OBD-II Code
P1605
Severity
Not yet reviewed
Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.
Can you drive it
We cannot say
Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.
Indicative cost (USD)
$80–$1,400
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
$80 (single sensor on accessible engines) to $1,400 (sub-harness with intake removal or rebuilt ECM).
P1605 on a Toyota is a Knock Control CPU internal fault — the ECM ran its own internal diagnostic on the knock-control sub-processor (or the dedicated knock-control IC on older two-chip ECMs) and detected an internal failure.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then follow the diagnostic notes further down this page, in the order they are written.
They are written in the order a shop works this code, cheapest checks first. Where they name a component, inspect its wiring and connector before replacing it.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Read the full diagnostic procedureP1605 on a Toyota is a Knock Control CPU internal fault — the ECM ran its own internal diagnostic on the knock-control sub-processor (or the dedicate…
P1605 on a Toyota is a Knock Control CPU internal fault — the ECM ran its own internal diagnostic on the knock-control sub-processor (or the dedicated knock-control IC on older two-chip ECMs) and detected an internal failure. This is one of the rare Toyota P1xxx codes where the ECM is actually the failed part on a non-trivial percentage of cases, but you still walk the cheaper inputs first.
The cheapest-first ladder
- scan live knock-sensor data and watch the piezoelectric voltage signal (0-5V AC peaks during combustion knock events) while gently revving — flat-line zero on both knock sensors usually means a broken sensor wire or a corroded sensor connector, not an ECM failure.
- Next, ohm-out each knock sensor at the connector (typical Toyota knock sensor reads 120-280 kilohms across the element on a flat-response sensor or shows a tuned-resonance frequency curve on the tuned types).
- Then inspect the ECM connectors C24/C25/C26 for green corrosion, especially the ECM ground points on the firewall and intake manifold.
- If knock sensors are healthy and the ECM connectors are clean, an ECM reflash via Toyota Techstream sometimes clears P1605 (firmware bugs on early 2GR-FE and 2UZ-FE platforms).
- Only after all of that should you condemn the ECM. Don't replace the ECM before checking for a single failed knock sensor pulling the bus voltage down — 1UZ-FE / 2UZ-FE / 3UZ-FE engines have two knock sensors wired in parallel, and one shorted sensor can manifest as a CPU-internal fault.
Vehicle-specific patterns1998-2007 Land Cruiser / Lexus LX470 (2UZ-FE) and Tundra/Sequoia 4.7L throw P1605 from the well-known knock-sensor sub-harness failure that lives und…
- 1998-2007Land Cruiser / Lexus LX470 (2UZ-FE) and Tundra/Sequoia 4.7L throw P1605 from the well-known knock-sensor sub-harness failure that lives under the intake manifold — the sensors themselves are buried in the valley and the sub-harness wire insulation breaks down from heat soak; Toyota sells a replacement sub-harness as a single part for around $80, but the labor to pull the intake is 4-6 hours.
- 2007-2017Camry / Avalon / Highlander 3.5L (2GR-FE) throws P1605 from a corroded knock-sensor connector on the rear bank that floods with rainwater entering through the cowl drain.
- 2001-2010Lexus IS300/GS300/LS430 throws P1605 from ECM solder-joint cracks at the knock-control IC pins — TechStream reflash sometimes masks it; a rebuilt ECM is the real fix.
- 2003-20094Runner / FJ Cruiser (1GR-FE) throws P1605 from the same sub-harness pattern as the 2UZ.
Estimated repair$80 (single sensor on accessible engines) to $1,400 (sub-harness with intake removal or rebuilt ECM).
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