Diagnostic Test

INTERMITTENT CONDITION
1. Turn the ignition on.
2. With the scan tool, clear all FCM DTCs.
3. Actuate the Trailer Tow Lamps.
4. With the scan tool read the DTC information.
  Does the scan tool read: B166C-LEFT TRAILER TOW LAMP CONTROL CIRCUIT HIGH?
  
  Yes
  - Go to step 2
  No
  - The condition that caused the symptom is currently not present. Inspect the related wiring for a possible intermittent condition. Look for any chafed, pierced, pinched, or partially broken wires.
  - Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
LEFT TRAILER TOW RELAY
1. Turn the ignition off.
2. Remove and install a known good relay in place of the Left Trailer Tow Relay.
  Do the Trailer Tow Lamps operate normally?
  
  Yes
  - Replace the Left Trailer Tow Relay in accordance with the Service Information.
  - Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
  No
  - Go to step 3
FRONT CONTROL MODULE (FCM)

Fig 1: Checking Left Trailer Tow Brake Lamp Relay Control Circuit
Courtesy of CHRYSLER LLC
1. Turn the ignition off.
2. Disconnect the 49 way FCM IPM harness connector.
3. Remove the Left Trailer Tow Relay from the IPM.
4. Remove the FCM from the IPM.
5. Measure the voltage of the (L655) Left Trailer Tow Brake Lamp Relay Control circuit and ground.
  Is the voltage above 1.0 volt?
  
  Yes
  - Replace the Integrated Power Module (IPM) in accordance with the Service Information.
  - Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .
  No
  - Replace the Module Front Control (FCM) in accordance with the Service Information.
  - Perform the BODY VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Front Control (FCM) - Standard Procedure .