2005 Automatic Transmission, Intermittent P0500 Code, Speedometer Works

I've had an intermittent P0500 Code that I have kept clearing away for the past few months because driving seema unaffected. (We've had to deal with a bunch of repairs for my wife's vehicle, so mine has taken a back seat because it runs just fine and hers needed some serious repairs).

The lights that come on are as follows:
Check Engine Light
Slip Indicator Light
VSC TRAC
VSC OFF

My speedometer works fine.

We're low on money from my wife's car's repairs, so I need (if it exists) a simple, straightforward troubleshooting procedure to fix the problem. I have a multimeter and an OBD2 scanner that I can use.

The last thing I want is to just start replacing components and end up spending a thousand dollars just to find out my ECM needs replacing or some crap like that.
If I need it replaced I wanna know about it right away.

I've looked at other forums, sounds like it could be an ABS thing based on what they say. But I'm not sure how to check for that and I want to make sure I don't miss it if there's a different problem at hand, and my ABS Light doesn't come on.

 

If your speedometer always works then it's most likely not an ABS problem.
On automatic trucks the vehicle speed signal is generated by the rear ABS sensors, the ABS module then sends it to the instrument cluster (Combination Meter) and the cluster then sends it out to the PCM, 4WD ECU (if equipped), Tire Pressure Monitor ECU, Power Inverter (if equipped), and Accessory Meter (if equipped).

The most common cause of a P0500 when the speedometer stays working is the instrument cluster but it can also be an open or shorted SPD wire or one of the modules on the SPD circuit pulling the signal down.

An oscilloscope is the best tool for diagnosing the SPD circuit but some of the tests can be done with a meter.

 

You need to be able to scan the ABS/VSC to diagnose it.

If the ABS module is dead it can cause this. The ABS light should turn on when key is on engine off.

Read up on the stuff DM93 listed, it sounds like you're using caution, which is good, most people throw parts at p0500. It really can be a lot of things.

 

Wouldn't it be safe to assume the ABS is fine since the speedometer works because the speedometer comes after the ABS in the chain of signals?
The VSC light is likely on because the engine light is on.

 

I mis read and he said no abs light so I assumed he meant it was failing the key check. I still think reading it would help. Most obd can’t talk to them.

 

Agreed it can't hurt to read the codes from all the modules (typically my first step on most dignostics) although most DIY scan tools can typically only access the PCM.
I've been meaning to get a known good speed signal capture off my truck but I havent had time, IIRC from my testing when doing the 4wd writeup it's a 0-12v square wave.

 

If I lived closer, we could use my truck as a test pig for the Auto.
Or, you could drive to Tennessee. And after your done with my truck, I got some other stuff you can fix.

 

Only difference between auto and manual trucks on the speed signal is the cluster gets the speed signal from the vehicle speed sensor on the transmission instead of the ABS module, the sequence is the same beyond that.

Manual trucks: vehicle speed sensor > combination meter (speedometer) > PCM & other modules.

Auto trucks: Rear wheel speed sensor > ABS module > combination meter (speedometer) > PCM & other modules.

 

Yeah, well you can still drive up here and confirm it.
Make sure to bring a shovel, mattock, rake, and some 2-stroke gas.