Powertrain, generic · Hybrid propulsion

P0A0F Engine Failed to Start

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

The control module commanded an engine start – by the hybrid system or an automatic start/stop restart – but the combustion engine did not reach a self-sustaining run within the allowed attempts. The code describes the result, not the cause. Toyota sets P0A0F with MIL on the 2010-2013 Prius and Prius v when a separated purge VSV/PCV hose leans out the mixture, often with P3190, P3191 and P0171. Kia traced P0A0F on the 2017-2018 Niro hybrid to an A/C pressure sensor harness chafed by an idler pulley, which disturbs the engine ECU 5 V reference. Audi sets P0A0F00 on 2019 A6/A7 3.0 mild hybrids after the second failed automatic restart, with a drive system warning. Look at fuel, air, ignition and engine sensor faults first.

Likely causes

Vacuum leak, e.g. separated purge VSV/PCV hose at the throttle body (Toyota Prius)
Shorted sensor harness pulling down the engine ECU 5 V reference (Kia Niro)
Fuel delivery or ignition fault preventing combustion
Failed automatic restart of a mild hybrid with a cold engine (Audi A6/A7 2019)

Symptoms

  • Check engine light and hybrid or drive system warning
  • Engine does not start, or runs briefly and stops
  • Reduced power because the vehicle runs on the battery only

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–800
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

hybrid control moduleengine starterhv battery

Related codes

P0A1DP0335P0171P0404

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.