Navigation System Symptom Troubleshooting - Display unit buttons or touch screen buttons do not work or respond properly

Display unit buttons or touch screen buttons do not work or respond properly NOTE: If the audio system is malfunctioning, repair the audio system first. Refer to the appropriate audio system troubleshooting. Turn the ignition switch to ACC (I). Go into the Diagnostic mode and use the ‘‘Touch Panel'' test under Monitor Check and, if necessary, the ‘‘Display'' test under Unit Check. Do the buttons work properly?
YES | - | System is OK.■
NO | - | Go to Step 3 .
Try all the buttons on the navigation system. Is there a specific row or columns of buttons, set of button, or a certain button that does not respond properly (i.e. pressing a button in the lower left corner causes a button in the right lower corner to respond.)?
YES | - | Replace the display unit.■
NO | - | Go to Step 4 .
Measure the voltage between body ground and display unit connector B (20P) terminal No. 1 and No. 2 individually. Is there battery voltage?
YES | - | Go to Step 5 .
NO | - | If the +B wire does not have voltage, repair the open in the wire between the under-dash fuse/relay box and the display unit. If the ACC wire does not have voltage, repair the open in the wire between the under-dash fuse/relay box and the display unit.■
Turn the ignition switch OFF. Disconnect the display unit connector B (20P). |

Check for continuity between display unit connector B (20P) terminal No. 10 and body ground. Is there continuity?
YES | - | Go to Step 8 .
NO | - | Repair the open in the wire between the display unit and body ground (G503).■
Disconnect the navigation unit connector A (20P). |

Check for continuity between body ground and display unit connector B (20P) terminal No. 5 and No. 15 individually. Is there continuity?
YES | - | There is a short to body ground in the circuit between the display unit and the navigation unit. Replace the affected shielded harness.■
NO | - | Go to Step 10 .

Check for continuity between display unit connector B (20P) terminal No. 5 and navigation unit connector A (20P) terminal No. 10. Is there continuity?
YES | - | Go to Step 11 .
NO | - | There is an open in the circuit between the display unit and the navigation unit. Check for poor connections or loose terminals at the display and navigation units. If a poor connection or loose terminal is found, replace the affected shielded harness.■

Check for continuity between display unit connector B (20P) terminal No. 15 and navigation unit connector A (20P) terminal No. 20. Is there continuity?
YES | - | Replace the display unit.■
NO | - | There is an open in the circuit between the display unit and the navigation unit. Check for poor connections or loose terminals at the display and navigation units. If a poor connection or loose terminal is found, replace the affected shielded harness.■