Pinpoint Test D: The Transmission Control (TC) Switch Does Not Operate Correctly

WARNING: This page is about a different car, the 2006 Mercury Grand Marquis and 2006 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.

D1 CHECK FUSE F26 (10A)
- Check fuse: CJB Fuse F26 (10A).
- Is the resistance less than 5 ohms?
Yes : GO to D3.

No : GO to D2.
D2 CHECK CIRCUIT 640 (RD/YE) FOR A SHORT TO GROUND
- Key in OFF position.
- Disconnect: CJB Fuse F26 (10A).
- Measure the resistance between the output side of fuse F26 (10A) and ground.
  
  Fig 1: Measuring Resistance Between Output Side Of Fuse F26 (10A) And Ground
  Courtesy of FORD MOTOR CO.
- Is the resistance greater than 10,000 ohms?
Yes : GO to D4.

No : REPAIR circuit 640 (RD/YE). REINSTALL all components. TEST the system for normal operation.
D3 CHECK CIRCUIT 640 (RD/YE) FOR AN OPEN
- Key in OFF position.
- Disconnect: CJB Fuse F26 (10A).
- Disconnect: Transmission Control (TC) Switch C279.
- Measure the resistance between the output side of fuse F26 (10A) and TC switch C279-1.
  
  Fig 2: Measuring Resistance Between Output Side Of Fuse F26 (10A) And TC Switch C279-1
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
Yes : GO to D5.

No : REPAIR circuit 640 (RD/YE). RECONNECT all components. TEST the system for normal operation.
D4 CHECK THE SELECTOR LEVER HARNESS FOR A SHORT TO GROUND
- Key in OFF position.
- Disconnect: Transmission Control (TC) Switch C279.
- Measure the resistance between TC switch C279-1 and ground while cycling the TC switch.
  
  Fig 3: Measuring Resistance Between TC Switch C279-1 And Ground While Cycling TC Switch
  Courtesy of FORD MOTOR CO.
- Is the resistance greater than 10,000 ohms?
Yes : GO to D6.

No : INSTALL a new selector lever. REFER to SELECTOR LEVER - COLUMN SHIFT . RECONNECT all components. TEST the system for normal operation.
D5 CHECK THE TRANSMISSION CONTROL (TC) SWITCH
- Key in OFF position.
- Measure the resistance between TC switch C279-1 and C279-2 while cycling the TC switch.
  
  Fig 4: Measuring Resistance Between TC Switch C279-1 And C279-2
  Courtesy of FORD MOTOR CO.
- Does the resistance change from less than 5 ohms to greater than 10,000 ohms?
Yes : GO to D7.

No : INSTALL a new selector lever. REFER to SELECTOR LEVER - COLUMN SHIFT . REINSTALL all components. TEST the system for normal operation.
D6 CHECK CIRCUIT 224 (TN/WH) FOR A SHORT TO GROUND
- Disconnect: Powertrain Control Module (PCM) C175b.
- Measure the resistance between transmission control (TC) switch C279-2 and ground.
  
  Fig 5: Measuring Resistance Between Transmission Control (TC) Switch C279-2 And Ground
  Courtesy of FORD MOTOR CO.
- Is the resistance greater than 10,000 ohms?
Yes : INSTALL a new PCM. RECONNECT all components. TEST the system for normal operation.

No : REPAIR circuit 224 (TN/WH). RECONNECT all components. TEST the system for normal operation.
D7 CHECK CIRCUIT 224 (TN/WH) FOR AN OPEN
- Disconnect: Powertrain Control Module (PCM) C175b.
- Measure the resistance between transmission control (TC) switch C279-2 and PCM C175b-27.
  
  Fig 6: Measuring Resistance Between Transmission Control (TC) Switch C279-2 And PCM C175b-27
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
Yes : INSTALL a new PCM. RECONNECT all components. TEST the system for normal operation.

No : REPAIR circuit 224 (TN/WH). RECONNECT all components. TEST the system for normal operation.