OBD-II Code P0517 — What It Means & How to Fix It

What Does This Error Mean?

P0517 means the battery temperature sensor circuit is reading higher than its valid range. For an NTC thermistor sensor, a high-voltage reading means the sensor is indicating an unrealistically low temperature — or the circuit has an open (broken wire or disconnected sensor). The PCM interprets this as the battery being very cold and may increase charging voltage unnecessarily. Overcharging a battery that is actually warm shortens battery life and can cause swelling or leaking.

Affected Models

Vehicles 2000 and newer with temperature-compensated charging systems
Common on GM, Ford, Chrysler, and European vehicles
Hybrid vehicles with 12V auxiliary battery temperature monitoring
Any vehicle where the BCM or PCM monitors battery temperature sensor voltage
Vehicles in very cold climates where the sensor has experienced extreme thermal cycling

Common Causes

Open circuit in the sensor wiring — a broken wire causes the circuit to float high
Battery temperature sensor connector is disconnected, backed out, or has an open pin
Sensor has failed internally with an open element — no longer completing the circuit
Wiring harness between the sensor and the PCM has a break from vibration or physical damage
Battery replacement was done without reconnecting the temperature sensor lead

How to Fix It

Check whether the battery was recently replaced. Battery temperature sensor connectors are commonly left unplugged after battery service. Simply reconnecting the sensor and clearing the code may resolve P0517 completely.

Look for a small connector near the battery that may be dangling unconnected. It is easy to overlook during a battery swap.
Measure resistance across the sensor terminals. An infinite reading (no continuity) confirms the sensor's internal element is open and the sensor has failed.

A properly functioning NTC thermistor will always show a finite resistance value — even at extreme cold temperatures, resistance stays within measurable range.
With the sensor disconnected, probe the harness-side connector for the 5V reference signal with the ignition on. If no voltage is present on the reference wire, the PCM's supply circuit has an open or the PCM itself has an issue.

The 5V reference is supplied by the PCM or BCM — no voltage here means a wiring break between the module and the connector.
Trace the wiring harness for any broken sections, especially at bends, connectors, and routing clips. Use a multimeter set to continuity mode and probe along the wire until you find where continuity is lost.

Battery area wiring can be stretched or broken when the battery is removed and replaced, especially if the wiring was not carefully managed.
Replace the sensor if it is open internally, or repair the broken wiring with a proper soldered splice with heat shrink. Perform a BMS reset if required by your vehicle. Verify the sensor reads a realistic temperature after repair.

After a BMS reset, the PCM immediately begins using the new sensor data — you should see the charging voltage adjust normally within a few minutes of driving.

When to Call a Professional

Open-circuit battery temperature sensor faults are usually simple and inexpensive to repair. The main challenge is finding the break in the wiring. Shops can typically diagnose and fix this within 1 hour.

Frequently Asked Questions

Can an open circuit battery temp sensor overcharge my battery?

Yes. If the sensor circuit reads high (cold indication), the PCM may compensate by raising charging voltage. An overcharged battery generates excess hydrogen gas, heats up, and loses water from its cells. Over time this causes reduced capacity, plate damage, and premature failure. Fix P0517 promptly to protect the battery.

My battery was just replaced — now P0517 appeared. Why?

Almost certainly the technician forgot to reconnect the battery temperature sensor after installing the new battery. The sensor connector is small and easy to miss. Locate the sensor near the battery, reconnect it, clear the code, and the problem is most likely resolved.

How does the PCM decide what charging voltage to use?

The PCM uses a map that correlates battery temperature to optimal charging voltage. At 32°F, the optimal charge voltage is roughly 14.4V to 14.8V. At 100°F, the optimal voltage drops to around 13.5V to 13.8V. Without a valid temperature reading, the PCM either uses a default value or defaults to a fixed charging voltage.