1995/96 LS400 instrument cluster repair.

Howplum · February 23, 2021

I don't seem to be getting anywhere finding a replacement cluster so am investigating replacement of the relevant electrolytic capacitors, which I assume are the the cause of he misbehaving fuel and temperature gauges. I've read about there being three capacitors which can cause issues, the third being for the panel lights (which work just fine).

Anyway, I was a bit surprised to find that there are 12 capacitors in total with very little commonality between them. On visual inspection they all look fine, but that probably means nothing.

I have done a sketch of the capacitors and their details and wonder if someone would be kind enough to tell me which ones I should be ordering.

I'm not sure my soldering skills are up to replacing the very small ones, so the next step is finding someone to test/replace the suspects.

Any help would be greatly appreciated.

Howplum · February 24, 2021

Whilst there is nothing obviously wrong on the side with the larger components on it, the other side is a different story, which is no doubt a result of the historic damp issues. All of the solder joints are suffering from surface corrosion, which hopefully will clean off with contact cleaner. However, in the following picture the corrosion on the solder joint to the left of C126, which is the positive connection to capacitor C132 on the other side, appears to be spreading, potentially onto part of the circuit it shouldn't.

Here's another picture showing corrosion on the many smaller components:

It looks like I need to be busy with the contact cleaner, fibreglass pencil and magnifying glass. Who knows, I might get lucky.

Howplum · February 24, 2021

Well, cleaning up the rear of the PCB made it look better, but unfortunately didn't cure the problems, so I now throw myself at the mercy of any electronic experts who might be reading this.

I did speak to BBA-Reman this morning, who said a repair would cost in the region of £175, which I'm a bit reluctant to shell out for at the moment.

ColinBarber · February 24, 2021

What is the problem you are experiencing with the gauges? How are they misbehaving?

Howplum · February 24, 2021

The fuel gauge always shows empty with the low fuel warning light showing on the first start of the day, although on a subsequent starts it usually shows the correct level, with no warning light. However, I did notice last year that on a longish journey the needle would slowly drag itself to the correct position, but that could take anywhere between 30 minutes to an hour.

The temperature gauge only ever moves a few millimetres from it rest position, not even reaching the lowest mark. However, I did dismantle the entire cluster last year in an attempt to sort out some non-functioning lights (which @steve2006 kindly sorted out for me in the end), but I wonder if I accidentally damaged the gauge in some way.

All other functions of the cluster work normally so it makes sense to repair my existing unit rather than try and source a used one, which might have its own issues. At least swapping the odometer is simple enough.

Any advice you can offer would be appreciated.

steve2006 · February 26, 2021

Easiest way to determine if it’s the cluster or sender unit is to remove the connection to the sender on the tank and ground it...this should produce a full tank indication on the cluster. If it doesn’t you either have a broken wire between the sender and cluster or a faulty cluster.

BigBoomer · February 26, 2021

Not impressed with their electronics maker. Any such circuit should have been sprayed with a conformal coating AFTER the circuit was soldered and that pretty obviously hasn't or there would be no corrosion on those contacts. Mind you it's been good enough for 20+ years and Lexus really don't care after 10 years.

You can reflow those solder joints with a soldering iron, but you need to be aware of what you are reflowing and what effect the heat of the soldering iron might have. Electrolytic capacitors do not always look visually damaged when they die and the only real way to test them is to remove them and use a capacitance meter on them.

As Steve said, I would eliminate all other possible causes, and once certain the problem is in the instruments, send them off to be done by a pro.
Messing with electronics you can sometimes cause more damage than you fix, especially if there are CMOS integrated circuits in there as they are very sensitive.

Howplum · February 26, 2021

Thank you Steve and George for your replies.

As far as the fuel gauge is concerned I am assuming, possibly incorrectly, that the sender is OK since the it works fine once the car has been running for a little while, even just on a local trip to the shop. Nevertheless, I will test it as suggested.

On the other hand, the temperature gauge is consistently misreading, so it might well be that the sender is faulty. I see from the wiring diagram there are two wires, brown and red/blue. I have just watched a video testing a sensor in situ with a multimeter which looks straightforward enough.

In layman's terms, what is the function of an electrolytic capacitor?

Do faulty capacitors tend to give consistent symptoms?

I do have a spare cluster, albeit from a 1997 model, but perhaps the gauges themselves could be swapped, if other tests prove inconclusive.

Howplum · February 26, 2021

I'm assuming the coolant sensor, of which there appears to be only one, sends a signal to the instrument cluster, either separately or via the ECU. As far as I am aware I have no running issues, which seems to be a symptom of a failing sensor.

ambermarine · February 27, 2021

16 hours ago, Howplum said:

I'm assuming the coolant sensor, of which there appears to be only one, sends a signal to the instrument cluster, either separately or via the ECU. As far as I am aware I have no running issues, which seems to be a symptom of a failing sensor.

16 hours ago, Howplum said:

Thank you Steve and George for your replies.

As far as the fuel gauge is concerned I am assuming, possibly incorrectly, that the sender is OK since the it works fine once the car has been running for a little while, even just on a local trip to the shop. Nevertheless, I will test it as suggested.

On the other hand, the temperature gauge is consistently misreading, so it might well be that the sender is faulty. I see from the wiring diagram there are two wires, brown and red/blue. I have just watched a video testing a sensor in situ with a multimeter which looks straightforward enough.

In layman's terms, what is the function of an electrolytic capacitor?

Do faulty capacitors tend to give consistent symptoms?

I do have a spare cluster, albeit from a 1997 model, but perhaps the gauges themselves could be swapped, if other tests prove inconclusive.

A capacitor is basically a reservoir of power that enables a constant supply through surge and drain episodes it is also used for shunting components such as electric motors that are induction motors which need a power boost to start rotating.

If a capacitor is failing symptoms that you are describing do occur but are not limited to a faulty capacitor.

Malc · February 27, 2021

I find all this electronic mullarkey starting to go awry so so frustrating ......... we have fabulous cars, comfy, powerful and purring like a pussycat and we can relatively easily achieve component continuation .. e.g UCAs etc ................... BUT the quarter century old electronics seem to be not quite so well at " holding up " and very tricky to resolve

Can't for one moment imagine that a quarter century young new, modern EV will be any better tho ................. and probably just simply a throwaway :wink3:

Malc

Howplum · February 27, 2021

1 hour ago, Malc said:

BUT the quarter century old electronics seem to be not quite so well at " holding up " and very tricky to resolve

I suspect almost any car over a certain age will have electrical gremlins, which is why forums such as this, and enthusiasts in general, help keep our cars on the road, despite the lack of support from most manufacturers.

At least Lexus didn't use bio-degradable wiring for the engine harness, which is what Mercedes-Benz did in the 1990s.

Howplum · March 1, 2021

I haven't been able to do any component testing yet, but did make some enquiries about having the cluster professionally rebuilt, and of those that replied BBA-Reman were the most competitive at £170, with a "Lifetime" guarantee.

I have also been trying to track down a used replacement and Jap Parts have one is stock, tested, for £300, so if push comes to shove I'll know which one to choose.

Boosh. · March 1, 2021

I have no personal experience of BBA-Reman, and I really like the idea that a company is repairing the parts that they cover. But do be aware that their reviews (on Trustpilot) seem very polarised. Happy customers are less likely to post in to a survey than happy ones, of course, so these surveys can give a false impression. Perhaps people on here have had good experiences?

This is them, isn't it? :https://uk.trustpilot.com/review/shop.bba-reman.com

Howplum · March 1, 2021

I have used BBA-Reman before, when they rebuilt the throttle body of my W124 Mercedes, and am perfectly happy with their work.

BigBoomer · March 2, 2021

Electrolytic capacitors can fail in 3 ways. Either of 1 or 2 can normally be fixed by replacing the capacitor.

1- The usual broken contact either internally or where they are soldered to the board.
Sometimes when they warm up, they start working as the heat expansion "fixes" the broken contact.

2- Loss of electrolyte. Results in reduced effectiveness so can give intermittent results.
This is your "blown" capacitor. Typically they have either squirted goo or have a swollen appearance.

3- Internal short circuit (rare!). A capacitor is basically just 2 metal plates separated by an electrolyte.
If the plates touch at any point, they become a piece of wire.
Normally damages other parts of the circuit but rare in Electrolytic capacitors.

If I were you, I'd go with BBA-Reman but first you need to check those sensors. :thumbsup:

Howplum · March 3, 2021

Yesterday I dismantled the both the spare (incorrect) cluster and the original so that I could swap over the fuel and temperature gauges, which are the same on both clusters.

I had limited success, in that I had indeed accidentally damaged the temperature gauge needle when I dismantled the original cluster before, so installing the replacement restored that function. The damaged part is the very delicate coiled copper wire on the upper part of the spindle, above the plastic disc:

Unfortunately the fuel gauge still registers empty on starting from cold, but performs normally once things have warmed up a bit, so I deduced that:

1. The fuel gauge itself is OK (unless both are faulty!)

2. The fault probably lies in the PCB, or a component thereon, as mentioned by @BigBoomer

Thank you all for your replies, but for the time being I will live with the issue. In the meantime, if anyone is interested in seeing a cluster in a dismantled state here are a few pictures:

cruisermark · March 3, 2021

I also found these guys aswell:

Lexus LS400 instrument cluster Speedo (91 on). - Cluster Repairs UK

Howplum · July 9, 2021

My cluster issues rumble on. I have sent the unit to both BBA-Reman and ECU Testing, both of whom sent they couldn't test it because they apparently didn't have the correct jig. All the other companies I found weren't interested, even though Cluster Repairs UK had a page on their website specifically for the LS400.

However, I have found a small company in Aylesbury who, when I rang, didn't say no when I asked if he liked a challenge, so I have sent him some pictures, since when I've heard nothing. However, I shall contact him again next week, hopefully armed with more information. I have a wiring diagram, so have established which three wires are from the fuel tank sender, and which pins they go to in the large grey multipin connector. Tracing their path on the PCB is a job for an expert though. I have found repair kits (3 electrolytic capacitors) for earlier models in the USA, but no mention of post 1995 models, which I assume must be different, and probably more complicated. Does anyone happen to know which of the 12 electrolytic capacitors relate to the fuel gauge? See my post on February 23rd.

The temperature gauge was riding over the stop, so the needle was starting from a lower point than it should, but having stared at it and prodded it gently it seems OK now, at least off the car.

Regarding the "sticking" speedometer and tachometer needles, there seems to be no stop for the needles, which must be inside the sealed unit. However, I did read on one US repairer's website, taninautoelectronix.com, the following:

"Please Note: Because these clusters don’t have a needle stopper from the factory for the mph and rpm, we add that on our repairs and rebuilds. This prevents the needle from sticking and makes the life of the motor longer but in order to do that, we put the needle stopper a little higher than 0 mph/rpm. This makes the needle show it’s on 1mph-2mph when the cluster is off/car is stationary."

This makes sense, and at least I have a spare cluster to experiment on.

Howplum · July 9, 2021

I should add that my attempts to track down a used unit have so far been unsuccessful, mostly because the relevant sellers on eBay don't have the common courtesy to reply.

steve2006 · July 9, 2021

Have you tried these guys Howard, I actually went for a job interview there but the pay was crap!

https://www.ecutesting.com/?gclid=EAIaIQobChMIm_W-_dPW8QIV0-3tCh0OVAuGEAAYASAAEgLbZfD_BwE

Howplum · July 9, 2021

Steve, that was one of the companies that said they couldn't test it. As I've discovered, there seem to be quite a few versions of the cluster over the years.

ambermarine · July 10, 2021

It seems the popularity of the LS400 is defeating your attempt to find a replacement cluster there are more people chasing this car than ever and those who own one are hanging on to them and not scrapping them.

The breakers yards are your best bet both here and in the states it is unlikely the electronic refurb guys will be interested because a complex jig costs money and there would be little work for it knowing the reputation for Lexus reliability .

The corrosion issue will be a major factor and difficult to determine as it can be shorting out circuits that are not showing corrosion. The intermittent fault you describe were the power builds up over time is a corrosion issue as it as the characteristics of a blocked pipe in practice.

The instrument cluster on the Lexus LS 400 as changed several times cosmetically over its production period but the dials are still fundamentally the same ,would it not be possible to adapt the circuit board from a 97 model just for the dials ,may need a bit of fettling but I think it is feasible.

steve2006 · July 10, 2021

Sorry Howard didn’t notice that you had already tried that company, regarding capacitor failure the only one I can see from your pictures that is possibly defective is the largest one situation to the top right of the orange socket, guessing here but maybe 470uf 25V. If you compare it to the others the plastic sleeving has shrunk exposing the top fully indicative of overheating and increased ESR.

Howplum · July 10, 2021

Phil, you are right about the gauges themselves being interchangeable, at least between the 1996 and 1997 versions, because did swap the temperature gauges over.

I take your point about the effects of corrosion, but at some point last year Steve did very kindly sort out the lights, and removed a lot of the corrosion in the process, so hopefully it will no longer be a factor, but who can say for sure?

As far as the speedometer and tachometer gauges are concerned I have no idea whether those on the 1997 unit have the same sticking issue, so instead opted to install stops, as mentioned on the US website I found. This is the result:

Hopefully they will do the trick. Obviously they will give a slightly higher reading on both gauges, but probably not enough to worry about in the real world.

Which just leaves the fuel gauge. Steve, to my untrained eye the electronic capacitors look fine, but obviously you have a great deal of experience in electronics so you could well be correct. The large one above the orange connector is indeed 470uf 25v, and the two even larger ones to the right of the yellow component are 820uf 25v, if that's relevant. Perhaps one option is to ask an electronics engineer to replace all 12 ECs and be done with it.

Hopefully I'll get there!