SRS System

Control System DTCs

SRS DTC Troubleshooting: 56-21, 56-22, 56-23

DTC 56-21 : Lost Communication With the PCM (PGM-FI system)
DTC 56-22, 56-23 : Undefined Data Received From the PCM (PGM-FI system)

NOTE:
* Before doing this troubleshooting procedure, find out if the vehicle was in a collision. If so, verify that all the required components were replaced with new components, of the correct part number, and that they were properly installed Service and Repair.
* Before doing this troubleshooting procedure, review SRS Precautions and Procedures Service and Repair, General Troubleshooting Information Reading and Clearing Diagnostic Trouble Codes, and Battery Terminal Disconnection and Reconnection Procedures.
* Before replacing the SRS unit, check the SRS unit software version with the HDS. If the software version is not the latest, update the SRS unit software Programming and Relearning, and retest.


1. Body electrical system check:

-1. Check for any F-CAN and B-CAN communication DTCs with the HDS.

Are there any communication DTCs?
-YES- Go to the appropriate DTC troubleshooting.
-NO- Go to step 2.

2. DTC check:

-1. Clear the DTCs with the HDS Reading and Clearing Diagnostic Trouble Codes.

-2. Turn the ignition switch to ON (II), then wait for 10 seconds.

-3. Check for DTCs with the HDS Reading and Clearing Diagnostic Trouble Codes.

Is DTC 56-21, 56-22, or 56-23 indicated?
-YES- Go to step 3.
-NO- Intermittent failure, the system is OK at this time. Go to Troubleshooting Intermittent Failures Reading and Clearing Diagnostic Trouble Codes. If another DTC is indicated, troubleshoot the DTC.

3. PGM-FI system check:

-1. Turn the ignition switch to LOCK (0).

-2. Start the engine, and see if the malfunction indicator lamp (MIL) also stays on.

Does the MIL stay on longer than 30 seconds?
-YES- Go to the Fuel and Emissions Systems General Troubleshooting Information How to Troubleshoot the Fuel And Emissions Systems.
-NO- Go to step 4.

4. Open wire check (F CAN-H, F CAN-L lines):

-1. Turn the ignition switch to LOCK (0).

-2. Jump the SCS line with the HDS How to Troubleshoot the Fuel And Emissions Systems.

NOTE: This step must be done to protect the PCM from damage.

-3. Disconnect the following connector.






-4. Disconnect the negative cable from the battery, then wait at least 3 minutes.

-5. Disconnect the following connector.






-6. Check for continuity between test points 1 and 2.














Is there continuity?
-YES- The F CAN-H, F CAN-L wires are OK. Faulty SRS unit or poor connection at SRS unit connector A (39P) and the SRS unit. Check the connection; if the connection is OK, replace the SRS unit Service and Repair. If the DTC does not clear, replace the engine compartment wire harness or the dashboard wire harness.
-NO- Open in the harness between SRS unit connector A (39P) terminal No. 20 and PCM connector A (49P) terminal No. 3, or between SRS unit connector A (39P) terminal No. 21 and PCM connector A (49P) terminal No. 4 (engine compartment wire harness or dashboard wire harness); replace the faulty harness, then clear the DTC.