Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P1647 (2): Power Command Signal Circuit High Input; DTC P16B4 (2): Power Command Signal Circuit High Input
- Information marked with an asterisk (*) applies to 2005-2006 models.
- Information marked with double asterisk (**) applies to 2000-2004 models.
- If DTCs P1647 (2)** (P16B4 (2) *), P1647 (4)** (P16B6 (4)*), and P1647 (6)**(P16B8 (6)*) are stored at the same time after the ECM is updated, do the troubleshooting for DTC P1647 (7)** (P16B9(7)*) (see DTC P1647 (7): MODE SIGNAL CIRCUIT 2 PROBLEM; DTC P16B9 (7): MODE SIGNAL CIRCUIT 2 PROBLEM ).
- Turn the ignition switch ON (II) and watch the MIL.
Does the MIL come on for the first 2 seconds?
- YES - Go to step 2.
- NO - Do the MIL circuit troubleshooting, 2000-2004 models (see 2000-2004 MODELS ), 2005-2006 models (see 2005-2006 MODELS ), and recheck.
- Reset the MCM (see HOW TO RESET THE MCM ).
- Turn the ignition switch ON (II).
Is DTC P1647 (2)** (P16B4 (2)*) indicated?
- YES - Go to step 4.
- NO - Intermittent failure, system is OK at this time. Check for poor connections or loose terminals at the ECM and at the MCM.
- Turn the ignition switch OFF.
- Disconnect ECM connector D (16P).
- Turn the ignition switch ON (II).
- Measure voltage between ECM connector terminals D8 and B20.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there about 5 V?
- YES - Substitute a known-good ECM; 2000-2001 models (see HOW TO SUBSTITUTE THE ECM FOR TESTING PURPOSE (2000-2001 M/T MODELS) ), 2002-2006 models (see ECM UPDATING AND SUBSTITUTION FOR TESTING-2002-2006 M/T MODELS AND CVT MODEL ), and recheck. If the symptom/ indication goes away, replace the original ECM.
- NO - Go to step 8.
- Turn the ignition switch OFF.
- Turn the battery module switch OFF (see TURNING OFF POWER TO THE HIGH VOLTAGE CIRCUIT ).
- Remove the IPU lid (see TURNING OFF POWER TO THE HIGH VOLTAGE CIRCUIT ).
- Turn the ignition switch ON (II).
- Measure voltage between MCM connector terminals C2 and A24.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there about 5 V?
- YES - Repair open in the wire between the MCM (C2) and the ECM (D8).
- NO - Substitute a known-good MCM, turn the battery module switch ON, and recheck. If the symptom/indication goes away, replace the original MCM.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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