P1604

Symptoms

• Check engine light
• hard starting or extended cranking
• engine fails to start
• intermittent stalling
• including stalling just after start-up. Symptoms are often worse in very cold weather.

Probable causes

• 1) Weak or failing battery
• corroded battery terminals. 2) Fuel system issues: clogged fuel filter
• failing fuel pump
• low-quality fuel. 3) Ignition system faults: worn spark plugs
• faulty ignition coils. 4) Wiring or electrical connection problems in the starting system. 5) Faulty starter motor or ignition switch. 6) Malfunctioning ECM (less common). Extremely cold weather can also trigger the code by weakening the battery and thickening fuel.

Diagnostic steps

1. Test battery voltage (sources state at least 12.6 V fully charged) and inspect terminals for corrosion.
2. Check for companion codes (P1603, P1605) with a scan tool — they narrow down the cause.
3. Measure fuel pressure with a gauge; check for clogged fuel filter, lines, or injectors.
4. Inspect spark plugs for wear and test ignition coils.
5. Inspect starting-system wiring and connections; test the starter motor and ignition switch.
6. If all of the above pass, evaluate the ECM. Note: driving with this code is not recommended — the vehicle can stall unexpectedly or fail to restart.