txshan130

Hi All -

Have a 2004 RX330 displaying a P0500 code along with associated Trac Off and VSC lights. No other codes besides the P0500.

Have done a fair amount of troubleshooting to include replacing the transmission speed sensors (before I found the repair manual), checking the combination meter speed input and output signals, and checking the ECM speed input signal. So here's what I have...

- All 4 ABS speed sensors are correctly showing speed on the OBDII display with car in motion
- Speedometer, Odometer and Tachometer all work normally (according to manual, speed sensor is operating normally if speedometer works)
- Transmission shifts just fine
- Combination Meter ECU Speed Signal Input (C9-18) correctly displays a good waveform with car in motion
- Combination Meter ECU Speed Signal Output (C8-6) incorrectly shows a constant 4.7 volts and does not fluctuate with car in motion
- ECM SPD Voltage (E6-17) also incorrectly shows a constant 4.7 volts and does not fluctuate with car in motion

So from what I gather, the speed sensors are correctly sending their signals to the Skid Control ECU which is correctly converting the signal into 4-pulse signal to the Combination Meter ECU. At this point, the same signal should be outputted to the ECM but for some reason, it is coming out of the Combination Meter as a constant 4.7V signal...

Any ideas on what I can try next besides just replacing the whole Combination Meter? That's the whole instrument display and is roughly $1000 to replace :-(

There are a few capacitors (no visible sign of leakage) on the Combination Meter ECU board...Has anybody had to replace them before?

Thx in advance for any help....pulling my hair out trying to solve this!

Nad1370

It will be close to impossible for you to see voltage fluctuation when driving at speed using a multi meter. (im assuming thats what you are using to check voltage)
For a proper check. you have to jack up the vehicle and turn wheel "slowly" to see the voltage change from 4.5-5.5v to 0v.
Neutral, Key ON posistion.
P0500 code is usually a bogus code that just shows up for no reason.
Unless its coming on on you often, just blow the code and see if it returns on the next trip.

txshan130

Actually I did just that...put it on jacks and slowly turned the wheel. Still just a constant voltage signal.

mnewxcv

Does vehicle speed show correctly Via obdii? Also, is the signal supposed to pulse with just one wheel turning? Or are you completely off the ground and 'driving' the wheels?

txshan130

Both front wheels were turning while on the jacks ... Vehicle speed shows zero via OBDII but I think that comes from the ECM (which is why it is reporting the P0500 code) . Under the ABS section on the OBDII, each wheel shows the correct speed while in motion so no problems there. Also tried slowly rolling down the road while watching voltmeter also... Same results. I could plainly see the waveform on the input side to the combination meter while the output signal was a steady state constant voltage.

Thinking of buying an older replacement combination meter (ECU) of Ebay and giving it a shot. Not sure how one deals with the different odometer setting however. Can they be reprogrammed?

Nad1370

If I remember, speed sensor --> skid control ECU ---> speedo head ---> ECM.
Combo meter sends the pulse signal to the ECM.
If the ECM doesnt see the pulse from the combo meter, then the 500 code sets.
If you are getting straight 4.7v and no fluctuations while on jacks (4 wheels of the ground, key ON and in NEUTRAL ) and turning the wheel slowly, I'd have to agree with you on a bad combo meter.

By any chance, does your OBD scanner record freeze frame when the code trips?
If you blow the code, does it come back right away after driving?

I was also thinking maybe you can cheat the output signal from the combo meter.
Do this at your own discretion. Im washing my hands on this. Lol.
Splice a wire from C9-18 to the output C8-6.
Thats if you are also getting 4.7v fluctuations on the C9-18 wire. (you mentioned wave form here but not voltage)
You obviously have to cut the output wire C8-6 of the combo meter.
Doing this bypasses the combo meter.
Im just not sure if its the same 4 pulse signal.

txshan130

---------------> Going to recheck this tomorrow. I did it with 2 wheels off the ground and wheels were spinning a bit in neutral. I did have the voltmeter hooked up while driving very slowly also with the same flat 4.7V result so thinking my original test result was valid.

---------------> Yes, it does, but none of it means much to me. It shows vehicle speed as zero. I can grab a screenshot tomorrow.

-----------------> Yes, it comes right back


------------------> Great idea! I may do that in the end and see what happens. From the manual, it appears that the signals going into the combo meter and coming out of the combo meter should be the same (although for some reason I remember seeing a higher top end voltage on the input side of the combo meter vs on the output side of the combo meter). Will check that again tomorrow also.

txshan130

The pic below would seem to suggest that the above may not be possible...

mnewxcv

Trouble Code: P0500 (3.3L V6 VIN - Auto)
Vehicle Speed Sensor Circuit Malfunction

Number of Trips to Set Code: 2

Trouble Code Conditions:
Engine started, vehicle driven with the engine speed from 1500-5500 rpm and back to idle several times, and the PCM did not receive any VSS signals during the test. The VSS (No.1) assembly outputs a 4-pulse signal for every revolution of the rotor shaft, which is generated by the transmission output shaft via the driven gear.

Possible Causes:

• * VSS signal circuit is open between the meter and the PCM
  
• * VSS signal circuit shorted to ground between meter and PCM
  
• * VSS No. 1 is damaged or has failed
  
• * Combination Meter is damaged or has failed
  
• * PCM has failed
  

Nad1370

I was banking it would be the same 4 pulse signal.
But that would be too good to be true. lol
Just for kicks, check the voltage fluctuations on C9-18 anyways. For reference of course.
Well, i guess just back track your checks once more.
If you still come up with a constant 4.7v, combo meter time it is.

Nad1370

^^^
This is good stuff

1. He is reading a constant 4.7v at the E6-17 at the PCM. An open would have no readings at all
2. He would be reading "0v" if it was shorted to ground. He has 4.7v
3. He's got a working speedo hence speed sensors are working (no sensor code as well)
4. Our primary suspect. Should be 4.5-5.5v - 0v fluctuations. Currently putting out a constant 4.7v.
5. Going to rule this out for now since its not getting the correct pulse signal from the combo meter.

txshan130

So I just re-checked the E6-17 voltage. Just checked it while slowly driving down the road at maybe 2 mph, then faster. No fluctuations at all in the 4.7V signal. I'm assuming it makes no difference if the car is up on jacks or is going down the road (although the repair manual talks about checking it while up on jacks). Don't have an oscilloscope either so all I can do is check voltage signal.

From the 2 pictures below, I think we've confirmed different voltages of the speed signal going into and out of the combo meter...











Thanks for all the help so far by the way....it's very much appreciated!

Nad1370

^^^^
Hahaha..
This was actually a great diagnosis thread.
Instead of just throwing parts at it.
Hopefully that combo meter swap will rid that 500 code.
It all points to that anyways.

txshan130

Yup... Think we're down to a combo meter swap. So next question - how do you get the odometer of the replacement to match the current odometer reading? Do you have to take it in to the dealer? Any idea on cost? My RX330 only has 130k miles and all the replacements I can find have 180k plus miles. ..

txshan130

Well sort of answered my own question. Toyota dealer nearby said they would charge 1 hour of labor ($120) to reprogram odometer. Guess I can test it out first and see if it fixes the problem and gets rid of the P0500 code before taking it over :-)