Code
P1600
SCION
P — Powertrain
ECM battery malfunction
Views:
UK: 1
EN: 6
RU: 3
AI status
Completed
Completed
100%
Causes
- Weak or discharged battery
- Loose, corroded or damaged battery terminals/cables
- Poor engine/chassis ground or ECU ground connection
- Faulty alternator or charging system
- Blown fuse or fusible link supplying the ECM
- Damaged wiring or connector to the ECM (open/short/intermittent)
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Stored/recurring P1600 and/or other power-related codes
- Loss of learned memory: clock, radio presets, learned fuel trims or idle settings
- No-start or hard-start conditions after battery events
- Random stalling or drivability issues
- Electrical accessories reset or behave erratically
What to check
- Read and record all stored and pending DTCs and freeze-frame data
- Check battery resting voltage (key off) and measure with engine off and cranking
- Perform battery load/test (CCA and state-of-charge)
- Inspect and clean battery terminals and cable ends; check cable condition
- Check main fuses and fusible links for ECM power circuits
- Measure charging system voltage with engine running
Signal parameters
- Battery resting voltage (key off): ~12.4–12.8 V (fully charged)
- Battery voltage (key on, engine off): ~12.0–12.8 V
- Cranking voltage: typically >9.5–10.0 V under load (depends on vehicle)
- Charging voltage (engine running): ~13.5–14.8 V
- ECM supply pin(s) should be near battery voltage when key ON; no rapid drops or spikes
- Ground continuity: near 0 Ω between ECM ground and battery negative
Diagnostic algorithm
- Connect a capable scan tool, read all DTCs and freeze-frame; note any related codes (voltage, memory, CAN bus).
- Visually inspect battery, terminals, cables, fusible links and ECM connector. Repair obvious corrosion/damage.
- Measure and record battery voltage at rest, with key ON, during cranking, and with engine running. Compare to expected ranges.
- Perform a battery load or CCA test; replace battery if it fails.
- Test charging system (voltage and alternator output). Repair/replace alternator or regulator if out of range.
- Check and tighten/clean all engine/chassis grounds and battery terminal connections; re-check voltages.
- Inspect and test ECM power and ground circuits: check continuity, resistance to battery, and inspect fuses/fusible links. Repair wiring as needed.
- If wiring and power/grounds are good, clear codes and perform a controlled power-cycle and a road test while monitoring battery/ECM supply voltage and related live data.
- If code returns with good supply voltages and solid wiring/grounds, consider ECM internal fault; consult manufacturer TSBs and perform ECM bench test or replacement only after confirming external power issues are resolved. Reprogram or relearn as required after ECM replacement.
- Document repairs and recheck for intermittent faults over time.
Likely causes
- Low battery state of charge or failing battery
- Corroded/loose battery positive or negative cable
- Bad ground strap between engine and chassis or poor ECM ground pin connection
- Failed/undercharging alternator or regulator
- Blown main ECU fuse or fusible link
- Intermittent harness/connector fault at the ECM power pins
Fault status
Status
ECM reported a battery/power supply malfunction — voltage out of expected range or loss of battery power to the ECM detected.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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