P0502 code with bad attitude

Hi all.
Here's a brain teaser for you. Dealing with an ongoing P0502 code "Vehicle Speed Sensor Circuit Low Input". This code pops up intermittently and, the speedometer drops out when the code is present. The vehicle runs a VR type sensor. The sensor and associated wiring have all been confirmed as functional. The sensor output has been monitored whilst the vehicle is in motion and it outputs an varying AC voltage ranging between 0-5v Ac. The same voltage is also seen when the code is not present and the speedometer is working fine. Although I'd like the opportunity to hook up to a known good vehicle to see what it outputs at varying speed rangers. The sensor is also an OEM GM replacement, replaced around two years ago (back then replaced for different reasons. Reluctor wheel came loose on the transmission shaft and tore the nose off the original sensor). And it has only done around 10,000 Kms since replaced. The culprit vehicle has a PIM module. The P0502 code is being generated by the PIM module (not the main ECU). The VSS signal is received by the PIM. Now, I can hook up a scan tool and clear the code and this may sometimes work in that the speedometer starts working and all is well. Other times I can clear the code and it comes straight back again as if its a hard fault. But it's not a hard fault because as mentioned, the Sensor is functional whilst this code is logged. Lately I clear the code and it just keeps coming right back. How I do combat this problem? Disconnect the wiring harnesses (2) from the PIM module. This must do some sort of hard reset. Doing it this way seems to have the most positive effect towards eradicating the code for the longer term. Meaning the code could disappear for weeks may be longer. Ok, here we go. Although the OEM VR sensor is relatively new, in that it's only done very few miles, is it possible it's throwing an intermittent low voltage output to the PIM module? Anythings possible I guess. But on the several occasions it was monitored for performance, it worked fine. But I guess I'll be throwing another sensor in shortly as there is no other options. Oh, by the way, I have easy access to a replacement PIM module. A replacement PIM module was programmed and tested in the vehicle and it too threw a P0502 Code. My understanding is the PIM modules cannot be re programmed on the GM SPS system (in case it's a software issue). I've been on the SPS system and there is no option for reprogramming of PIM modules. They must come pre loaded with software. Can't say for sure.

Like with any other issue, check inputs & outputs.Check when it is working & then when it isn't, then see what has changed. Just because you have replaced the sensor in the past, doesn't mean it is still good now. You didn't give us any vehicle specifics, so it's hard to say anymore without being there.

Thanks for the reply.
2008 Isuzu, 3.6 lt, V6, manual. Inputs and outputs have been checked. Both when problem exists and not. Results are the same. As mentioned, VR senor tested and working fine when P0502 code is current. Although one thing I'm not sure of, the specific AC voltage amplitude at speed. I've recorded around 5/5.5 AC volts. Doesn't seem to exceed this range under all driving conditions. My educated guess is the VSS is intermittently throwing a low voltage into the PIM. By the time test equipment is hooked up to look for inputs/outputs, the voltage/s are back on track. Also, the code never presents itself when the vehicle is in motion. Always at the next ignition cycle. I think the PIM software is possibly programmed that way. The VR type sensor/s are usually quite reliable. Don't fail too often. Unlike their counterparts the hall effect type. And this sensor being relatively new, puts it in a category whereby you could be excused for discounting it as causing a problem. But I guess always a first time for everything. The battle goes on.

Could you specify the EXACT vehicle data please as there doesn't show up any2008 Isuzu with a 3.6l engine in my SI systems....

I couldn't find anything on it either, so it's not going to be a domestic vehicle. Also some of the terminology he used was alien to me. Unless someone can provide an applicable wiring diagram, there isn't any more I can do. Still, seems like it would be an easy diag, even without a diagram.

Guys, sorry I didn't mention. This is not a USA domestic vehicle. It's an international model. Below is a list of Wikipedia platforms. Mine is actually the "Holden Rodeo". It has a 3.6 lt V6. I think in the States there is a Buick Lacrosse vehicle that runs the same engine.

Chevrolet Colorado
Chevrolet D-Max
Chevrolet LUV D-Max
Holden Colorado
Holden Rodeo
Isuzu KB
Isuzu LB
Isuzu Rodeo
Chevrolet T Series
GMC Canyon[

Also, The sensor in this vehicle is a "Dorman 917-618 Vehicle Speed Sensor"

Maybe it's a short or bad connection in the connector. Has that been verified?

Sent from my LG-US701 using Tapatalk

Thanks for suggestions. Yes, all shorts, opens, have been positively isolated. This is a very intermittent problem. In that it could manifest after weeks or even months. Whenever the code (P0502) is present, a check of inputs/output and operation of the VSS all return positive results. At the moment everything is perfect. In a month or two or even three, Maybe even after three/four weeks (no fixed pattern), the code may pop up again out of the blue. My thoughts are the VSS (although an OEM replacement and not very old, done very few miles) is intermittently throwing a low input signal back to the PIM module ("Powertrain Interface Module") triggering this code. I think this one is probably even challenging for Scannerdanner. Lol!

Update. Looks like it's a fix! Replacement aftermarket (made in Taiwan) VSS, from Amazon, arrived today. Fitted replacement sensor to vehicle and went on a test drive to check its performance. Straight off the bat the replacement sensor was seen to be outputting higher AC voltages than the suspected faulty original. The original OEM sensor was averaging 2.8 -3.4v AC on the highway (hence the P0502 code). Whereas the replacement sensor was seen throwing signal voltages reaching over 6v AC on the highway. Oddly enough, not one service manual for this vehicle listed specific voltages for the VSS under driving conditions. The original OEM sensor had only served for around 8K miles. Not a very good lifespan.. We'll just have to wait and see if the code logs again in the future but today's findings look promising. Also, there was a difference of around 60 ohms between the old and new sensor. I must say it's not often I see a VR type sensor fail. Especially one that's only been in service for around 8K miles. It's almost always the Hall Effect type counterparts that cause the problems.
Finally, I also noted that when the code was logged in the PIM, clearing it with a scan tool wasn't as successful as disconnecting the power supply from the PIM. Disconnecting the power supply seemed to eradicate the code for longer time frames.