P0AA3: Hybrid/EV Battery Negative Contactor Circuit

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.

Symptoms

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

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

1. Read the codes with a hybrid-compatible scanner and write down the freeze frame data
2. Make sure the battery cooling air intake is clean
3. Check the 12 V auxiliary battery, which can also trigger warnings
4. Leave any high-voltage measurements to a specialized repair shop

Good to know

• It can trigger limp mode.
• It affects emissions.

What each character of P0AA3 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• A: Hybrid or air and fuel
• A3: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0AA3?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code P0AA3?

The most common causes are: negative contactor or battery junction box worn or damaged; fault in the contactor coil wiring or connector; battery controller driver or software fault.

Related codes

• P0AA4Hybrid/EV Battery Negative Contactor Circuit Stuck Closed
• P0AA5Hybrid/EV Battery Negative Contactor Circuit Stuck Open
• P0AA0Hybrid/EV Battery Positive Contactor Circuit
• P0ADDHybrid/EV Battery Negative Contactor Control Circuit/Open

Sources

• law.cornell.edu: 13 CCR 1968.2
• gsi.ext.gm.com: 19OBDG02 Hybrid Diagnostics
• static.nhtsa.gov: INOA RQ23004 4752

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.