Powertrain, generic · Hybrid propulsion

P0AA3 Hybrid/EV Battery Negative Contactor Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

The negative main contactor switches the negative pole of the traction battery onto the propulsion bus; together with the positive contactor it isolates the pack completely when the car is off. P0AA3 is the general code for this contactor circuit when the fault is not reported more precisely as stuck closed (P0AA4), stuck open (P0AA5) or a control-circuit fault (P0ADD to P0AE0). No manufacturer documents this exact code publicly; GM, Audi, Jeep and Mitsubishi publish the specific siblings. Contact damage from heat and arcing, as described in NHTSA's Mach-E recall query, is the usual background. Expect a hybrid or EV warning and possibly no ready mode; diagnosis belongs to a high-voltage trained workshop.

Likely causes

Negative contactor or battery junction box worn or damaged
Fault in the contactor coil wiring or connector
Battery controller driver or software fault

Symptoms

  • Vehicle does not enter ready mode
  • Hybrid or EV system warning with check engine light
  • Charging may be refused

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–3,000
Time1–6 h

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

Parts involved

hv battery negative contactorwiring harnessbms

Related codes

P0AA4P0AA5P0AA0P0ADD

References: law.cornell.edu, gsi.ext.gm.com, static.nhtsa.gov.