P058A

What it means

P058A means the control unit has judged that the battery monitor module is not performing as expected. The monitor, usually a sensor on the battery negative terminal or a module reporting battery voltage, current, temperature or state of charge, has sent readings that are implausible, out of range or disagree with other data. What it feeds, and what the plausibility test is, depends on the make, model and engine.

Symptoms

• Battery or charging warning light on the dashboard
• Engine management or check engine light on
• Stop-start system not working or disabled
• Slow cranking or flat battery after standing
• Alternator charging seems erratic, or electrical features are limited to save power
• Other stored charging system or communication fault codes

Possible causes

• Loose, corroded or poorly tightened battery terminals, or a poor earth connection at the monitorlikely
• Faulty battery monitor sensor or module, with drifting or implausible readingslikely
• Worn or failing battery giving readings that disagree with the monitorlikely
• Damaged wiring, connector or communication line between the monitor and the control unitpossible
• Charging system fault such as a weak alternator or faulty regulator, causing inconsistent voltagepossible
• Aftermarket accessories or a non-standard battery fitted without the monitor being reset or registered, where the vehicle requires itpossible
• Outdated or faulty control unit software, where a known fault exists for that modelrare

How to diagnose

1. Read all stored codes and freeze frame data, and note any related charging, communication or low voltage codes
2. Inspect the battery terminals, earth straps and the monitor connector for corrosion, looseness, damage or water ingress
3. Measure the battery resting voltage and check the charging voltage with the engine running, to compare against the manufacturer's specification
4. Load test the battery and check its age and condition, since a weak battery can cause implausible readings
5. Check live data for battery voltage, current and state of charge from the monitor and compare with measured values
6. Check the wiring and communication line between the monitor and control unit for continuity, shorts and voltage drop
7. Check the monitor's power supply and earth under load
8. Check for software updates or technical bulletins for the specific model and engine

How to fix

• Clean and tighten the battery terminals and earth connections, and repair any corroded or damaged connectors
• Replace the battery if it fails testing, and register or reset it with the vehicle if the model requires that
• Replace the battery monitor sensor or module if live data is implausible and the wiring checks out
• Repair or replace damaged wiring or connectors in the monitor circuit
• Repair or replace the alternator or regulator if charging output is outside specification
• Apply a manufacturer software update only where a known fault with the existing calibration is documented for that model

Can I keep driving?

Nearby codes

• P0589GenericCruise Control Multi-Function Input B Circuit
• P058BGenericBattery Monitor Module Current Monitoring Performance