Low voltage means the battery is cold, right?

It is the other way round, and this trips up a lot of people. These sensors are negative-coefficient thermistors — resistance drops as temperature rises. Wired against a pull-up in the module, falling resistance produces falling signal voltage. So a signal near zero volts is interpreted as a very hot battery, not a cold one, and the charging system responds by lowering its voltage target. That is why the practical consequence of P0516 is chronic undercharging.

Will this code kill my battery?

Not immediately, but left alone it will shorten its life meaningfully. A battery held below its proper charging voltage never returns to full charge, and a lead-acid battery that spends months partially charged develops sulphation on the plates, which permanently reduces capacity. The failure looks like a battery that ages several years in one winter. If your battery is already struggling, plan on replacing it alongside the circuit repair rather than assuming it will recover.

How do I tell whether it is the sensor or the wiring?

Unplug the sensor and watch the live data value. With the connector open, the circuit should go to its opposite extreme — a very cold reading, and often a switch to P0517 on the next check. If that happens, the harness is fine and the sensor was shorting. If the reading stays pinned hot with nothing connected at all, the short is somewhere in the wire between the connector and the module. It is a thirty-second test that decides where the rest of your afternoon goes.

Why does this sensor corrode so much more than others on the car?

Location. It is mounted directly under a lead-acid battery, which is the only component on the vehicle that routinely weeps sulphuric acid onto whatever sits beneath it. That acid does two things at once: it corrodes copper into a conductive green residue that can bridge terminals, and it degrades wire insulation until the conductor touches the grounded metal tray. Both produce the pinned-low signal this code describes. When you have the battery out, clean the tray thoroughly and neutralise any residue, or you will be back.

OBD-II trouble code

P0516: Battery Temperature Sensor Circuit Low

Signal voltage on the battery temperature circuit has collapsed toward zero, which a thermistor circuit reads as "extremely hot" — so the charging system pulls voltage down and quietly undercharges the battery.

Low severityPowertrainCharging / ElectricalDrivable short-term

Quick facts

System: Powertrain
Category: Charging / Electrical
Severity: Low severity
Drivable: Usually safe to drive short-term
Repair cost range: $70 – $350
DIY difficulty: Beginner DIY

What does P0516 mean?

The direction matters here, and it matters in a way that is easy to get backwards. Battery temperature sensors are negative-coefficient thermistors: their resistance falls as they get hotter. Wired as a divider against a pull-up inside the module, low resistance produces low signal voltage. So when the module sees the signal sitting near zero volts — typically below about three tenths of a volt for longer than the calibration tolerates — the value it computes is not "no signal." It is "this battery is extremely hot."

That interpretation drives the whole consequence of P0516. A hot battery must be charged at a lower voltage to keep it from gassing, so the charging strategy responds to the apparent heat by reducing its target. The result is a battery that never receives the voltage it actually needs. In cold weather the effect compounds badly, because a cold battery needs a higher voltage than normal and is instead being given a lower one. Owners describe it as a battery that seems fine in summer and cannot crank in January, or one that goes flat after a week of short trips because each trip returns less charge than it consumed.

Electrically, a signal pinned low means one of three things. The signal wire is shorted to ground somewhere along its route. The thermistor itself has failed shorted internally. Or the module's own input driver has failed, which is the rare case and should be concluded last. Distinguishing the first two takes about a minute: unplug the sensor at its connector and watch the reading. If the value swings to the opposite extreme and the stored code changes to P0517, the wiring back to the module is intact and the sensor was the short. If it stays pinned low with nothing connected, the short is in the harness.

There is one cause this sensor faces that almost no other temperature sensor on the vehicle does, and it deserves to be checked before anything else. The sensor sits directly beneath a lead-acid battery. Batteries seep. Electrolyte creeping down the case runs onto the sensor, its pigtail and its connector, and sulphuric acid does two things at once — it corrodes copper into a green conductive mess and it eats through insulation, exposing conductors to the metal tray beneath. A conductive acid film bridging the signal wire to the grounded tray produces exactly the pinned-low reading this code describes, with a perfectly healthy thermistor still fitted.

Common causes

Signal wire shorted to ground, most often where acid seepage has eaten insulation against the metal battery tray
Electrolyte corrosion bridging the sensor connector terminals with a conductive film
Battery temperature sensor failed shorted internally
Sensor wire pinched between the battery hold-down and the tray during a battery replacement
Chafed harness where it exits the battery tray and passes over a bracket edge
Water intrusion into the sensor connector, which sits at one of the lowest points in the engine bay
Damaged pigtail from a previous battery removal, where the connector was pulled rather than released
Module input circuit failure, uncommon and only after the wiring and sensor have been cleared

Symptoms

Check engine light on with P0516 stored and no change in engine performance
Battery temperature in live data pinned at the top of its scale, often reading well over 100 degrees on a cold engine
Charging voltage measured at the battery lower than normal, frequently around 13.2 to 13.6 volts
Battery going flat after several days of short trips, because each trip returns less than it takes
Slow cranking in cold weather that gets steadily worse over a season
A relatively new battery that tests as discharged rather than as failed
Green or white corrosion visible on the sensor pigtail when the battery is lifted out

Diagnostic steps

1.Read battery temperature in live data with the engine stone cold. A value pinned at the hot end of the scale on a cold morning confirms the direction and tells you the module is genuinely acting on a false hot reading.
2.Unplug the sensor at its connector and watch the live value. Swinging to the cold extreme, or the code changing to P0517, proves the harness back to the module is sound and puts the fault in the sensor. Staying pinned low with nothing plugged in puts it in the wiring.
3.Lift the battery out and inspect everything underneath with a light. You are hunting for acid seepage, white crystalline deposits, green corrosion on the pigtail, and insulation worn through against the tray. On this particular sensor that inspection resolves a large share of cases outright.
4.With the sensor unplugged, measure resistance from the signal terminal on the harness side to a known good ground. A healthy circuit reads effectively open. Anything low confirms the short and tells you to trace the wire rather than order a part.
5.Measure the thermistor's resistance across its own terminals. A shorted sensor reads near zero at any temperature and will not change when you warm it in your hand.
6.Once the circuit is repaired, measure actual charging voltage at the battery posts before and after a cold start. Recovering to a temperature-appropriate value rather than the reduced fallback confirms the fix took effect.

Repair cost

$70 – $350

Cleaning and repairing an acid-corroded connector and pigtail is the most common actual fix and runs $90-$220, more if the corrosion has travelled far enough up the harness to need a section replaced. A shorted sensor is an inexpensive part at $15-$60, giving a total of $70-$180 including the time to lift the battery. Tracing a short to ground in a chafed harness can reach $150-$350 if the damage is buried in a loom. Budget separately for the battery itself: a battery that has been chronically undercharged for months is often permanently sulphated and will need replacing regardless of the circuit repair.

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DIY vs shop

This is a beginner-friendly repair. Common hand tools, a free afternoon, and a willingness to follow a procedure are usually enough. The risk of causing a bigger problem is low if you read up on your specific vehicle first.