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Home / DTC / B1590 — B/UP capacitor capacitance big

B1590 — B/UP capacitor capacitance big

Detailed page for trouble code B1590.

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22,491specific
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Code

B1590

MITSUBISHI B — Body

B/UP capacitor capacitance big

Brand: MITSUBISHI
Type: B — Body
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Failed or out-of-spec backup capacitor on the body ECU/BCM
  • Capacitor replaced previously with incorrect value or polarity
  • Short or leakage to ground causing apparent high capacitance/charging
  • Wiring harness damage, corrosion or poor connector connection in the capacitor/power circuit
  • Water ingress or contamination on the ECU circuit board
  • Internal body ECU/BCM fault (measurement circuit or processor error)

Symptoms

  • Stored B1590 diagnostic trouble code in body ECU/BCM
  • Memory items reset after battery disconnect (clock, radio presets, auto settings)
  • Intermittent or permanent loss of retained functions after ignition off
  • Warning lights or body electrical anomalies related to retained-memory features
  • Possible failure to keep real-time clock or settings when engine is off

What to check

  • Read and record DTCs and freeze-frame data with a compatible scan tool
  • Check vehicle battery voltage and condition; poor battery can affect measurements
  • Visually inspect body ECU/BCM and surrounding area for water ingress, corrosion or damaged connectors
  • Inspect PCB near the backup capacitor for burnt components, corrosion, or visible damage
  • Check connector pins and wiring continuity for shorts to ground or open circuits
  • Measure actual capacitor voltage and (if safe) capacitance with appropriate meter

Signal parameters

  • Battery voltage (expected ~12.0–14.5 V with engine running; >11.5 V with key on)
  • Backup capacitor voltage (measured at capacitor terminals or ECU test point)
  • Capacitance value (µF) compared to manufacturer specification
  • Leakage current or insulation resistance to ground from capacitor (should be high/very low leakage)
  • Charging/discharge time constant of the capacitor (compare to expected behaviour)

Diagnostic algorithm

  1. Connect a scan tool, confirm B1590 and note related codes or freeze data. Do not assume final cause based on code alone.
  2. Verify battery condition and charging system. A weak or fluctuating battery can produce erroneous readings—repair as needed.
  3. Perform visual inspection of the body ECU/BCM: look for water damage, corrosion, burnt components, or loose connectors. Repair wiring/connectors as required.
  4. With battery disconnected and proper ESD precautions, inspect the capacitor area on the ECU PCB for damage. If contamination is present, clean with appropriate electronic cleaner and dry fully.
  5. If safe and qualified to do so, measure the capacitor capacitance and leakage with a suitable LCR meter after removing/discharging the capacitor. Compare measured µF and leakage to manufacturer specification.
  6. If capacitor measures out of spec (excessive capacitance, leakage, or short), replace with OEM-specified capacitor (value, voltage rating and polarity). If capacitor was previously replaced, verify correct part and orientation.
  7. If capacitor is within spec, inspect and test wiring harness and connectors for short to ground or intermittent connections. Repair or replace wiring as necessary.
  8. If wiring and capacitor are good, suspect internal ECU measurement circuitry fault. Consider ECU repair/replacement or consult manufacturer technical service information.
  9. After repairs, clear DTCs with scan tool, reconnect battery, cycle ignition and verify code does not return. Confirm retained-memory functions operate normally and re-test under power cycles.
  10. Safety note: Capacitors can retain charge. Always follow safe work practices: isolate battery power, discharge capacitors safely, and use insulated tools and appropriate PPE.

Likely causes

  • Backup capacitor degraded (dielectric breakdown) showing abnormal capacitance or leakage
  • Capacitor fitted with higher capacitance than specified during a prior repair
  • PCB contamination (corrosion or conductive residue) causing leakage paths
  • Connector pins corroded or shorted to chassis ground near the ECU
  • Faulty ECU measurement circuitry misreporting capacitor parameter

Fault status

⚠️ Status
Backup capacitor on body ECU/BCM is showing abnormal capacitance or charging behaviour. May cause loss of retained-memory functions (clock, presets).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B1580 B1591 B1610 B1620
406

Browse 406 MITSUBISHI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

MITSUBISHI

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Code

B1590

Other B — Body

Autolamp Delay Increase Circuit Short To Ground

Brand: Other
Type: B — Body
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Failed or out-of-spec backup capacitor on the body ECU/BCM
  • Capacitor replaced previously with incorrect value or polarity
  • Short or leakage to ground causing apparent high capacitance/charging
  • Wiring harness damage, corrosion or poor connector connection in the capacitor/power circuit
  • Water ingress or contamination on the ECU circuit board
  • Internal body ECU/BCM fault (measurement circuit or processor error)

Symptoms

  • Stored B1590 diagnostic trouble code in body ECU/BCM
  • Memory items reset after battery disconnect (clock, radio presets, auto settings)
  • Intermittent or permanent loss of retained functions after ignition off
  • Warning lights or body electrical anomalies related to retained-memory features
  • Possible failure to keep real-time clock or settings when engine is off

What to check

  • Read and record DTCs and freeze-frame data with a compatible scan tool
  • Check vehicle battery voltage and condition; poor battery can affect measurements
  • Visually inspect body ECU/BCM and surrounding area for water ingress, corrosion or damaged connectors
  • Inspect PCB near the backup capacitor for burnt components, corrosion, or visible damage
  • Check connector pins and wiring continuity for shorts to ground or open circuits
  • Measure actual capacitor voltage and (if safe) capacitance with appropriate meter

Signal parameters

  • Battery voltage (expected ~12.0–14.5 V with engine running; >11.5 V with key on)
  • Backup capacitor voltage (measured at capacitor terminals or ECU test point)
  • Capacitance value (µF) compared to manufacturer specification
  • Leakage current or insulation resistance to ground from capacitor (should be high/very low leakage)
  • Charging/discharge time constant of the capacitor (compare to expected behaviour)

Diagnostic algorithm

  1. Connect a scan tool, confirm B1590 and note related codes or freeze data. Do not assume final cause based on code alone.
  2. Verify battery condition and charging system. A weak or fluctuating battery can produce erroneous readings—repair as needed.
  3. Perform visual inspection of the body ECU/BCM: look for water damage, corrosion, burnt components, or loose connectors. Repair wiring/connectors as required.
  4. With battery disconnected and proper ESD precautions, inspect the capacitor area on the ECU PCB for damage. If contamination is present, clean with appropriate electronic cleaner and dry fully.
  5. If safe and qualified to do so, measure the capacitor capacitance and leakage with a suitable LCR meter after removing/discharging the capacitor. Compare measured µF and leakage to manufacturer specification.
  6. If capacitor measures out of spec (excessive capacitance, leakage, or short), replace with OEM-specified capacitor (value, voltage rating and polarity). If capacitor was previously replaced, verify correct part and orientation.
  7. If capacitor is within spec, inspect and test wiring harness and connectors for short to ground or intermittent connections. Repair or replace wiring as necessary.
  8. If wiring and capacitor are good, suspect internal ECU measurement circuitry fault. Consider ECU repair/replacement or consult manufacturer technical service information.
  9. After repairs, clear DTCs with scan tool, reconnect battery, cycle ignition and verify code does not return. Confirm retained-memory functions operate normally and re-test under power cycles.
  10. Safety note: Capacitors can retain charge. Always follow safe work practices: isolate battery power, discharge capacitors safely, and use insulated tools and appropriate PPE.

Likely causes

  • Backup capacitor degraded (dielectric breakdown) showing abnormal capacitance or leakage
  • Capacitor fitted with higher capacitance than specified during a prior repair
  • PCB contamination (corrosion or conductive residue) causing leakage paths
  • Connector pins corroded or shorted to chassis ground near the ECU
  • Faulty ECU measurement circuitry misreporting capacitor parameter

Fault status

⚠️ Status
Backup capacitor on body ECU/BCM is showing abnormal capacitance or charging behaviour. May cause loss of retained-memory functions (clock, presets).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

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B1580 B1591 B1610 B1620
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