Pinpoint Test C: The Transmission Control (TC) Switch Is Inoperative

WARNING: This page is about a different car, the 2005 Ford Mustang. However, it is still accessible from the selected car via links, so may be relevant.

C1 CHECK THE VOLTAGE TO THE TRANSMISSION CONTROL (TC) SWITCH
- Key in OFF position.
- Disconnect: Transmission Control (TC) Switch C279.
- Key in ON position.
- Measure the voltage between TC switch C279-3, circuit 911 (WH/LG), harness side and ground.
  
  Fig 1: Measuring Voltage Between TC Switch C279-3, Circuit 911 Harness Side And Ground
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts?
1. Yes : GO to C2.
2. No : REPAIR the circuit. TEST the system for normal operation.
C2 CHECK THE TC SWITCH
- Measure the resistance between transmission control (TC) switch C279-3 (component side), and C279-4 (component side), while depressing and releasing the TC switch.
  
  Fig 2: Checking The TC Switch
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms with the TC switch depressed and greater than 10,000 ohms with the TC switch released?
1. Yes : GO to C3.
2. No : INSTALL a new TC switch. Test the system for normal operation.
C3 CHECK CIRCUIT 224 (TN/WH) FOR AN OPEN
- Key in OFF position.
- Disconnect: Powertrain Control Module (PCM) C175.
- Measure the resistance between transmission control switch (TCS) C279-4, circuit 224 (TN/WH), harness side and powertrain control module (PCM) C175-29, circuit 224 (TN/WH), harness side.
  
  Fig 3: Checking Circuit 224 (TN/WH) For An Open
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
1. Yes : Refer to INTRODUCTION - GASOLINE article.
2. No : REPAIR the circuit. TEST the system for normal operation.