Powertrain, generic · Hybrid propulsion

P0A9F Hybrid/EV Battery Temperature Sensor A Circuit Intermittent/Erratic

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Cell temperature changes slowly, so a reading that jumps back and forth points to the circuit, not the battery. GM monitors this by summing the absolute sample-to-sample change of sensor A over a 10-sample window every 100 ms; if the sum exceeds 10, that window fails, and four failed windows out of five set P0A9F as Type B (two trips) in the 2016 and 2019 hybrid tables (16OBDG02, 19OBDG02). GM names a loose or intermittent connection as the typical trigger. The signal may still sit inside its valid range, which separates P0A9F from the hard low/high codes P0A9D/P0A9E and from the plausibility code P0A9C. The car protects the pack by limiting power and may show the fault only now and then.

Likely causes

Loose, fretted or corroded pin in the sensor connector
Partly broken sensor wire that opens with vibration or heat
Electrical interference on the sensor line from high-voltage components

Symptoms

  • Warning light that comes and goes
  • Temporarily reduced hybrid or EV power
  • Battery temperature value jumps in the scan tool data

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–2,000
Time1–5 h

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

Parts involved

hybrid battery temp sensor awiring harnessbms

Related codes

P0A9BP0A9CP0A9DP0A9EP0AC9

References: gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.