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DTC codes / P0Axx · Hybrid propulsion / P0AC5

P0AC5Hybrid/EV Battery Temperature Sensor B Circuit

P0AC5 indicates that the hybrid or electric vehicle battery pack's temperature sensor B circuit is reporting a voltage outside the range the battery energy control module expects, which prevents accurate thermal monitoring of the high-voltage pack. The computer has detected an abnormal signal on that sensor's circuit, either an open, a short, or a value that does not track with the other temperature sensors.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaHybrid propulsion

Symptoms you may notice

  • Illumination of the hybrid system warning light or service vehicle soon message, often with no other noticeable symptoms
  • Reduced electric-only driving range or a forced switch to gasoline engine operation in a plug-in hybrid
  • A sudden drop in available battery power or a limp-home mode that limits vehicle speed
  • Failure of the high-voltage battery to accept a charge or premature termination of a charging session
  • Inconsistent state-of-charge readings or a battery gauge that behaves erratically
  • In rare cases, a message advising the vehicle be parked and serviced due to a high-voltage battery fault

Common causes, most likely first

  1. A failed battery temperature sensor B inside the high-voltage pack, either open circuit or out of calibration
  2. Corroded, loose, or damaged wiring or connector pins in the sensor harness between the pack and the control module
  3. A short to ground or short to voltage on the sensor signal or return circuit
  4. A faulty battery energy control module or hybrid control module that misinterprets a valid sensor signal
  5. Internal battery pack damage or a loose sensor mounting that allows poor thermal contact with the cells
  6. Water intrusion or debris in the battery pack connector causing intermittent signal loss

How to diagnose and fix it

  1. Scan all modules for stored and pending codes, then record freeze-frame data for P0AC5 and any companion temperature sensor codes
  2. Inspect the battery pack wiring harness and connectors for corrosion, chafing, or pushed-out pins, especially at the pack pass-through
  3. Measure the resistance of sensor B at the control module connector and compare it with the other battery temperature sensors at the same ambient temperature
  4. Back-probe the sensor signal circuit and check for a short to ground or short to voltage with the key on and the module disconnected
  5. If the sensor resistance is out of specification or does not change with temperature, replace the affected battery temperature sensor
  6. After repair, clear codes and perform a battery pack temperature sensor learn or adaptation procedure if the manufacturer requires it
  7. Road test and verify that all battery temperature readings track within a few degrees of each other and that P0AC5 does not return

Why sensor B fails without a pack fault

  • A common misdiagnosis is replacing the entire high-voltage battery pack when only one temperature sensor has drifted, so always compare sensor B against the other pack sensors before condemning the pack.
  • Intermittent P0AC5 codes often trace to a connector that is only loose when the pack expands and contracts with temperature, so wiggle-test the harness while watching live data.
  • Some vehicles set P0AC5 when the 12-volt auxiliary battery is weak because the control module logs implausible sensor values during low-voltage cranking, so check the 12-volt system first.
  • A sensor that reads a plausible but fixed temperature, such as always 25 degrees Celsius, indicates an internal short in the thermistor rather than an open circuit, and this distinction changes the repair.
  • Aftermarket battery pack repairs or replacement modules sometimes need a temperature sensor calibration routine that generic scan tools cannot perform, which leaves a false P0AC5 stored.

Can I keep driving with P0AC5?

The vehicle is generally safe to drive short distances because the fault affects monitoring rather than immediate high-voltage safety, but avoid aggressive acceleration, fast charging, and long trips until the circuit is repaired. If the cluster displays a park-immediately message or the battery temperature gauge behaves erratically, stop driving and have the vehicle towed to avoid thermal stress on the pack.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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