P1604

P1604 on Toyota is Startability Malfunction, which the ECM sets when extended cranking, multiple crank attempts, or rough running during the first 5 to 20 seconds after start exceeds calibrated thresholds; it's a symptom-class code rather than a specific-component code. The ECM is essentially saying the engine is hard to start or runs poorly on cold start, and the actual root cause sits in fuel pressure, ignition energy, compression, sensor drift, or cold-start enrichment logic. Cheapest ladder: scan for any concurrent codes first (P0171/P0174 lean, P0300-P030X misfire, P0420 cat efficiency) because P1604 frequently sets alongside the real fault. Verify fuel pressure on key-on, engine-off (most port-injected Toyotas spec 38 to 44 psi for at least 5 minutes), inspect for fuel injector seepage by cycling key-on three times then watching pressure decay, and pull the spark plugs to check condition (look for fuel-fouled plugs indicating a leaking injector, or oil fouling indicating valve guide wear). The expensive misdiagnosis is replacing the cam timing components or pulling the engine on suspected compression loss when the actual fault is a single leaking fuel injector that bleeds rail pressure overnight.

Vehicle-specific patterns: Toyota 2GR-FE 3.5L V6 (Camry, Avalon, Sienna, Highlander 2007-2014) sees P1604 commonly from leaking fuel injectors that drain rail pressure between starts. Toyota 2AZ-FE 2.4L (Camry, RAV4 2002-2009) sets P1604 from a combination of carbon-fouled injectors and the engine's known oil-consumption-driven plug fouling. Toyota 1NZ-FE 1.5L (Prius NHW11/20, Echo, Yaris 2000-2012) sets P1604 most often from a drifting ECT sensor giving the ECM bad cold-start enrichment data. Toyota 2JZ-GE and 1JZ-GTE (Supra, GS300, IS300 1993-2005) sees P1604 from aging fuel pressure regulator diaphragms leaking fuel into the intake vacuum. Estimated repair: $25 to $980.