Wiring pin#34 to ecm ground

[Rick P]

I tried to wire pin34 P59 ecm to ecm ground and when I start the scanner it shows D2,after I start my truck it goes to D1,I need this to read neutral what am I missing here. 86 C30 lq4 with turbo 400

[Overdrive915]

I will read D2 until it picks up a rpm signal above app 400 rpm then it will go to D1. The Th400 is not a electronic box therefore it does not have a park neutral switch that is why you will get that reading. I will also throw trans codes.

[Rick P]

I know the turbo 400 isn't electric hence the reason you ground out pin#34,but for whatever reason it isn't switching to neutral

[Overdrive915]

Pin #34 that is only a external Park Neutral switch. The PCM is waiting for a signal from the transmission pressure switch which is inside the electronic box . The signal it is waiting for is A 12V B 0V C 12V which tells the PCM it is in Park or Neutral as they both have the same values. So when you switch the ignition on A 12V B 12V C 12V that is the reason for you getting D2. The signal for the trans is done internally not externally. Blue Pin #32,72, 34 is the trans range switch instrument cluster. Blue Pin #17 B 18 C and Green Pin #63 A are the internal pressure switch where the PCM gets the signal from. Neutral or Park would be Green Pin #63 12V Blue Pin #17 0V and Pin #18 12V would tell the PCM it is in P or N. There are 5 pressure switches on the valve body 3 n/o and 2 n/c that will determine the logic switching of the trans gear its in.