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Message: <blockquote data-quote="clevor" data-source="post: 25102" data-attributes="member: 6998"><p>i have an 03HD chevy with 8.1/Allison. DIC shows range shift inhibited. no reverse, 3rd gear only. 14 trouble codes are displayed on my scan tool for the tcm. So I have had trouble with it before but it cleared up by itself. Dont know why but it did. To help me diagnose any future problems if it did it again I installed a voltmeter and tapped it in the ignition power circuits and ground wires at the tcm gray connector. Ground and power are monitored there in both circuits. I also monitor transmission fluid pressure at the tap with a gauge. None of these gauges show anything amiss when I get the range shift inhibited fault. So I pulled the connectors off the tcm and checked to make sure all of the pins in the connectors were in the correct position. They were. Then I went to the plug on the RR of the trans and pulled it off to check for oil. No oil. Then I pulled the connectors off the nsbu switch and found a pin on the switch pushed in. Replace the nsbu switch, cleared codes and tried it again. No luck. Still have these 14 codes. Then got wiring diagram and saw that there is a 12v reference on pin 31 of the red connector at the tcm. Checked that also with the engine running. I got 13v. So I dont think there are any shorts to ground or bad grounds. Im at a loss. One other thing, those codes will set with just the key on without the engine running. I would appreciate any help yall could give me.</p></blockquote><p></p>