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OBD-II Code

P0AFC

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)

$280–$2,200

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

$280 (sensor + bleed) to $850 (inverter coolant pump on Prius) to $2,200 (battery chiller component on Volt/Bolt outside recall).

P0AFC sets when the BMS sees the hybrid/EV battery system coolant temperature sensor "B" reporting a value outside its expected range — either electrically out of range or implausible relative to ambient and pack temperature inputs.

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 procedureP0AFC sets when the BMS sees the hybrid/EV battery system coolant temperature sensor "B" reporting a value outside its expected range — either electr…

P0AFC sets when the BMS sees the hybrid/EV battery system coolant temperature sensor "B" reporting a value outside its expected range — either electrically out of range or implausible relative to ambient and pack temperature inputs. Hybrid/EV battery thermal loops are independent from the engine coolant loop on most platforms (Prius has a separate inverter/transaxle loop; Volt and Bolt have dedicated battery chiller loops with refrigerant tie-in).

The cheapest-first ladder

  1. scan-tool the battery coolant temp "A" and "B" inputs and compare.
  2. After a cold soak overnight, both should read within 5-10 F of ambient and within a few degrees of each other.
  3. Normal pack-thermal-loop operating temp is 60-150 F (Prius inverter loop targets 105-130 F under load; Bolt battery chiller holds the pack at 70-95 F via active refrigerant cooling).
  4. If sensor B reads pinned high or pinned low while sensor A reads normally, the sensor or its harness is the fault — backprobe the signal wire and check resistance (typical NTC: ~3000 ohms at 70 F dropping to ~300 ohms at 200 F).
  5. If both sensors agree but disagree with ambient on a cold soak, you've got a coolant-flow problem (failed coolant pump, blocked loop, low coolant in the auxiliary reservoir).
  6. DO NOT probe HV orange-wire circuits with a standard multimeter.
  7. Always service HV with Class 0 1000V gloves, isolation tester (Megger), and DC-rated lugged probes.
Vehicle-specific patterns2004-2015 Toyota Prius (Gen2/Gen3) throws P0AFC from the inverter coolant loop sensor on the transaxle — the small auxiliary pump (Aisin) that circul…
  • 2004-2015Toyota Prius (Gen2/Gen3) throws P0AFC from the inverter coolant loop sensor on the transaxle — the small auxiliary pump (Aisin) that circulates inverter coolant fails at 100-150K mi and the sensor reports a stuck-temp condition because flow has stopped. Replace the pump and bleed the loop.
  • 2011-2015Chevy Volt Gen1 throws P0AFC from the battery thermal loop sensor — the Volt's pack-chiller plate uses dedicated coolant and the sensor sits at the chiller outlet; a failed sensor or a low refrigerant charge upstream (the chiller ties into the A/C system) sets P0AFC.
  • 2017-2019Bolt EV throws P0AFC from the battery thermal management circuit; the Bolt's pack has multiple temperature inputs and sensor B specifically is on the lower cooling plate.
  • 2016-2022Mercedes EQ-class plug-in hybrids (S550e, GLC350e) throw P0AFC from coolant pump failure on the HV battery loop — the Bosch auxiliary pump has a known wear pattern.

Estimated repair$280 (sensor + bleed) to $850 (inverter coolant pump on Prius) to $2,200 (battery chiller component on Volt/Bolt outside recall).

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