Code Definition

P1605 — Rough Idling

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Toyota

About P1605

P1605 is a manufacturer-specific powertrain diagnostic trouble code recorded for Toyota vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1605 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The engine control module maintains a target idle speed by trimming throttle opening or idle air bypass while watching crankshaft position sensor pulses to measure how evenly the engine is turning over. It cross references that with throttle position, mass airflow or manifold pressure, coolant temperature, and fuel trim values to judge whether idle quality is within its programmed limits. DTC P1605 is logged when idle speed fluctuation, or the correction the module is having to apply to hold target idle, exceeds the acceptable threshold over a sustained period. The code identifies unstable idl...

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