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OBD-II Code

P1166

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)

$30–$440

From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.

P1166 on Honda is an A/F Sensor Heater Power Circuit fault on Bank 1 Sensor 1, distinct from P1163 (sensor performance) in that P1166 specifically targets the +B power feed to the heater coil rather than the heater's low-side driver or the sensing element itself.

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.

  1. 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.

  2. 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.

  3. 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.

  4. 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 procedureP1166 on Honda is an A/F Sensor Heater Power Circuit fault on Bank 1 Sensor 1, distinct from P1163 (sensor performance) in that P1166 specifically ta…

P1166 on Honda is an A/F Sensor Heater Power Circuit fault on Bank 1 Sensor 1, distinct from P1163 (sensor performance) in that P1166 specifically targets the +B power feed to the heater coil rather than the heater's low-side driver or the sensing element itself. The Honda wideband heater draws roughly 1.0 to 2.5 A at operating temperature, with cold inrush briefly higher; the PCM watches heater current and supply voltage and sets P1166 when supply voltage at the sensor's +B pin falls outside spec while the heater is commanded on.

Cheapest ladder

  1. check the PGM-FI main relay (a known Honda weak point that ages out of older Civics and Accords with intermittent symptoms before throwing a hard code), inspect the under-hood fuse box for the AFR heater fuse (commonly 15A), and back-probe the sensor's +B pin key-on, engine-running for battery voltage within 0.3V of the battery itself.
  2. Pull the sensor connector and inspect for green oxidation, melted pins, or pin-back.
  3. Measure heater resistance cold across the heater pins (Honda wideband typical 2 to 4 ohms; out-of-spec means kill the sensor).
  4. The expensive misdiagnosis is throwing a $200 to $300 OE Denso AFR sensor at the car when the actual fault is a $40 main relay or a corroded fuse-box terminal that drops voltage under load.
Vehicle-specific patternsHonda Civic D17A and R18 (2001-2011) sees P1166 frequently from PGM-FI main relay degradation.
  • 2001-2011Honda Civic D17A and R18 sees P1166 frequently from PGM-FI main relay degradation.
  • 2003-2007Honda Accord K24A4/A8 sets P1166 from a corroded under-hood fuse box where the AFR heater feed terminal greens over from road-salt intrusion.
  • 2005-2010Honda Odyssey J35 V6 sees P1166 commonly from sensor pigtail damage where the harness routes near the exhaust manifold heat shield.
  • 2007-2011Honda CR-V K24Z typically sets P1166 from a failing heater element inside the sensor itself by 130k to 160k miles.

Estimated repair$30 to $440.

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