P0500... again

Having the same problem as so many others before me, with slightly different circumstances. I have the P0500 code. My truck is a '06 OR 5AT for reference. So no VSC or anything. My speedometer and all other gauges in the cluster work just fine. No other lights but the CEL. My cruise control can be switched on, as in the green word CRUISE appears in the cluster, but none of the functions work.

I plugged the truck into Techstream and got the following:
Engine and ECT system- Vehicle Speed = 0 regardless of road speed
SP2 = whatever is displayed on the cluster speedo
ABS System- Vehicle speed = whatever is displayed on the cluster speed
Front left speed = whatever is displayed on the cluster speed
Back left speed = whatever is displayed on the cluster speed
Front right speed = whatever is displayed on the cluster speed
Back right speed = whatever is displayed on the cluster speed
Cruise Control system- vehicle speed = 0 regardless of road speed

So anyway it appears that all ABS sensors and the VSS in the transmission are working properly. What else can I check before resigning myself to the cluster? There's a lot of threads on this but many go off topic or are not concluded by the OP. I'm semi competent but not an EE or an ASE tech.

Thanks all for any help

 

Look into your cluster, ecm, or the wiring in between. Speedometer is getting signal from the sensors on the truck, then forwards it to ecm.

 

It’s possible to check the combination meter output.
You’ll need an oscilloscope. (They aren’t cheap)
I know of only one person that’s actually captured good graphs.

If you are interested in his findings.
https://www.tacomaworld.com/threads/p0500-code-vehicle-speed-sensor.556206/

Here is more good material to help understand the system workings. (It’s where I learned about it)
Actually, @Dm93 is the one that helped me understand it.
https://www.tacomaworld.com/threads/speed-sensor.702360/

 

Ok I’m going to test continuity on the violet/white between cluster plug C9 pin 19 and ECM plug E7 pin 8. And I’ll be thrilled if that’s the issue. However I’m probably unlucky enough that it’s the cluster. Is there any way I can test its output in a rudimentary fashion with a DMM? No oscilloscope for me.

 

Correction violet/white is pin 2 on the cluster side harness. Regardless, there is continuity along that wire to the ECU. So is faulty cluster the only conclusion? What utility is there in removing the circuit board and looking for busted solder connections?

 

Most likely it's the cluster, it seems to be a relatively common problem on 2nd gen automatic trucks.
Not sure what exactly goes bad in them, I haven't seen where anyone took one apart and fixed it.
There are various companies that do cluster and module repair.

 

Would anyone out there have a suggestion on who to go with? Tanin is almost $600 without shipping. Several hundred more than a ‘12-15’ for some reason.

 

Another option would be a used one with similar mileage.

 

Also I have 10.6V on that pin coming off the combination meter going into the harness, and 10.6V on the ECM side of the violet-white wire. Relevant?

 

Circuit board medics.

 

The speed signal is a 0-5v square wave so not sure where the 10.6v is coming from unless your on the wrong pin or a module is faulty.
Should be E7 Pin 8 at the ECM and C9 Pin 19 at the combination meter.
Speed signal is also provided via the same wire to the 4wd ECU (if equipped), power inverter (if equipped), accessory meter (if equipped), and the TPMS ECU, so any of those theoretically could be pulling the signal wire up or down.

 

Those are certainly the pins I tested. I was [am] confused since I’ve also seen the oscilloscope showing a 0-5 square wave. I have those options you listed; pretty sure they were all disconnected though while i was performing the diagnostic. I was having a concurrent problem with 4x4 not engaging, with the cluster lights constantly blinking, but I thought i solved it (or at least 4x4 now works again) by adding a wire overlay. There was some open ground I could never locate. In fact, I started a thread about it and all of you were kind enough to contribute. Mahalo!
@Dm93 @TnShooter @6 gearT444E

 

Well you could unplug the PCM and the cluster and see if the 10.6v is still there, if it is then something is shorted to power either in a module, harness, or connector.

 

Is the DTC test procedure same for 4.0L? That ones for the 2.7. My ECM has one additional harness plug.

I learned (strong exaggeration) a few new things today that may help. Using the DMM, when I test voltage at the PIN 19 on plug C9 on the cluster, I get ~4v (c9 male is unplugged and c10 male is plugged in). When I test the PIN 8 on plug E7 on the ECM, I have about 4.5V. When EITHER end of the harness is plugged in, to the ECM or cluster, and the pin out on the end of the harness is tested, I get ~10v. When both ends of the harness are plugged in, I now get ~10v on pin 19 (contacting the pin on the backside or the circuit board).
Did I accomplish anything?

 

Srry I thought you had a 4.0L but I believe the pin number is the same for the SPD pin.
I got to looking closer at this and it does use a 0-12v square wave so seeing 10.9V there is plausible.

I went and looked at my notes from when I wrote up the 4wd system thread and I showed 0v on the SPD wire at the 4wd ECU when stationary and 0-12v square wave when moving, I have a manual trans but the SPD signal seems to be wired the same coming from the cluster.

 

5V is about bottom of scale, the pulse is generated every 15.75 inches traveled. High end of the pulse is 10-14V for SPD signal. You likely just proved the 5V signal coming from ECM is functioning by unplugging and measuring that voltage.

 

I would unplug E7 at the ECM and C9 at the cluster and take some readings.
Check C9-19 to E7-8 ohm reading, should be zero or very low.
Check C9-19-GND, should be infinite.
You may have a short or a fault where the SPD signal splits out to the other modules (inverter, 4wd ECM, or accessory meter) via the J/B. If you have a ground, start by unplugging the connectors that send speed signal to the other functions and see if your voltage returns.

See if you can borrow a buddies instrument cluster for troubleshooting, that will also help a ton.

 

excuse the bold type it was to show my replies!

 

I didn’t physically take a look at mine to confirm it, I think this should be the one you are looking for.
I have to give credit where it’s due, I pulled most of the pics and diagram from here

https://www.tacomaworld.com/threads/4wd-ecu-location.495036/

 

That’s awesome! Ok I have more helpful but also frustrating info. After all this help, I decided the best next step would be to make a jumper wire between my cluster and the ECM. So with everything plugged in, I jumped from the back of the harnesses at c9-9 to e7-8, bypassing the junction box and everything else. And Wtf do you know, my SP2 readings are now live and accurate, and P0500 is gone. However, my cruise control light now flashes at a rate commensurate with my speed. It seems to be a binary reflection of the square wave speed output from the cluster (of course cruise control doesn’t itself function or I’d make a permanent jumper and leave well enough alone). I’m attaching a video. Never mind apparently videos not allowed. Regardless, the blinking increases with increased speed, and slows down when the truck slows, and turns off when stationary.