Diagnostic Test

WARNING: This page is about a different car, the 2015 Fiat 500. However, it is still accessible from the selected car via links, so may be relevant.

ACTIVE DTC
NOTE:
Make sure the Stop Lamp Switch is properly adjusted before continuing.
1. Ignition on, engine not running.
2. With the scan tool, select View DTCs.
3. Press and release the Brake Pedal.
  Is the DTC Active at this time?
  
  Yes
  - Go To 2
  No
  - Perform the INTERMITTENT CONDITION diagnostic procedure. Refer to INTERMITTENT CONDITION .
CHECK THE (L56) BRAKE LAMP SWITCH OUTPUT CIRCUIT FOR A SHORT TO GROUND
1. Turn the ignition off.
2. Disconnect the Stop Lamp Switch harness connector.
3. Disconnect the PCM C1 harness connector.
4. Disconnect the Center High Mount Stop Lamp harness connector.
5. Measure the resistance between ground and the (L56) Brake Lamp Switch Output circuit at the Stop Lamp Switch harness connector.
  Is the resistance above 10k Ohms?
  
  Yes
  - Go To 3
  No
  - Repair the short to ground in the (L56) Brake Lamp Switch Output circuit.
  - Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST, 16V Turbo .
CHECK THE (L56) BRAKE LAMP SWITCH OUTPUT CIRCUIT FOR AN OPEN
1. Measure the resistance of the (L56) Brake Lamp Switch Output circuit between the Stop Lamp Switch harness connector and the appropriate terminal of the PCM C1 harness connector.
  Is the resistance below 5.0 Ohms?
  
  Yes
  - Go To 4
  No
  - Repair the open in the (L56) Brake Lamp Switch Output circuit.
  - Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST, 16V Turbo .
STOP LAMP SWITCH
1. Measure the resistance between terminal 1 and terminal 2 at the Stop Lamp Switch.
2. Next, measure the resistance between terminal 3 and terminal 4 at the Stop Lamp Switch.
3. Apply and release the Stop Lamp Switch while monitoring the Ohmmeter.
  Does the resistance change from below 5.0 Ohms to an open circuit for one or both of the measurements taken?
  
  Yes
  - Go To 5
  No
  - Verify that there is good pin to terminal contact in the Switch and Powertrain Control Module harness connectors. If OK, replace the Stop Lamp Switch. Refer to SWITCH, STOP LAMP, REMOVAL .
  - Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST, 16V Turbo .
POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Stop Lamp Switch and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the Switch and Powertrain Control Module harness connectors.
4. Perform any Technical Service Bulletins that may apply.
  Were there any problems found?
  
  Yes
  - Repair as necessary.
  - Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST, 16V Turbo .
  No
  - Replace and program the Powertrain Control Module in accordance with the Service Information. Refer to MODULE, POWERTRAIN CONTROL, REMOVAL .
  - Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST, 16V Turbo .