P0A9D: Hybrid/EV Battery Temperature Sensor A Circuit Low

Sensor A is an NTC thermistor fed through a pull-up resistor, so the voltage falls as the temperature rises; a short to ground looks like an absurdly hot cell. GM sets P0A9D (Type B, two trips) when the converted value exceeds 160 °C in 8 of 10 samples (19OBDG02); Two-Mode hybrids use above 95 °C while the other sensors read below 70 °C, other programs above 87.5 °C for 1.4 s. GM's Volt bulletin 18-NA-342 names it sensor 1 circuit low voltage. The low-voltage case is the counterpart of P0A9E (open circuit, reads very cold) and differs from P0A7E, which reports a real overtemperature. Because the controller must assume heat, it cuts charge and discharge power and may run cooling at full speed.

Symptoms

• Check engine or hybrid warning light
• Strongly reduced electric power or no EV mode
• Battery cooling running at high speed without reason

Most likely causes

• Sensor signal wire shorted to ground or chafed inside the pack
• Internally shorted thermistor on the sensing board
• Moisture or coolant in the sensor connector
• Battery controller software causing false sets (GM Volt)

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. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Make sure the battery cooling air intake is clean
4. Check the 12 V auxiliary battery, which can also trigger warnings
5. 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 P0A9D means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• A: Hybrid or air and fuel
• 9D: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0A9D?

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 P0A9D?

The most common causes are: sensor signal wire shorted to ground or chafed inside the pack; internally shorted thermistor on the sensing board; moisture or coolant in the sensor connector.

Related codes

• P0A9EHybrid/EV Battery Temperature Sensor A Circuit High
• P0A9CHybrid/EV Battery Temperature Sensor A Circuit Range/Performance
• P0A9BHybrid/EV Battery Temperature Sensor A Circuit
• P0A7EHybrid/EV Battery Pack Over Temperature
• P0AC7Hybrid/EV Battery Temperature Sensor B Circuit Low

Sources

• gsi.ext.gm.com: 19OBDG02 Hybrid Diagnostics
• gsi.ext.gm.com: 13OBDG06 Hybrid Diagnostics
• static.nhtsa.gov: MC 10155116 9999

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.