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

WARNING: This page is about a different car, the 2013 Honda Fit, 2012 Honda Fit, 2011 Honda Fit, 2010 Honda Fit, and 2009 Honda Fit. However, it is still accessible from the selected car via links, so may be relevant.

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. (See COMPONENT REPLACEMENT/INSPECTION AFTER DEPLOYMENT ).
Before doing this troubleshooting procedure, review SRS PRECAUTIONS AND PROCEDURES , General Troubleshooting Information (see DTC (DIAGNOSTIC TROUBLE CODES) and BATTERY TERMINAL DISCONNECTION AND RECONNECTION .
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 (see SRS UNIT UPDATE ) and retest.

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.
Clear the DTCs with the HDS (see CLEAR THE DTC MEMORY ).
Turn the ignition switch to ON (II), then wait for 10 seconds.
Check for the DTCs with the HDS (see READING THE DTC ).
Is DTC 56-21, 56-31, 56-22, 56-23, 56-32, or 56-33 indicated?

YES - Go to step 5.

NO - Intermittent failure, the system is OK at this time. Go to TROUBLESHOOTING INTERMITTENT FAILURES . If another DTC is indicated, troubleshoot the DTC.
Turn the ignition switch to LOCK (0).
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 MIL CIRCUIT TROUBLESHOOTING .

NO - Go to step 7.
Turn the ignition switch to LOCK (0).
Jump the SCS line with the HDS.
Disconnect ECM/PCM connector A (49P) from the ECM/PCM (see ECM/PCM REPLACEMENT ).
Disconnect the negative cable from the battery, then wait at least 3 minutes.
Disconnect SRS unit connector A (39P) from the SRS unit (see step 10 under Disconnecting System Connectors ).
Check for continuity between SRS unit connector A (39P) terminal No. 16 and ECM/PCM connector A (49P) terminal No. 4, and between SRS unit connector A (39P) terminal No. 17 and ECM/PCM connector A (49P) terminal No. 3.

Fig 1: Measuring Resistance Between SRS Unit Connector A (39P) & ECM/PCM Connector A (49P)
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES - Faulty SRS unit or poor connection at SRS unit connector A (39P) and the SRS unit. Check the connection between the connector and the SRS unit. If the connection is OK, replace the SRS unit (see SRS UNIT REPLACEMENT ).

NO - Open in the harness between the SRS unit connector A (39P) terminal No. 16 and ECM/PCM connector A (49P) terminal No. 4, or between the SRS unit connector A (39P) terminal No. 17 and ECM/PCM connector A (49P) terminal No. 3 (left engine compartment wire harness or the dashboard wire harness); replace the faulty harness, then clear the DTC.