Digital Speedometer fluctuating or displaying incorrect speed intermittently

[MS112]

Hello Toymods

My car is a 1990 era Toyota Crown, so built with the same technology as the Lexus LS400/Soarer UZZ30

The digital "Dual Vision" speedometer is exhibiting weirdness in the form of either

• Showing the wrong speed (e.g. higher than actual speed, if I am doing 20, speed is 40, 30 is 50 etc)
• Showing 180km/h (max speed)
• Showing 0km/h
• The speed readout been affected by braking once or twice. Feels like the change in voltage effects something somehow.
• Otherwise just fluctuating about

The occurrence is intermittent, and does not really appear to be triggered by bumps. Can suddenly happen on a perfectly flat road.

First thought was the Speed Sensor is failing. Oddly, the ECU does not think there is a problem with the Speed Sensor. I learned how to read diagnostics and the only stored code is 41 (Throttle Position Sensor).

Although on one occasion, when I first started the car and started driving and the vehicle speed stayed at 0, the "O/D Off" light started flashing. Still no code stored, however.

Has anyone else seen this issue before?

What I know so far

• Speed sensor input is fed to the instrument cluster first, before being passed to the ECU. (link)
• I suspected the Instrument cluster was at fault, but the Suspension and Central Locking respond to the changes in speed. However, it is unclear if the instrument cluster or the ECU controls those components.
• This thread was suggesting the ECU is the cause, however the speed signal is decoded by the instrument cluster first.

Thank you for your time

[RA35GT]

"O/D Off" light flashing happens when the auto ecu throws a code.
Did you put the diagnostic link onto the auto ecu pins? (not the engine ecu pins)

(Not sure if the auto ecu is separate or combined on those, but either way, they need different pins to be linked to go into diagnostics for the auto)

Sounds like a speed sensor issue to me...(either mechanically or electrically)

[MS112]

Hello RA35GT, I did try to read the diagnostic codes as if it were an LS400 - not much in the way of info on these import UZS131 Crowns - where it was said to read the Engine and Transmission codes, connect TE1 and E1 pins on the diagnostic port (Source)

Mind you, the Crown does have separate controllers for the engine and transmission in the UZS131, maybe I can't read ECT codes using this method. This thought had crossed my mind that it was separate procedure for the Crown, but I could not find any evidence otherwise.

[cresslux]

to read ect codes you need to bridge TT and ground. the tt pin may be different in an older model car, but when you enable it, this will flash error codes throught the OD light.

i *THINK* these have a seperate ecu for the transmission. i can confirm when i get home and have a look at mine.

[MS112]

Thanks cresslux, I can confirm that Crowns had separate ECU and ECT (see here under ECU). I will try that and see what happens

Recently, the speedometer started fluctuating and the car was not even moving. The plot thickens, so to speak. I am probably just going to have to bite the bullet and start inspecting the wiring.

[MS112]

OK, there was no TT pin (which I think is for checking TPS voltage?), there is an ECT pin but shunting that to E1 just lights up O/D OFF light.

[cresslux]

hmm interesting...

i know on older cars with and external ECT unit (such as a mk3 supra) the pin is called DG (on ECT unit itself) but in the diagnotic connector in the bay its called Tt (or sometimes just T)

if you sucessfully enable test mode, and there is no codes it will flash 2 times per second.

is the auto behaving funny? try unplugging the ect unit and going for a drive as to my understanding the signal should be speed senser>dash cluster>ect and see if it the cluster starts behaving normally (you will have to manual shift the auto L=1st, 2=3rd, D=O/D)

it also could be bad caps in the cluster itself.
hope this helps and good luck.

[rhys80]

Hi I know this is an old thread, but my 1991 toyota century is doing the same thing,

I was wondering whether you had any luck with finding out what it was?

Cheers

[MS112]

Wow you have a Toyota Century!

I am afraid I have bad news...The problem just went away

That said, the advice in this thread still applies.

Can you give an exact description of the sort of things the speedo is doing?

[rhys80]

Speedo intermittently works, O/D light flashes, speedo is either wildy inaccurate or displays 0 when moving, the "Super Monitor" says "Check ECT", there's another thread on here someone else on here had a VG40 Century had the same issue,.

[MS112]

Hello rhys80, my apologies for the month and a half follow-up reply, did you find a solution to your problem?

[ShanePedler]

Hi guys. I realise this is an old thread. I have a UZS131 running gear put into a Mazda B ute. Last night, I was getting the same symptoms as described above. Worth adding, is the problem seems to only occur after driving for 10 minutes. Also, the transmission reacts in accordance to the erratic speed display on the dash. So, if the speedo drops to 0km/h, the gear box will be stuck in first gear. If the speedo jumps to 180km/h, the gearbox will go up into forth gear. I replaced all the electrolytic capacitors in the ECT (and separate ECU) about 4 years ago so I doubt the problem is that. I'm thinking it's the electronic speedo drive or a connection thereabouts. I'll post an update when I get around to looking at it.

[alcyon]

Hi guys. I realise this is an old thread. I have a UZS131 running gear put into a Mazda B ute. Last night, I was getting the same symptoms as described above. Worth adding, is the problem seems to only occur after driving for 10 minutes. Also, the transmission reacts in accordance to the erratic speed display on the dash. So, if the speedo drops to 0km/h, the gear box will be stuck in first gear. If the speedo jumps to 180km/h, the gearbox will go up into forth gear. I replaced all the electrolytic capacitors in the ECT (and separate ECU) about 4 years ago so I doubt the problem is that. I'm thinking it's the electronic speedo drive or a connection thereabouts. I'll post an update when I get around to looking at it.

It is only the speed sensor. Take it apart, clean up all the green goo grease from inside with lighter fluid or electrical cleaning spray. Re solder the 3 wires on top of the hall sensor. Buy a tube of super lube (syncolon) synthetic grease , and regrease the shafts, as well as the spinning magnet. make sure you have plenty of this super lube grease in between the bushing and shaft. Put it all back together. make sure the geared shaft key sits properly inside the magnet shaft. Reconnect the 3 wire plug and drive it around. My problem came back after 15 mins on the very first test drive after the fix.. But, the very next day, I drove around for several hours and the problem did not come back even to this day. And that was like 24th December 2017.

[ShanePedler]

Thanks alcyon. Your solution worked. I even had the same once off issue in the first 15 minutes driving after reassembly but the problem went away. Done about 200km so far.

[alcyon]

Thanks alcyon. Your solution worked. I even had the same once off issue in the first 15 minutes driving after reassembly but the problem went away. Done about 200km so far.

Amen brotha. I believe the super lube grease helps with the magnetic field as its a good lubricating grease as well as die electric properties.