DTC P1644: MOTFSA Motor Control Module Signal Malfunction; DTC P1645: MOTFSB Motor Control Module Signal Malfunction; DTC P1646: MOTSTB Motor Control Module Signal Malfunction

NOTE:

Information marked with an asterisk (^*1 ) applies to DTC P1645; information marked with (^*2 ) applies to DTC P1646.
Before you troubleshoot, record all freeze data and review the general troubleshooting information (see GENERAL TROUBLESHOOTING INFORMATION ).

Reset the ECM with the HDS (see ECM RESET ).
Turn the ignition switch ON (II).
Check for Temporary DTCs or DTCs with the HDS.
Is DTC P1644, P1645, or P1646 indicated?
1. YES - Go to step 4.
2. NO - Intermittent failure, system is OK at this time. Check for poor connections or loose terminals at the motor control module and the ECM.
Turn the ignition switch OFF.
Remove the IPU cover (see POWER CONTROL UNIT (PCU) REMOVAL/INSTALLATION ), and disconnect motor control module connector A (32P).
Turn the ignition switch ON (II).
Measure voltage between ECM connector terminal D2, (D1)^*1 , (D3)^*2 and body ground.

Fig 1: Measuring Voltage Between ECM Connector Terminal D2, (D1)^*1 , (D3)^*2 And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there about 5 V?
1. YES - Go to step 11.
2. NO - Go to step 8.
Turn the ignition switch OFF, and wait for 10 seconds.
Disconnect ECM connector D (16P).
Check for continuity between ECM connector terminals D2, (D1)^*1 , (D3) ^*2 and body ground.

Fig 2: Checking Continuity Between ECM Connector Terminals D2, (D1)^*1 , (D3) ^*2 And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES - Repair short in the wire between the ECM (D2, (D1) ^*1 , (D3) ^*2 ) and the motor control module.
2. NO -Update the ECM if it does not have the latest software, or substitute a known-good ECM; 2000-2001 M/T models (see HOW TO SUBSTITUTE THE ECM FOR TESTING PURPOSES (2000-2001 M/T MODELS) ), 2002-2006 M/T models and CVT model (see ECM UPDATING AND SUBSTITUTION FOR TESTING-2002-2006 M/T MODELS AND CVT MODEL ), then recheck. If the symptom/indication goes away with a known-good ECM, replace the original ECM (see ECM REPLACEMENT ).
Turn the ignition switch OFF, and wait for 10 seconds.
Disconnect ECM connector D (16P).
Check for continuity between ECM connector terminal D2, (D1) ^*1 , (D3) ^*2 and motor control module connector terminal A16 (A15) ^*1 (A4) ^*2 .

Fig 3: Checking Continuity Between ECM Connector Terminals D2, (D1) ^*1 , (D3) ^*2 And Motor Control Module Connector Terminals A16 (A15) ^*1 (A4) ^*2
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES - Replace the battery module.
2. NO - Repair open in the wire between ECM connector terminal D2 (D1) ^*1 (D3) ^*2 and the motor control module.