Code
P1601
DS
P — Powertrain
Ignition-on ECU supply control
Views:
UK: 2
EN: 2
RU: 2
AI status
Completed
Completed
100%
Causes
- Blown fuse or fusible link for ECU power circuit
- Faulty ignition (RUN/ON) switch or ignition lock wiring
- Faulty power/ECU supply relay or controlling transistor
- Open or short in ECU supply wiring or poor connector pin contact
- Battery voltage low or poor battery connections
- Corroded or loose ground at ECU/engine/body
Symptoms
- Engine may not start or cranks but does not run
- MIL/Check Engine lamp illuminated
- Loss of ECU communication on scan tool at key‑on
- Intermittent electrical faults or ECU resets
- Accessory or dash power anomalies with key in ON position
What to check
- Verify battery voltage and battery terminal tightness (battery >= 12.4 V recommended)
- Inspect and test fuses and fusible links for ECU power circuits
- Visually inspect ECU power/ground connectors for corrosion, bent pins, or damage
- Measure voltage at ECU primary power pin(s) with key OFF, ON, and CRANK
- Check continuity and resistance of ignition feed and ground circuits to ECU
- Verify operation of ECU power relay or solid‑state power driver (if fitted)
Signal parameters
- Battery voltage (key OFF): ~12.0–12.8 V (vehicle dependent)
- Battery voltage (key ON): should be ~battery voltage, not significantly lower
- ECU main supply pin (key ON): ~battery voltage (within ~0.5 V)
- ECU supply pin (crank): should remain near battery voltage (may dip slightly)
- Supply control signal (if controlled): expected relay coil feed or transistor drive (ON = battery, OFF = 0 V)
- Ground resistance ECU to chassis: typically < 1 ohm
Diagnostic algorithm
- Record freeze‑frame data and all stored codes. Do not assume P1601 is only issue.
- Check and confirm battery state of charge and terminal condition. Recharge or replace if low.
- Visually inspect all fuses/fusible links related to ECU power; replace any blown fuses and retest.
- With a DVOM, measure voltage at the ECU main power pin(s) and compare with battery voltage with key OFF, ON, and during crank. Note any large voltage drop.
- If ECU supply is missing, trace back wiring to find open or short. Check for corrosion or damage in harness near bulkheads, firewall, and battery.
- Test ignition switch output circuits: verify the RUN/ON terminal provides battery voltage when key in ON position.
- Locate and verify operation of any ECU supply relay or power control transistor. Swap relay with known good (if appropriate) or bench test relay driver circuit.
- Check ECU ground connections for tightness and continuity to chassis/engine; clean and secure grounds as needed.
- If external wiring and power devices test good, suspect internal ECU supply/control fault. Confirm with manufacturer‑specific bench tests or consult dealer technical data before replacing ECU.
- After repairs, clear codes and verify the fault does not return under the same test conditions; perform road test and re‑scan.
Likely causes
- Blown ECU power fuse or fusible link
- Open/shorted ignition feed wire to ECU
- Faulty ignition switch contacts
- Supply relay coil or driver (solid state) failed
- Loose/corroded ECU connector or ground
Fault status
Status
Ignition‑on ECU supply control — ECU supply circuit not within expected parameters when ignition switched ON.
Repair difficulty: Medium
Diagnostic time: 1.0 - 2.5 hours
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