DTC 21-01: Excessive Change of the Vehicle Speed Signal; DTC 21-02: Comparison Between the Vehicle Speed and the Engine Speed Signal

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

NOTE:

If the MIL stays on, or the D indicator blinks at the same time as DTC 21-01 or DTC 21-02 is indicated, troubleshoot the PGM-FI system (see GENERAL TROUBLESHOOTING INFORMATION ) or CVT control system (see GENERAL TROUBLESHOOTING INFORMATION ), then recheck for DTC 21-01 or DTC 21-02.
Even though the system is operating normally, the EPS indicator will come on caused by the detecting condition of DTC 21-01 or DTC 21-02, when you raise the engine speed with the vehicle stopped.
The ABS indicator may come on during this troubleshooting. If so, clear the DTC related to the ABS.

Turn the ignition switch to LOCK (0).
Raise the vehicle on a lift (see LIFT AND SUPPORT POINTS ), and allow all four wheels to rotate freely.
Connect the HDS to the data link connector (DLC).
Start the engine, then run the vehicle in D position.
Check the VEHICLE SPEED in the EPS DATA LIST with the HDS.
Is 0 mph (km/h) indicated?

YES -Go to step 6.

NO -Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the PCM and the EPS control unit.
Turn the ignition switch to LOCK (0).
Start the engine, and check the tachometer.
Is the tachometer working correctly?

YES -Go to step 8.

NO -Troubleshoot the gauge control module (see SELF-DIAGNOSTIC FUNCTION ).
Turn the ignition switch to LOCK (0).
Short the SCS line with the HDS.
Disconnect PCM connector A (44P) and EPS control unit connector C (16P).

Check for continuity between the EPS control unit connector C (16P) terminals and the PCM connector A (44P) terminals individually.

EPS CONTROL UNIT CONNECTOR TERMINAL CHART

Sign	EPS Control Unit Connector C (16P) Terminal	PCM Connector A (44P) Terminal
CANL	9	37
CANH	10	36

Fig 1: Checking Continuity Between EPS Control Unit Connector C (16P) Terminals And PCM Connector A (44P) Terminals

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES -Check for loose terminals in the EPS control unit connectors, and repair if necessary. If no poor connections are found, replace the EPS control unit (see EPS CONTROL UNIT REMOVAL/INSTALLATION ).

NO -Repair an open in the wire between the EPS control unit and the PCM.