Diagnostic Test

INTERMITTENT CONDITION
1. Turn the ignition on.
2. With the scan tool, clear all Front Control Module (FCM) DTCs
3. Actuate the Trailer Tow Lamps.
4. With the scan tool, read DTCs.
  Does the scan tool read: B166F-RIGHT TRAILER TOW LAMP CONTROL CIRCUIT LOW?
  
  Yes
  - Go to step 2
  No
  - The conditions that caused this code to set are not present at this time. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors.
  - Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
PDC FUSE 21
1. Using a 12-volt test light connected to ground, check the PDC Fuse 21.
  Does the test light illuminate and was the fuse OK?
  
  No
  - Replace the PDC Fuse 21 if open and check for a short to ground on the Relay Output circuit or correct the open B(+) circuit to the fuse.
  - Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
  Yes
  - Go to step 3
OPEN FUSED B(+) TO RELAY
1. Remove the Trailer Tow Relay from the PDC.
2. Using a 12-volt test light connected to ground, check the Fused B(+) circuit at the relay connector.
  Does the test light illuminate?
  
  No
  - Replace the Power Distribution Center in accordance with the Service Information.
  - Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
  Yes
  - Go to step 4
RIGHT TRAILER TOW RELAY
1. Install a known good relay in place of the Trailer Tow Relay.
2. With the scan tool erase DTCs
3. Cycle the ignition from on to off three times and leave on.
4. With the scan tool, read DTCs.
  Does the scan tool display the same DTC?
  
  No
  - Replace the original Trailer Tow Relay in accordance with the Service Information.
  - Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
  Yes
  - Go to step 5
(L656) RIGHT TRAILER TOW BRAKE LAMP RELAY CONTROL SHORTED
1. Remove the Right Trailer Tow Relay.
2. Disconnect the 49 way FCM IPM harness connector.
3. Measure the resistance between ground and the (L656) Right Trailer Tow Brake Lamp Relay Control circuit at the relay.
  Is the resistance below 1000.0 Ohms?
  
  Yes
  - Replace the Power Distribution Center.
  - Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
  No
  - Go to step 6
(L656) RIGHT TRAILER TOW BRAKE LAMP RELAY CONTROL OPEN
1. Measure the resistance of the (L656) Right Trailer Tow Brake Lamp Relay Control circuit from the relay connector to FCM connector.
  Is the resistance below 3.0 Ohms?
  
  Yes
  - Replace the Front Control Module (FCM) in accordance with the service information.
  - Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
  No
  - Replace the Power Distribution Center in accordance with the service information.
  - Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .