OBD-II Code
P0A02
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)
$200–$700
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
P0A02 is set when the auxiliary inverter coolant pump (the electric pump that circulates coolant through the inverter, MG1, MG2, and on some platforms the DC-DC converter) fails to maintain commanded flow against the ECU's expected current draw and temperature-rise model.
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 procedureP0A02 is set when the auxiliary inverter coolant pump (the electric pump that circulates coolant through the inverter, MG1, MG2, and on some platform…
P0A02 is set when the auxiliary inverter coolant pump (the electric pump that circulates coolant through the inverter, MG1, MG2, and on some platforms the DC-DC converter) fails to maintain commanded flow against the ECU's expected current draw and temperature-rise model.
The cheapest-first ladder on a shop floor
- pull the freeze-frame data and confirm inverter coolant temp at fault (Toyota HSD sets P0A02 when inverter temp climbs past roughly 150 to 170 F faster than the rate model predicts for the commanded pump duty); scan-tool the pump current draw on the dedicated PWM bus (a healthy aux pump pulls 0.5 to 1.0 A at low duty and 1.8 to 3.0 A at full duty, depending on platform) and watch the duty-cycle command climb to 100% with no corresponding flow response.
- Visual: pop the hood and look for the aux pump (separate from the engine coolant pump, usually mounted near the inverter on the front-left of a Prius); listen for it running and feel the upper inverter hose for warmth and flow pulse.
- Bleed the inverter coolant loop at the dedicated bleed screw before condemning the pump (an air pocket is the #1 false-positive cause), top off with Toyota Super Long Life or platform-equivalent (NEVER mix with conventional green or G12).
- DO NOT probe HV orange-wire circuits with a standard multimeter.
- Always service HV with Class 0 1000V gloves, isolation tester (Megger), and DC-rated lugged probes.
- The HV interlock loop exists specifically to drop pack contactors when the service plug is removed; bypass at lethal risk.
Vehicle-specific patterns2004-2009 Toyota Prius Gen 2 (NHW20) is the textbook P0A02 vehicle and the reason this code is famous; Toyota issued a well-known TSB and an extended…
- 2004-2009Toyota Prius Gen 2 (NHW20) is the textbook P0A02 vehicle and the reason this code is famous; Toyota issued a well-known TSB and an extended warranty on the inverter assembly tied to coolant pump failure, which causes inverter overheat shutdowns on hills and at sustained highway speed; the aux pump is a $150-250 part and a 1-hour job once you bleed the loop.
- 2010-2015Prius Gen 3 (ZVW30) inherited the same aux pump architecture and the same failure mode with slightly improved pump durability; same TSB pattern, same fix.
- 2012-2015Prius Plug-In and 2007-2017 Camry Hybrid / Highlander Hybrid (2AR-FXE and 2GR-FXE) share the inverter cooling design and throw P0A02 from the same root cause.
- 2005-2012Ford Escape Hybrid (eCVT) uses a different aux pump but throws the same code with the same diagnostic ladder.
Estimated repair$200 to $700.
Look up another code
More free tools