P0500 Code

I searched for an answer here before posting this but I couldn't find the answer I need.

I had the driver's side kick panel removed this morning. I have on-board air in my truck (2015 Tacoma) and behind said kick panel is a T-fitting that branches off from the main air tube and connects to an air pressure gauge in the dash. The T-fitting had sprung a leak.

After I got the T-fitting fixed I started my truck to air up the tank and WTF? None of my dashboard lights were working. The culprit turned out to be the 7.5 amp fuse behind the left-side coin tray. I replaced the fuse.

Then I fired up the truck again. All my dash lights are working now but the Check Engine light came on along with the Traction Control Off light. Double WTF.

I hooked up my ODB II scanner and it is showing a P0500 code which means "Vehicle Speed Sensor (VSS) Malfunction". Some online info says it can cause your speedometer to not work or your automatic transmission to not shift properly, but I made a quick test drive and the speedo and the tranny DO work just fine.

Then I thought I might have knocked a connection loose when I was dicking around behind the kick panel, but everything seems to be tight.

Any thoughts?

 

Perhaps just a bandaid but maybe have to reset the system. Could try undoing the negative connection on the battery for 5 min then doing cycle to let everything restart.

Had a similar problem with the pedal commandor. Had to undo it and reset for the lights to go away

 

So, if your speedometer appears to be working correctly that rules out the wheel sensors. It can only be one of 3 things: bad ECM, bad speedometer cluster, or the wiring between the cluster and the ECM.

 

Generally the vss is a sensor that measures revolutions at the trans or xfer case output shaft. With a constant gear ratio and tire diameter, this directly correlates to vehicle speed. Very few cars these days that don’t have one as I provides both speedo data as well as helps the trans module to confirm that a shift has taken place or if the TC is slipping ( it sees the engine rpm aswell). Wheel speed is the term for the revolutions of each wheel, as measured by the four wheel speed sensor. Mostly used for abs and traction control. Most cars use vss for speedo, but suspect some will use wheel speed as a backup source if the vss stops reporting. Not universal though. My bmw had a vss, but used the LR wheel speed sensor for speedo data. New to toyotas , so can’t speculate on what they do in their modules. Suggest the op check the vss, its wiring and connectors. Not a code you want to ignore, as it will eventually cause shifting problems or put the trans in limp home mode.

 

Did you drive it when your fuse was blown? If so that probably set the P0500 as the instrument cluster is responsible for providing the vehicle speed signal to the PCM.
https://www.tacomaworld.com/threads/2nd-gen-information-diagnostics.784008/#post-28042157

 

OK. Problem solved. And I guess it was indirectly kinda sorta my fault. Recap:

I took the truck to the dealership and they put it on their analyzer. They could see all the truck's computers except for the main ECU. After fiddling around some more they noticed that when they turned on the big lightbar above the windshield, the voltage to the computers dropped. Turn off the lightbar and the voltage when back up.

(Premature) Conclusion: All my accessories are causing the problem and I will need to disconnect them all. Sorry, not an acceptable solution.

Then my service advisor let me talk to the senior service advisor who was also their resident expert on electrical systems. He basically told me the same thing. I said OK, but before you give up can we try one last thing?

Now being trained in electronics and electrical systems, I installed all my accessories in a manner that they could be easily disconnected and reconnected for troubleshooting purposes. He let me go into the shop with him and I told them they only need to do two things to disable all the accessories: Flip the power switch on the relay buss bar, (which I did right there in front of them) and to disconnect all the cables from the positive secondary post on the battery. (I have a deep cycle battery designed for use in an RV that has the main terminal posts plus secondary posts to connect accessories).

So he disconnects all the accessories from the secondary positive post and runs the diagnostics again. Same. Problem. Well, that should rule out the accessories as being the issue. Then he looked under the driver's side dash and noticed something odd about the OBD-II connector.

I used to run a wireless Scangauge that consisted of a module that plugged into the OBD-II connector and communicated via Bluetooth to an app on my phone. And I had installed a OBD-II Y-cable so I could connect the scangauge module to one side, and leave the other side open for diagnostic purposes. Even though I no longer used the wireless Scangauge, the module was still plugged in and I pretty much forgot it was there. Once he disconnected the Y-cable, thereby disconnecting the module, it all worked like a charm. He was now able to see the ECU on the analyzer. He drove it up and down the road for a couple of laps and it was all good. No errors, no warning lights.

As far as the blown fuse, it was a separate issue. I have an air pressure gauge mounted south-east of the steering column where the right-side coin tray is/was. It has a light in it that taps off the circuit for the dash lights. The bulb had been flickering and then quit; probably blowing the fuse when it did.