Help! P0500 Check Engine Code diagnosis

[Jeremy M.]

I just finished resurfacing my heads after they warped, basically a full head gasket job per the service manual I have, and after starting the engine, everything sounded and looked good until I put it in gear to go for a test drive. Once in gear, it didn't want to move and had very little power. I couldn't climb the slight incline back to my driveway, and had to get a family member to help tow the car back up.

I don't suspect that the head job was relevant, since none of the transmission connectors were even touched during the process, but I mention it in case it sparks some ideas.

Check engine light presents with the single code of "P0500- vehicle speed sensor malfunction". I pulled both speed sensors (located on driver's side of transmission, part no. 89411C) and tested them both to see what kind of output I could get from them. I'm looking for either a better test of the sensors, or a way to test the wiring (continuity test or resistance, etc.).

What I did to test the sensors was position them at about 20 thou from the chuck from my drill and spun the drill at it's top speed (an assumed 1800 rpm from specs, but I just thought I could get away with any speed as long as the process was repeatable). It isn't a completely accurate way of testing it, but since the three chuck prongs protrude from the center, as it spun I was able to get a consistent reading from both sensors of about 0.25 V AC.

I unfortunately can't afford to parts monkey the diagnosis and throw two new $60 parts at the car without knowing it'll solve the problem, especially after spending near a third of the car's value on a head job, so if anyone has any knowledge of how to test or diagnose this, I would greatly appreciate it.

Edited November 5, 2021 by Jeremy M.
Title change and clarification of the last paragraph

[Jeremy M.]

If anyone is able to add their two cents, it'd be appreciated- my latest theory is that the torque converter is starved for fluid, but I'm unfamiliar with the pumping system for the transmission fluid, so I don't know whether the torque converter will be filled with an idling engine. In my service manual, it shows the torque converter refilling by taking it out of the vehicle, but that's unfortunately not a possibility for me right now.

Does anyone have knowledge on whether a torque converter left sitting for 3-4 months without running would A. Drain it's fluid back into the transmission pan (there was no fluid leaks outside of the transmission) or B. Bleed out air in the system without me needing to remove the transmission and fill it manually?

[RX400h]

If the gas was sitting for 3-4 months then I would suspect it as the culprit.

[Jeremy M.]

I don't see the gas affecting it all that much if I'm honest- the engine does run, and revs fine. It just doesn't drive; the engine will rev all the way through the tach with no weird hesitations, but it refuses to give power to the wheels.

That being said, I'm definitely willing to try siphoning out the tank and filling it with some fresh stuff, since it can hardly hurt it.

If you're willing, would you mind explaining how rotten gas would affect the engine, just so I can try and match it up with my symptoms?

[paulo57509]

Please see attached.  These pages are from the 1998 FSM.

You will probably need an OBD-II scan tool (not just a code reader) that will report road speed.

DI-100 Engine - DTC P0500 - Vehicle Speed Sensor Malfunction.pdf

IN-30 How To Troubleshoot ECU Controled Systems - How to Use Diagnostic Chart and Proceedu.PDF

BE-99 Combination Meter - Inspection.pdf

[Jeremy M.]

Thank you very much- that troubleshooting chart in particular is just what I was looking for. My own service manual didn't seem to have the files for that section. I do have an OBD-II scanner with live data, so I'll go on through the process and check over everything.

[paulo57509]

You're very welcome.  Let me know if there's any other docs you might need.

[Jeremy M.]

On 11/19/2021 at 12:49 AM, paulo57509 said:

Please see attached.  These pages are from the 1998 FSM.

You will probably need an OBD-II scan tool (not just a code reader) that will report road speed.

Just wanted to hop back in and thank you again- I was finally able to get this today, and after double and triple-checking the resistances from that diagnostic section you shared, I found that one of the connectors was arcing because of a bent pin in the connector for the sensor, so the ECU freaked out, just like I did after I saw the code lol. It was a fairly quick (and free, thankfully) fix, just disassembling the connector and bending the pin sleeve closed a little bit. 

It was a load off my back, and finally the rear wheels are turning under their own power, at least while in the air. I'll likely wait until tomorrow to test it on the roads, but I doubt it would've been caught by me without the files you shared, so I can't thank you enough.

[paulo57509]

Jeremy, you're very welcome.  I'm glad you found your issue.

I don't know if you've heard of Toyota Information Service (TIS).  It's a subscription service; pay for a 2-day subscription and you have access to all Toyota documentation and everything is downloadable.  Drop $20 and have a download-fest for a few days.  You can manipulate the .pdf files (they're not password protected) if you have Acrobat

https://techinfo.snapon.com/TIS/Register.aspx

The subscription payment is handled by a third party (snap-on?) and the portal link is emailed to you.