Diagnostics - Printed Circuit Board (PCB) Relays

Refer to the wiring information before starting diagnostics to determine if the relay being tested is a Low Side Driver (LSD) or High Side Driver (HSD) controlled relay and where the power supply or grounding location is for the relay. The diagnostic paths below will be different based on relay control method.

RELAY CONTROL CIRCUIT DIAGNOSTIC - LOW SIDE DRIVER: 

1. Using the wiring information, check all fuses that supply battery voltage to the relay being tested. In some cases a relay may receive voltage from the output of another relay. In those cases the fuse(s) that power that relay should also be checked.
   1. If a fuse is open, replace the fuse and retest the relay operation. The battery supply for the coil side of some relays will also power the output of the relay. Check the relay output circuit(s) for a short, or intermittent short to ground.
   2. If the fuse(s) are good, continue to step 2  .
2. This step is intended to determine if the relay is stuck closed. Using a 12-volt test light or DVOM connected to ground, back probe the relay output circuit. There should be no voltage present when the relay is de-energized. This must be performed when the relay is not being commanding closed by the Electronic Control Unit (ECU).
   NOTE:

   If the voltage supply is coming from another relay, either verify that the other relay is being turned on or back probe the control circuit and jump to 12 volts or ground depending on how that relay is controlled (LSD or HSD) to energize the relay.

   1. If battery voltage is present, the relay is stuck closed. Disconnect the PDC connector and ECU harness connector to isolate the relay control circuit and check for continuity between the relay control circuit and ground. There should be no continuity with the circuit isolated.
      • If there is continuity between the relay control circuit and ground, repair the relay control circuit for a short to ground.
      • If there is no continuity to ground, reconnect the ECU harness connector and verify the ECU driver is not stuck on. If the ECU driver is good, replace the PDC in accordance with the service information. If the ECU driver is stuck closed, replace the ECU in accordance with the service information.
   2. If battery voltage is not present, continue to step 3  .
3. This step is intended to try and energize the relay coil. Using a 12-volt test light connected to ground, back probe the relay control circuit at the PDC harness connector. The relay should close and battery voltage should be present on the output circuit. The relay may also make an audible click that can be heard. Check the output circuit for battery voltage present.
   NOTE:

   If the voltage supply is coming from another relay, either verify that the relay is being turned on or back probe the control circuit and jump to 12 volts or ground depending on how that relay is controlled (LSD or HSD) to energize the relay.

   1. If battery voltage is present with the relay control circuit grounded, the relay and PDC are good. Continue to step 4  .
   2. If battery voltage is not present on the output circuit, and the fuses were good, replace the PDC in accordance with the service information.
4. Disconnect the PDC connector and ECU harness connector to isolate the relay control circuit. Check the relay control circuit for an open or high resistance. Typically the circuit should have less than 3.0 Ohms.
   1. If the resistance is above 3.0 Ohms, repair the relay control circuit for an open or high resistance.
   2. If the resistance is below 3.0 Ohms, replace the Electronic Control Unit (ECU) in accordance with the service information.

RELAY CONTROL CIRCUIT DIAGNOSTIC - HIGH SIDE DRIVER: 

Refer to the wiring information before starting diagnostics to determine where the power supply or grounding location is for the relay.

1. Using the wiring information, check all fuses in the PDC.
   1. If a fuse is open, replace the fuse and retest the relay operation. Check the relay output circuit(s) for a short, or intermittent short to ground.
   2. If the fuse(s) are good, continue to step 2  .
2. This step is intended to determine if the relay is stuck closed. Using a 12-volt test light or DVOM connected to ground, back probe the relay output circuit. There should be no voltage present when the relay is de-energized. This must be performed when the relay is not being commanding closed by the Electronic Control Unit (ECU).
   NOTE:

   If the voltage supply for the relay output is coming from another relay, either verify that the other relay is being turned on or back probe the control circuit and jump to 12 volts or ground depending on how that relay is controlled (LSD or HSD) to energize the relay.

   1. If battery voltage is present, the relay is stuck closed. continue to step 3  .
   2. If battery voltage is not present, continue to step 4  .
3. Back probe and check for voltage on the relay control circuit at the PDC connector. There should be no voltage on the circuit if the relay is not being commanded on.
   1. If voltage is present, isolate the circuit by disconnecting the PDC connector and ECU harness connector. Check the control circuit for voltage.
      • If voltage is still present, repair the relay control circuit for a short to voltage.
      • If no voltage is present, replace the Electronic Control Unit (ECU) in accordance with the service information.
   2. If there is no voltage, replace the PDC in accordance with the service information. If the ECU driver is stuck closed, replace the ECU in accordance with the service information.
4. This step is intended to try and energize the relay coil. Using a 12-volt test light connected to Fused B+, back probe the relay control circuit at the PDC connector. The relay should close and battery voltage should be present on the output circuit. The relay may also make an audible click that can be heard. Check the output circuit for battery voltage present.
   NOTE:

   If the voltage supply is coming from another relay, either verify that the relay is being turned on or back probe the control circuit and jump to 12 volts or ground depending on how that relay is controlled (LSD or HSD) to energize the relay.

   1. If battery voltage is present with the control circuit jumped to B+, the relay and PDC are good. Continue to step 5  .
   2. If battery voltage is not present on the output circuit, and the fuses were good, replace the PDC in accordance with the service information.
5. Disconnect the PDC connector and ECU harness connector to isolate the relay control circuit and check for continuity between the relay control circuit and ground. There should be no continuity with the circuit isolated.
   1. If there is continuity between the control circuit and ground, repair the control circuit for a short to ground.
   2. If there is no continuity between the control circuit and ground, continue to step 6  .
6. Check the relay coil ground circuit by load testing the circuit. Read the CIRCUIT LOAD TESTING PROCEDURE for information on building a simple load test tool, additional load testing information and alternative methods of load testing or voltage drop testing a circuit, Refer to CIRCUIT LOAD TESTING PROCEDURES .
   NOTE:

   A way to verify that there is no resistance in the circuit being tested is to perform a simple voltage drop test across the 3156 bulb of the load test tool. The voltage drop across the bulb should be equal to the voltage reading across the Battery terminals if there is no resistance in the circuit being tested.

   1. If the ground circuit fails load testing, repair the relay coil ground.
   2. If the ground circuit tests good, continue to step 7. 

      Courtesy of CHRYSLER GROUP, LLC

7. Check the relay control circuit for an open or high resistance. Typically the circuit should have less than 3.0 Ohms.
   1. If the resistance is above 3.0 Ohms, repair the relay control circuit for an open or high resistance.
   2. If the resistance is below 3.0 Ohms, replace the Electronic Control Unit (ECU) in accordance with the service information.

   Courtesy of CHRYSLER GROUP, LLC