If you connect a wire from the 12v feed to the ground, you'll just blow the fuse. Not helpful. Can you get a meter on the EXHVAL signal from the ECU? I think C212 and C213 are in the passenger footwell somewhere. I'm guessing EXHVAL is at around 12v when the valves are closed and 0v when they're open. Is this right, or is it the other way around, or is it something else entirely? By the way, it's all just volts and amps, there's no CAN bus involved in this part of the system.Tried a new switch and still getting the same results.
Switch on. All is good and all works fine. Turn switch off and car throws "drive mode not selectable" within about 3-5 seconds.
According to my voltmeter pin 2 on connector C215 carries a constant 12 volt signal back to the two exhaust valves. My understanding is that the PCM then sends a signal to the valves down the violet wires and through pin 34 at connector C212 and C213 in the same passenger footwell. The only other wire we see in the provided diagram is the ground wire at the actual valves themselves. Is it possible that the PCM is monitoring that 12 volt feed into the exhaust valves somehow? It must be if the wiring above is accurate. Does anyone else have 2018 specific GT350 wiring schematics for the PCM or exhaust valves?
Maybe on the 2018 I need to bypass the solenoids completely and run a jumper wire all the way to the grounds to keep the system happy? It's been a while since I've read wiring schematics and these newer can-bus systems are more complicated than what I'm used to. Would like to get some feedback before I try some shiznit and start popping fuses, relays, and god knows what else. At this point I'd just buy the AWE system, but I'm not 100% confident it will work and the price is now up over $350.
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Update: another thing to check in your service manual, which seems to be a little different than mine (later, I guess) is the error codes for problems with the exhaust valves. That may tell you exactly how it works - the whole section is missing from my 2016 manual, but I'd expect it's in your later one.