P058B
Battery Monitor Module Current Monitoring Performance.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 5
- AreaVehicle speed, idle control and auxiliary inputs
- 8B
- FaultThe specific fault in that area
What it means
P058B is a generic code meaning the battery monitor module's current monitoring is not performing as expected. The control unit compared the battery current reading with what it expected, or with other data such as charging output and load, and found it implausible, stuck or out of range. The exact monitoring method and the location of the module or sensor vary by make and model.
Symptoms
- Battery or charging warning light on the dashboard
- Engine management light on
- Stop-start system disabled or not working
- Flat or weak battery, or slow cranking
- Erratic charging behaviour, or electrical features limited to save power
- Incorrect battery state-of-charge display on some models
Possible causes
- Poor connection or corrosion at the battery terminals or battery monitor module/current sensor clamplikely
- Damaged wiring, loose connector or water ingress in the monitor module circuit (power, earth, or data/LIN line)likely
- Faulty battery monitor module or current sensor giving an implausible or fixed readinglikely
- Weak or failing battery causing readings the module judges out of expectationpossible
- Charging system fault such as a failing alternator or regulator, giving charge current that does not match the monitored valuepossible
- Extra accessory or aftermarket equipment wired directly to the battery, bypassing the current sensorpossible
- Software fault or outdated calibration in the engine or power management control unit, where the manufacturer has issued a fixrare
How to diagnose
- Read all stored and pending codes with freeze frame data, and note any related charging, communication or battery codes.
- Visually inspect the battery terminals, earth strap and monitor module or sensor clamp for corrosion, looseness or damage.
- Check the battery's condition and state of charge, and load test it if it is suspect.
- Check the charging output at the battery with the engine running at idle and with a raised load, against the manufacturer's specification.
- Inspect the module's wiring and connector for chafing, pin damage, water ingress and poor terminal tension.
- Check the module's supply, earth and communication signal as per the model's wiring diagram.
- Look for non-standard accessories connected to the battery or earth point that bypass the current sensor.
- Compare live battery current and voltage data with a calibrated current clamp, and check for any manufacturer software updates or bulletins for the model.
How to fix
- Clean and securely refit the battery terminals, earth connections and monitor module clamp, tightening to specification.
- Repair or replace damaged wiring and connectors in the monitor module circuit.
- Replace the battery monitor module or current sensor if it is confirmed faulty, and carry out any required adaptation or registration for the model.
- Replace a weak battery and register it to the vehicle if the manufacturer requires this.
- Repair or replace the alternator or regulator if charging output is out of specification.
- Reroute accessory feeds so they pass through the current sensor correctly, and apply a manufacturer software update if one is relevant.
Can I keep driving?
The car can usually be driven short-term, but the battery may not charge properly and stop-start or other electrical features may be limited. Get it checked soon, as a charging or battery fault could leave you stranded.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.