through the bulb might be earthed before the switch but then there wouldn't be 12v at the switch.

Based on the diagram I would have thought it was safe to try grounding the wire to the switch but because my symptoms don't match the diagram I still haven't been game to try it.

I checked the wiring diagram for oil lights for a few different makes of cars and they all seem very similar to the diagram you posted.

Any ideas?
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Old 04-06-13, 09:30 AM   #8
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Hi, Yamae-san.
Do you think it would be safe for him to ground the lead through a light bulb (to limit curent)?
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Old 04-06-13, 06:40 PM   #9
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Originally Posted by Gene01 View Post
Hi, Yamae-san.
Do you think it would be safe for him to ground the lead through a light bulb (to limit curent)?
As long as the circuit is the same with JDM's, it is quite safe to ground the lead since the current is limited by the bulb.

What I worry about is that the oil light is on without grounding and also the blown bulb warning light is on constantly even though all bulbs are OK. Something must be messed up but without observing and analyzing the actual unit, it is hard to tell more for me.
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Old 04-07-13, 08:03 AM   #10
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Lexaus, I've had a problem with the oil pressure warning coming on intermittently and it was caused by faulty oil filter. I replaced it with a different one and the warning went away. I will only be using OEM filters from now on.
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Old 04-29-13, 12:03 AM   #11
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Question problem found but not fixed yet

Hi All, thanks for all the help so far.
A few more questions for the gurus.
I replaced the oil filter and the oil pressure sender. No change.
I wired the oil pressure sender to a bulb connected directly to the battery and it worked as expected. The bulb was on, as soon as I started the car the bulb went out. The indicator light on the dash was still on even though I had disconnected the wire to the oil pressure sender.
I gave up and took it to an auto electrician who diagnosed it as an instrument panel problem.
Where to from here?
Repair instrument panel? Can it be done? Is it worth doing? The oil pressure light is currently the only symptom of any problems with the instrument panel but maybe the whole thing is reaching its use by date?
New instrument panel? very pricey plus more money to set odometer
Second hand instrument panel? Still have to set odometer
Interim measure.
I really don't want to drive the car with the oil pressure light on even though I know the oil pressure is fine.
I'm going to wire up a temporary oil pressure light and connect it directly to the oil pressure sender and remove the oil pressure warning bulb from the instrument panel. I haven't found a suitable place to put the temporary oil pressure light. Any suggestion?
I also have an oil pressure gauge which I'd like to install. I'm struggling to mount that where it doesn't look like dog's bxxx. Any suggestions? I saw something on an SC400 forum with 2 gauges mounted on the A pillar that didn't look too bad. Has anyone mounted extra gauges on their LS400? if so where did you put them?
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Old 04-29-13, 03:39 AM   #12
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If the switch is replaced and working correctly then the wire going to it is being grounded somewhere.

If you disconnect that wire from the sensor the light should go off.

If it doesn't your problem is somewhere else.

My conclusion is based off the posted wiring diagram.
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Old 04-29-13, 04:59 PM   #13
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Quote:
Originally Posted by lexaus View Post
Hi All, thanks for all the help so far.
A few more questions for the gurus.
I replaced the oil filter and the oil pressure sender. No change.
I wired the oil pressure sender to a bulb connected directly to the battery and it worked as expected. The bulb was on, as soon as I started the car the bulb went out. The indicator light on the dash was still on even though I had disconnected the wire to the oil pressure sender.
I gave up and took it to an auto electrician who diagnosed it as an instrument panel problem.
Where to from here?
Repair instrument panel? Can it be done? Is it worth doing? The oil pressure light is currently the only symptom of any problems with the instrument panel but maybe the whole thing is reaching its use by date?
New instrument panel? very pricey plus more money to set odometer
Second hand instrument panel? Still have to set odometer
Interim measure.
I really don't want to drive the car with the oil pressure light on even though I know the oil pressure is fine.
I'm going to wire up a temporary oil pressure light and connect it directly to the oil pressure sender and remove the oil pressure warning bulb from the instrument panel. I haven't found a suitable place to put the temporary oil pressure light. Any suggestion?
I also have an oil pressure gauge which I'd like to install. I'm struggling to mount that where it doesn't look like dog's bxxx. Any suggestions? I saw something on an SC400 forum with 2 gauges mounted on the A pillar that didn't look too bad. Has anyone mounted extra gauges on their LS400? if so where did you put them?
Now I understand that the lower side of the lamp is grounded always. There would be some points where the grounding might be occurred. Those would be,
1, inside of the cluster board,
2, the pin "12" of the connector "B",
3, the cable between above to the junction pint "8" of "DG1",
4, the wire above to the oil pressure switch.

If those are not related to other circuits, you just can add another oil pressure checking method and don't worry about the original circuits nor to replace the whole cluster unit that cost you some extra money.

To investigate more and to feel ease doing so, I suggest you to check the voltage at the oil pressure switch at least. Is it fully grounded and the voltage is 0V?

If there is some remaining voltage or unstable low voltage there, it would be the semi-grounding. In other words, the connection to the ground is not fully done. One of the points I wrote above 1-4 is barely causing a short circuit to the ground.

Other items you'd better to pay attentions are other unusual indications at the panel or some unusual behaviors of the car caused by the cluster or some others.

If you have any problem understanding my limited English, ask me again. I think I am good at circuits but not English.
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Old 05-06-13, 07:07 AM   #14
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Originally Posted by Yamae View Post
There would be some points where the grounding might be occurred.
Thanks Yamae, I'll check those 4 options out.
I have another more immediate problem which I need to attend to first. I hit a wombat (Australian marsupial) at 110km/hour so my car will be at the panel beaters for about a week. I'll get back to you in a week or 2
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Old 05-06-14, 03:43 AM   #15
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LSC or Yamae,

Would either of you very knowledgeable gents know how the LS400 Oil Level Sender works? I took one apart and it has two leads that are connected to what looks like a simple float type mechanism. However, this float does not have any connections at all! The float itself is free-floating on an insulated plastic pivot and seems to be some sort of very soft carbon material that covers a brass peg. The float appears to be able to slide up and down its pivot and another thicker brass peg as the oil level rises and falls. However, the peculiar thing is that both ends of the float have semicircular grooves sort of like an open-end wrench/spanner, and both the pivots seem to have something soldered within them, as evidenced by wire ends in the solder!? I don't think these are as simple at all, as some poster has stated where he said that the float makes contact at the bottom and completes a circuit when oil level is low. Also, these senders are around $400.00 (US), which makes me think there is more to it than that.

I ran a simple test with a DVM and slid the float up and down and noticed that the resistance varies!!!??? Any light you can shed will help me resolve my oil level light flickering on and off intermittently.

TIA

Last edited by fsuguy; 05-06-14 at 03:47 AM..
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Old 05-06-14, 03:43 AM
 
 
 
 
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