P058C: Battery Monitor Module Temperature Monitoring Performance
What to do
If this car has been through several batteries in a few years, mention it. This sensor decides how the battery is charged, and a wrong reading quietly ruins batteries over months — so the answer may be this sensor rather than another new battery.
Say whether the battery has been changed recently, and whether the sensor clamp was refitted and tightened properly. It sits in the negative terminal clamp and a poor joint there affects everything it measures.
Ask for it to be checked from cold, ideally after the car has stood overnight, since that is when every temperature sensor should agree.
Expect stop-start to be disabled, which is the system being cautious rather than a second fault.
What this code means
The battery monitoring sensor's temperature measurement is not behaving credibly.
Temperature is not a side feature of a battery monitor — it is central to the calculation it exists to make. A battery's capacity, its internal resistance and the voltage it should be charged to all change substantially with temperature. A cold battery accepts charge poorly and needs a higher charging voltage; a hot one needs less, or it gasses and ages.
So the state-of-charge figure the module reports is temperature-corrected, and a wrong temperature makes that figure wrong without anything looking broken.
The consequences are slow and expensive rather than sudden. Undercharging sulphates a battery over months; overcharging cooks it. Either way the failure arrives later, looks like an ordinary flat battery, and gets a new battery fitted — which then does the same thing.
A car on its third battery in a few years is worth checking here rather than buying a fourth.
Range/performance is caught by comparison, and the cold soak is decisive: after standing overnight, this sensor should read close to ambient and close to every other temperature sensor on the vehicle.
Check the clamp connection before the sensor. The monitor sits in the battery's negative terminal clamp, so a poor joint there — corrosion, or a clamp not tightened after a battery change — affects everything it measures.
Likely causes
Start here
- Faulty battery monitoring sensor · moderate
- Corroded or loose connector · easy
Less common
- New battery not registered to the vehicle · specialist
- High resistance in sensor wiring · moderate
- Sensor drifted out of calibration · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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