Code
P1656
HONDA
P — Powertrain
Automatic Transmission System Malfunction
Views:
UK: 29
EN: 55
RU: 40
AI status
Completed
Completed
100%
Causes
- Low or contaminated automatic transmission fluid (ATF)
- Faulty shift solenoid(s) or solenoid harness
- Damaged wiring or poor connector/ground to TCM/ECM or transmission
- TCM/PCM internal fault or software corruption
- Loss of communication between engine/PCM and TCM (CAN bus)
- Valve body or internal mechanical failure (clutches, bands, pump)
Symptoms
- MIL (check engine light) illuminated
- Transmission goes into limp/backup mode (limited gears)
- Harsh, delayed, or erratic shifting
- No upshift or stuck in one gear
- Transmission slipping or unusual whining/noise
- Reduced engine power or drivability problems
What to check
- Retrieve all stored codes and freeze frame data with a capable Honda scan tool (HDS) or equivalent
- Check ATF level, color and odor; inspect for metal particles
- Inspect wiring harnesses and connectors at the transmission and TCM for corrosion, damage or looseness
- Verify battery voltage and charging system under load
- Confirm CAN/serial communication between PCM and TCM (no U‑codes)
- Perform a visual inspection for fluid leaks and transmission overheating signs
Signal parameters
- Battery voltage: ~12.2–14.8 V (engine running)
- Engine RPM: idle ~600–1200 rpm
- Vehicle speed sensor: matches actual speed (no dropouts)
- Transmission input/turbine speed vs output speed: reasonable ratio for selected gear
- Shift solenoid command duty: 0–100% depending on commanded state
- ATF temperature: typically 30–120 °C in normal operation (varies by model)
Diagnostic algorithm
- Connect a scan tool, record P1656 and any related codes, note freeze-frame and occurrence conditions.
- Clear codes and re-run the vehicle to see if P1656 returns; if intermittent, capture live data during repro.
- Check ATF level and condition; top up or replace if low/contaminated. Re-test.
- Inspect transmission connectors, wiring and grounds; repair any physical damage and ensure good contacts.
- Verify battery and charging system; recharge or replace battery if voltage is low or unstable.
- Monitor transmission inputs/outputs and solenoid commands with scan tool while driving; look for mismatches or stuck solenoid states.
- Measure resistance and operation of individual shift solenoids and compare to spec; check continuity to TCM.
- Check for CAN communication faults (U-codes) and repair bus wiring if present.
- If electrical checks pass and fluid is good, consider valve body or internal transmission component inspection; follow service manual procedures for pressure tests.
- If diagnostics point to control module failure, verify software level and reflash/update TCM/PCM per Honda service information before replacing modules.
- After repairs, clear codes and perform a full road-test and final scan to confirm the fault does not return.
Likely causes
- Low ATF level or degraded fluid allowing slippage or pressure loss
- Failed shift solenoid or solenoid electrical fault
- Poor battery/charging system voltage causing control errors
- Corroded/damaged connector between transmission and TCM
- TCM (transmission control module) fault or firmware issue
Fault status
Status
Automatic Transmission System Malfunction — check transmission, TCM and related wiring/ATF.
Repair difficulty: Medium
Diagnostic time: 1.5-4.0 hours
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