EpixINC

okay done some searching, but found nothing exactly what i am looking for. I have a 92 SC400 and the speedo doesnt work at all. lights come on, tach works if i hit the dash once or twice, fuel and temp work fine. none of the needles light up. but the speedo doesnt move at all until i am up around 70 or 80 i think. found out that it might be my speed sensor. I am assuming it is mounted somewhere on the transmission and is synced with the STOCK wheel and tire size. can anyone tell me where i should look or post an undercar picture of where the speed sensor is located? that way i can check it out and so... also if anyone knows the resistance levels of this sensor, or a way to test the sensor to see if its the speedo or the sensor that is bad, that would be great. You know, can i like ground one of the wires running to the speedo or somethin to make the needle move all the way? u know like a coolant temp sensor....im used to the mechanical speedos, where u just hook the cable to a drill and spin it... then u know if the speedo is bad. someone please help. and if anyone has any working needles i would be interested in purchasing them off of you.

EpixINC

come on peopler someone must know where this speed sensor is!!!

TTSC3

Not sure if it's the same as SC300, but this was what mine was...
https://www.clublexus.com/forums/sho...d.php?t=314703

EpixINC

okay not what i am looking for,.... thanks though. actually im looking for the actual sender located either on the trans or the rear diff. its gotta be one of those two places... dont think they would install it on the actual wheel....

gadgetSC

You should have 2 speed sensors located on the tail section of the transmission. One on each side.



gadgetSC

EpixINC

okay thank you gadget.... is there a test procedure that can be done? like checking the resistance between two points or grounding one wire to make the needle max out.??? quick question... why are there TWO? one for reverse? or what?

gadgetSC

From a service manual....The #1 Speed Sensor outputs a 4-pulse signal for every revolution of the transmission output shaft. After this signal is converted into a more precise retangular wave form by the wave form shaping circuit inside the combination meter. It is then transmitted to the engine and ECT ECU.
To test you have to access the back of the combination meter(Plug C14 pin 14) Its the plug on the left if you are looking at the rear of the combination meter. You will measure between ground and pin 14.
The test procedure:
1. Shift the shift lever to N range.
2. Jack up the rear wheel on one side.
3. Release the parking brake fully.
4. Turn IG switch ON.

Measure the voltage between terminal SP1 of combination meter connector and body ground.
Voltage:
Constantly 5v - Check combination meter circuit.
Changes 0v - 5v Replace engine and ECT ECU

The #2 Speed Sensor goes directly to the ECU. The gear shift point and lockup timing are controlled by the ECU based on the signals from this speed sensor and the throttle position sensor signal.
If the #2 speed sensor malfunctions, the ECU uses input signals from the #1 speed sensor as a backup signal.

#2 sensor is a bit easier to check. You can remove it and check the resistance. Resistance should be 560 - 680 Ohms.
Hope this helps

gadgetSC

EpixINC

so does that mean the #1 sensor cannot go bad? if i am getting no voltage at the back of the cluster, then it says to replace the engine and ect ECU??? how do i determine if the #1 sensor is bad?? DAMN I NEED A FSM!!! #2 is gonna be easy thanks.

bain

EpixINC,
What else have you found? I haven't even determined if the speedometer/odometer is driven by Speed Sensor 1, Speed Sensor 2, or if there is a separate speedometer speed sensor. My symptoms are speedo not reading (maybe 2 or 3 mph on the highway), odo not reading much, and cruise not engaging. I get a clean bill of health when pulling the engine and transmission codes.

Can anyone help us out? Which sensor drives the speedometer? Is there a diagram anywhere?

Thanks for any help.

EpixINC

okay well my odo works fine, the cruise works fine, but the speedo doesnt move except on the highway like urs Bain, just like 10mph at the most when im doing like 70.... so my guess is it is probably the speedo in the cluster is bad.

bain

I've seen some posts around on this topic where the circuit ground between boards in the dash are bad, and posts on capacitors going bad. The ground problems stem from using attachment screws between board to pass the signal ground. One posted solution was to GENTLY tighten said screws. Another added wire along the screw to help complete the circuit. Randomly replacing capacitors could be simple enough for the solder-savy, but more damage than good could also be done.

Maybe this weekend I'll pull and replace Sensor 1 (it seems like this drives the speedo) and maybe look at the plastic gear (I haven't even crawled under there yet!!). I'll try to post what I find.

EpixINC

did u ever find anything? which wire do i use?