james250

My ISF has a P0500 Speed Sensor circuit error and from what i've read it may be the Revolution sensor on the transmission itself. Looking at diagrams in the parts catalogue, it appears there are two revolution sensors on the transmission as pictured below. Does anyone know if both of these are related to the speed sensor circuit? Are they both removable externally from the transmission or does the transmission have to be taken apart to get to these sensors? Any help would be much appreciated. Thanks

lobuxracer

iTrader: (2)

You are confused about how this system works. From the FSM:So you have a problem with the signal either from the skid control ECU, the Combination Meter, or the ECM. I have been able to empirically determine only the rear wheels are involved in the speed signal generation despite the manual showing inputs from all four wheels. If you put the car on stands and put the gearbox in drive, you get a proper speed indication even though the front wheels are not moving.

james250

so are you saying that the speed sensors in the diagram in originally posted has nothing to do with P0500 error code? What will be best way to diagnose this?

the cluster has Speed signal pin 5 (+S) and pin 17 (Si) is this a signal sent to the cluster itself? So technically could I plug in a oscilloscope across on pin 5 and pin 16 while driving and see if there is a pulse voltage?

lobuxracer

iTrader: (2)

Not saying they have nothing to do with it. It's possible they're malfunctioning, but there are a whole line of devices between the wheel speed sensor and the ECM that could also be the root of your problem. It's unlikely (but not impossible) that both rear wheel speed sensors have failed. Many mechanics have not followed the instructions for replacing the rear hubs and damaged the wheel speed sensors in the rear. But the code you are getting implies the signal from the skid control ECU is not getting where it needs to go.

Long answer short - yes, you can check those pins for a waveform. If it is not present, the skid control ECU and its wiring are suspect. If you have Techstream, you can read each of the wheel speed sensors feeding into the skid control ECU and save a lot of troubleshooting time, but yes, an o'scope at the combination meter connections will also tell you if there is a signal from the skid control ECU.

james250

thank you for this. I believe the car had been involved in a rear end collision in its life and you mentioned that mechanics often don’t follow the correct procedure to replace the rear hubs and damage the wheel speed sensors. I’m leaning towards this theory as the speed sensors of the transmission are towards the front of the car and the car was involved in rear collision. Do you have any tips on how to inspect the wheel speed sensors? And what the part numbers for them are? Is it a DIY job to change them? Is there a way to possibly test the wheel speed sensors?

I had a brief look at a is250 tech doc for that error code as I had accsss to that document and on that Lexus didn’t point to anything about the sensors on the wheel hub which I’m assuming is the abs speed sensors right? I would have thought the isf and 250/350 will all have abs sensors on the wheels no?

finally? Where is the skid control ECU located?

thank you so much for your help

lobuxracer

iTrader: (2)

Lexus doesn't call them ABS sensors, they call them wheel speed sensors which is more accurate as a description because they are used for a whole lot more than ABS. The skid control ECU is located beneath the HVAC blower motor on early models, but got moved in 2011. I don't have access to RHD manuals, only US and Canada, so that may not be exactly correct.

The wheel speed sensors, LH 89546-30070, RH 89545-30070, are not difficult to replace or test if you have Techstream. Techstream will show the inputs and outputs of the skid control ECU, so if the sensors are not working, you'll see it immediately with Techstream. Replacing them is pretty simple, basically one bolt holding them in place. Just disconnect the connector, remove the bolt, remove the old sensor, and install the new sensor, bolt it in (8.5 Nm) and connect the connector, you're done. Without Techstream, you can hook up a 'scope to the sensor output and see the waveform to determine if the sensor is working correctly, but it's a whole lot better if you use Techstream because it validates the signal is strong enough. First test if this fails is checking the wiring since the car has been involved in a rear collision. It's very possible the wiring is damaged and it's not worth spending a pile of cash on parts when the wiring isn't good. Here's the wiring for the US and Canada. Hopefully this helps:

jimhudgins

I posted in gs 350 thread, but your advice got me looking.I found something unusual ,but you put me on track. not as easy as trans speed sensor. Mine did involve a wreck with a sloppy mechanic.