Thanks Nick.A low (or otherwise anomalous) TPS voltage signal to the ECM will impact transmission performance/function as the ECM relies on TPS data, among other sensor data flows, to control the transmission. If the TPS was replaced with a non-OEM part, there's always higher risk of it being DOA. If the new part is working correctly, then there's likely a short somewhere between TPS and ECM (including the ECM). I'm not super-informed as to how TPS actually work but my understanding is that they will send a variable voltage signal to the ECM based on throttle position. If the ECM thinks it's not seeing enough voltage at any given point it will store a DTC (usually P0122). Late, harsh or otherwise erratic shifting patterns are most commonly reported and this is when the transmission was previously functioning normally with no previous drivability symptoms.
Given that the replacement TPS I used is an ACDelco part (Gold), let’s assume for the moment that it’s ok.
Add to that my guy’s recollection of the ‘96 being the first year for the VCM, which combined the ECU and TCU, and that same year having shorting issues within the VCM, I have to wonder, as Road Trip has (see below), if the VCM isn’t in fact the culprit.
It also seems highly suggestive that I’m getting ABS codes and lights while this is going on. This is a new occurrence, and roughly corresponds in time to the hard shifting. ABS is also controlled by the VCM.
I agree. It seems to fit the observed facts. I’ll run this past my guy when I talk with him tomorrow, but it seems like as good a working hypothesis as any.So, the previous 5 paragraphs are written from the perspective of the Throttle Position Sensor
as being the perpetrator of the error codes being thrown. As a good troubleshooter, I need to
consider the alternate universe, where the TPS sensor is a victim of a flaky/intermittent +5V reference,
Ground, or the To/From wiring interconnecting the TPS to the engine ground and also the Black Box.
Because of its intermittency, the simplest way to test it, I suppose, would be to install a new VCM. They appear to be available and reasonably priced - around $150. That would require flashing the new VCM so that it will function with the Subdivision. I don’t know if my guy can do it, or if my scan tool is capable of doing it. He may have to refer me to a shop that can do it. Whatever. It will be a topic of conversation.
In any case, I’ll talk with my guy tomorrow and see what he thinks.
This discussion has really been helpful.
Thanks again!