P0515

P0515 sets when the ECU/BCM reads the battery temperature sensor (BTS) and the signal is out of range or implausible - the sensor measures battery electrolyte/case temperature so the alternator's commanded charging voltage can be temperature-compensated (cold batteries need higher charge voltage, hot batteries need lower). Vehicles with intelligent charging strategies use the BTS to prevent overcharging in summer and undercharging in winter. Cheapest-first ladder: (1) Locate the BTS - usually a small thermistor either embedded in the battery tray, clipped to the battery case, or integrated into the negative cable terminal (IBS-style on newer vehicles). (2) DMM the thermistor resistance and compare to ambient - typical NTC behavior is 10k ohms at 25C, dropping to ~3k at 50C and rising to ~30k near 0C; out-of-spec readings confirm sensor failure. (3) Inspect the connector and harness for corrosion - battery acid creep at the negative terminal eats sensor connectors. (4) If the BTS is integrated into an IBS (Intelligent Battery Sensor), the whole IBS unit replaces as an assembly. Expensive-misdiagnosis trap: replacing the alternator on P0515 when the charging voltage is wrong because the BTS is lying about battery temp.

Vehicle-specific patterns: 2012-2018 RAM 1500 / 2500 / 3500 throws P0515 commonly from a failed IBS on the negative battery post - Chrysler issued part-number updates on the IBS. 2008-2014 Dodge Caravan / Chrysler Town & Country with the BTS in the battery tray throws P0515 from corroded connector pins. 2010-2016 Jeep Grand Cherokee / Dodge Durango throws P0515 from a known BTS wiring issue. 2014-2018 Chrysler 200 / Dodge Dart with the IBS sensor throws P0515 from IBS failure that requires module relearn after replacement. Estimated repair: $80 to $300