Code
B2801
MITSUBISHI
B — Body
Power voltage too high
Views:
UK: 26
EN: 46
RU: 25
AI status
Completed
Completed
100%
Causes
- Faulty alternator voltage regulator (overcharging)
- Stuck or shorted regulator control (field) circuit
- Aftermarket charging or charging-system modification
- Poor or corroded ground or battery connections causing false readings
- Faulty battery causing improper charging behavior
- Open or shorted wiring/connectors to the control module power input
Symptoms
- Battery/charging system warning lamp or message
- Headlights and dash lamps abnormally bright
- Erratic instrument cluster or electronic subsystem behavior
- Blown fuses or damage to sensitive modules
- Stored B2801 (overvoltage) and possibly other related DTCs
- Intermittent starting or accessory operation problems
What to check
- Scan for DTCs and record freeze-frame data (battery/charging voltage at fault time)
- Visually inspect battery, cable terminals and engine/chassis grounds for corrosion or looseness
- Measure battery voltage with engine off (resting) and with engine running at idle and ~2000 rpm
- Measure alternator output and voltage regulator control signals at the alternator (field/brush/plug) with a multimeter or scope
- Check for excessive voltage ripple or spikes (use oscilloscope if available)
- Inspect harness and connectors between alternator and main fuse/ECU for damage or short to battery
Signal parameters
- Battery/rest voltage (engine off): ~12.4–12.8 V expected
- Charging voltage (engine running, idle): nominal 13.5–14.8 V
- Overvoltage trigger range (typical): >15.5–17.0 V (manufacturer-specific)
- Voltage under load/at revs (2000 rpm): should remain within charging spec, not exceed trigger
- Voltage ripple (alternator AC content): typically
- Regulator control signal (PWM duty or field): varies by design — check manufacturer spec
Diagnostic algorithm
- Read and record all stored codes and freeze-frame data with a scan tool. Note the recorded system voltage.
- Visually inspect battery, main fusible links, cables and engine/chassis grounds. Clean and tighten any suspect connections.
- Measure battery voltage with engine off. Start engine and measure voltage at battery positive/negative at idle and at ~2000 rpm. If voltage >15.5 V, an overcharging condition is present.
- With a multimeter or oscilloscope, measure alternator output at the alternator B+ terminal and check voltage ripple. Excessive ripple or high DC indicates alternator/rectifier problems.
- Inspect and backprobe regulator/field control connector for proper signals. Check for short to battery or stuck control circuit.
- If alternator output is high, isolate alternator: (safely) disconnect alternator connector and re-measure system voltage — if voltage falls to battery resting voltage, suspect alternator/regulator. If voltage remains high, suspect wiring or another power source.
- Check supply/reference voltages to the affected control module(s). If module supply is above spec, trace wiring to source and repair short or replace faulty module as needed.
- Repair or replace faulty alternator, regulator, wiring, or control module as indicated. Clear codes and road test to confirm repair. Re-scan after a drive cycle to ensure code does not return.
Likely causes
- Internal alternator voltage regulator failure producing >15.5–17V output
- Short in regulator control (stator/field) or generator harness
- Battery positive sensing circuit shorted to a higher potential
- Loose/poor ground at engine or chassis causing voltage spikes
- Faulty body/control module power supply or internal regulator
Fault status
Status
Detected power supply voltage above allowable threshold — overvoltage condition reported by control module.
Repair difficulty: Medium
Diagnostic time: 0.5 - 2 hours
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