P0AA1 The hybrid or EV battery computer sees the positive high-voltage contactor still closed when it should be open

Hybrid battery positive contactor stuck closed

P0AA1 in short

P0AA1 means the hybrid or EV battery computer sees the positive contactor, the high-voltage switch inside the battery, still closed when it should be open. Ford, GM and Chrysler bulletins cover it on Mach-E, Bolt, Malibu Hybrid, Volt and Pacifica. Get it checked soon; stop if a Stop Safely message appears.

A hybrid or EV battery connects to the car through contactors, which are heavy relays. The positive contactor closes to power the car and opens to shut it down. The battery computer checks the voltage past the contactor, and P0AA1 sets when it still sees voltage after it commanded the contactor open, which suggests a contactor that is stuck closed or a circuit that reads wrong.

The fix depends on the maker. Ford bulletin TSB 22-2178 covers 2021-2022 Mustang Mach-E that show Stop Safely Now with P0AA1 and related codes, possibly from the high voltage battery junction box, and replaces the box and reprograms the BECM. GM bulletins cover a disconnect relay replacement on the 2016 Malibu Hybrid and repair information on the 2017-2019 Bolt EV, and a program on the 2019 Volt for a 12-volt battery condition. A Chrysler bulletin covers a BPCM software update on Pacifica.

On a 2007 Saturn Vue hybrid, a GM bulletin says P0AA1 can set in addition to P0A4B and points to a wiring jumper for the starter/generator resolver circuit.

The contactors are part of the high-voltage system. Orange cables and connectors are not for owners to touch. Diagnosis belongs with a dealer or an EV or hybrid trained technician.

Most likely causes

  1. High voltage battery junction box with contactors (Mustang Mach-E)

    Supported by vehicle data
    Why it ranks here
    Ford TSB 22-2178 lists P0AA1 among codes that may come from the high voltage battery junction box and replaces it; owner reports on 2021 and 2024 cars include a dealer diagnosis of the junction box. We read only the bulletin summary.
    What would change this
    Rises on a 2021-2022 Mach-E with a Stop Safely Now message. Falls if the VIN is outside the bulletin range.

  2. Battery disconnect relay or contactor assembly (Malibu Hybrid, Bolt EV)

    Supported by vehicle data
    Why it ranks here
    GM bulletin 18NA084 replaces the disconnect relay (battery contactor assembly) for P0AA1 and P0AA4 with a no-start on the 2016 Malibu Hybrid, and 21NA288 gives repair information for P0AA1 on the 2017-2019 Bolt EV.
    What would change this
    Rises on a covered GM model with a no-start. Falls if the bulletin does not list the VIN.

  3. Battery pack control module software (Chrysler Pacifica)

    Supported by vehicle data
    Why it ranks here
    Chrysler bulletin 08-092-21 lists P0AA1-00 with other battery codes and fixes them with a BPCM software update; complaint ODI 11768274 shows the code on a 2017 Pacifica Hybrid that would not start.
    What would change this
    Rises on a Pacifica with a MIL and several battery codes. Falls if the software is already current.

  4. Low 12-volt battery voltage (Chevrolet Volt)

    Supported by vehicle data
    Why it ranks here
    GM PIC6375 says P0AA1 and P0AA4 can set on the 2019 Volt when 12-volt battery voltage drops below a threshold, and a program repairs it.
    What would change this
    Rises if the 12-volt battery was weak or recently drained. Falls if the 12-volt battery tests healthy.

  5. Starter/generator resolver circuit (2007 Saturn Vue hybrid)

    Possible — needs testing
    Why it ranks here
    A GM bulletin says P0AA1 may set along with P0A4B on the 2007 Vue and installs a harness jumper; it is a different system from the contactor, so it applies only to that model.
    What would change this
    Rises on a 2007 Vue with P0A4B. Falls on any other vehicle.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all stored codes and freeze-frame data with a scan tool and note every dashboard message. Do not open or unplug anything.

    Low riskTool: OBD-II scan tool

    • IfP0AA1 is stored with other battery codes and a Stop Safely or no-start condition

      It meansA dealer should check the high-voltage battery and any open bulletin.

      Go to step 2

    • IfIt is stored on a Mach-E, Bolt, Malibu Hybrid, Volt or Pacifica

      It meansA maker bulletin may apply.

      Go to step 2

    • IfIt is any other vehicle

      It meansThe maker diagnosis decides.

      Go to step 3

  2. Give the VIN to a dealer and ask for open bulletins, recalls and programs for the high-voltage battery, the contactors and the battery control module.

    Low riskTool: VIN lookup at a dealer

  3. Have a dealer or EV or hybrid trained technician check the contactors, the 12-volt supply and the battery computer using the maker service information.

    Best left to a shopTool: factory scan tool and high-voltage safety equipment

    Warning:High voltage: the battery pack, junction box, inverter and orange cables carry hundreds of volts that can kill. Do not unplug, probe or touch them. This work needs a hybrid or EV trained technician who makes the system safe first.

Symptoms

  • Car will not start or go into Ready
  • Stop Safely Now or powertrain malfunction message Gets more serious: stop and have it checked.
  • Loss of power while driving Gets more serious: stop and have it checked.
  • Check engine light with hybrid battery warnings

How to fix

This is a safety-critical system, so we explain the code but don't give repair steps. Have it inspected by a qualified technician.

Parts and cost context

  • High voltage battery junction box or disconnect relay (maker specific):High-voltage part. Check Ford TSB 22-2178 or the GM bulletins for your VIN before paying. Labor varies; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Ford

  • TSB 22-2178Status unverified

    Stop Safely Now with P0AA1 and related codes

    2021–2022mustang-mach-e · issued · NHTSA 10218613

    Replace the high voltage battery junction box and reprogram the BECM.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Chevrolet

  • 21NA288Status unverified

    MIL with P0AA1 on the Bolt EV

    2017–2019bolt-ev · issued · NHTSA 10207924

    Repair information for a MIL with P0AA1, hybrid/EV battery positive contactor circuit stuck closed.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 18NA084Status unverified

    Disconnect relay replacement for P0AA1 and P0AA4

    2016malibu · issued · NHTSA 10137310

    Replaces the high voltage battery disconnect relay (battery contactor assembly) to correct a no-start with P0AA1 and P0AA4.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • PIC6375Status unverified

    P0AA1 and P0AA4 program on the Volt

    2019volt · issued · NHTSA 10168974

    A program repairs these codes, which can set when 12-volt battery voltage drops below a threshold.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Chrysler

  • 2017–2021 · Pacifica

    Supported by vehicle data

    Pacifica Hybrid: Chrysler fixes P0AA1 with other battery codes by BPCM software update.

  • 08-092-21Status unverified

    BPCM diagnostic and system updates

    2021pacifica · issued · NHTSA 10198459

    Software update for a MIL with P0AA1-00 and other battery codes.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Saturn

  • 070603004Status unverified

    Hybrid battery light with P0A4B, P0AA1 may also set

    2007vue · issued · NHTSA 10022479

    Install an engine wiring harness jumper for the starter/generator resolver circuit.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

No curated relationships for P0AA1 yet.

All Hybrid and electric drive codes

P0AA1 questions

Is it safe to drive with P0AA1?

Only if the car drives normally, and only to get it checked. If a Stop Safely message appears, power drops, or the car will not start, stop somewhere safe and arrange a tow.

Can I fix P0AA1 myself?

No. The contactors are inside the high-voltage battery system and need a dealer or a trained technician.

Sources and review

  1. TSB 22-2178: Stop Safely Now with battery codes on the Mach-E — Ford Motor Company ,
  2. NHTSA complaint ODI 11459506: 2021 Ford Mustang Mach-E — NHTSA Office of Defects Investigation
  3. NHTSA complaint ODI 11768274: 2017 Chrysler Pacifica Hybrid — NHTSA Office of Defects Investigation
  4. P0AA1 Hybrid Battery Positive Contactor Circuit Stuck Closed — Troublecodes.net
  5. NHTSA complaint ODI 11655458: 2024 Ford Mustang Mach-E — NHTSA Office of Defects Investigation
  6. 18NA084: high voltage battery disconnect relay replacement — General Motors ,
  7. 21NA288: MIL with P0AA1 on the Bolt EV — General Motors ,
  8. 08-092-21: BPCM diagnostic and system updates (Pacifica) — FCA US ,
  9. PIC6375: P0AA1 and P0AA4 program on the Volt — General Motors ,
  10. 070603004: hybrid battery light with P0A4B on the Vue — General Motors (Saturn) ,
  11. Fault code P0AA1 — TAT scan data library
Last reviewed
Written by
Saurabh K.
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