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Home / DTC / B1591 — B/UP capacitor capacitance small

B1591 — B/UP capacitor capacitance small

Detailed page for trouble code B1591.

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11,841generic
22,491specific
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Code

B1591

MITSUBISHI B — Body

B/UP capacitor capacitance small

Brand: MITSUBISHI
Type: B — Body
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Page language: EN

Causes

  • Aging or degraded capacitor (electrolytic/solid) with reduced capacitance
  • Overheating or physical damage to the capacitor or PCB
  • Poor electrical connection at capacitor terminals or connector corrosion
  • Faulty charging/resistor circuitry that does not charge the capacitor correctly
  • Blown fuse or open circuit in backup power feed
  • Low or weak vehicle battery preventing proper charging of the capacitor

Symptoms

  • Loss of clock, radio presets, seat/mirror memory or other retained settings after ignition cycle
  • Intermittent or permanent reset of body control or convenience features
  • Related B-codes stored in body/electronics control modules
  • Accessory functions behave unpredictably after engine shutoff or battery disconnect
  • In rare cases immobilizer or anti-theft settings may be affected

What to check

  • Read and record stored DTCs from body and related modules with a compatible scan tool
  • Check vehicle battery voltage and state of charge; ensure battery is fully charged
  • Visually inspect capacitor(s), module and PCB for bulging, leaks, burn marks or corrosion
  • Inspect connectors, wiring harness and fuses in the backup supply circuit
  • Measure capacitance at the capacitor with a capacitance meter (component removed or per service procedure)
  • Measure voltage at capacitor terminals and verify charge/discharge behavior per service manual

Signal parameters

  • Capacitance: must meet manufacturer specification (check service manual for exact µF value)
  • Terminal voltage: should charge to expected voltage when ignition on and hold for specified retention period when ignition off
  • Charge/discharge time constant: consistent with capacitor value and associated resistor/circuit per service data
  • No intermittent open or high resistance at capacitor terminals or connector

Diagnostic algorithm

  1. Verify DTC B1591 is current or stored; record freeze frame and related codes.
  2. Check and confirm vehicle battery voltage is within normal range (fully charged). Recharge or replace battery if low before further testing.
  3. Perform visual inspection of the module, capacitor and nearby components for physical damage, leakage, bulging, heat discoloration or corrosion.
  4. Inspect and wiggle-test connectors and wiring for secure connections; check associated fuses and wiring for continuity.
  5. If accessible, measure capacitance with an LCR or capacitance meter. Compare to service manual specification. If measured in-circuit gives unreliable reading, follow service procedure for safe removal or in-circuit test.
  6. Measure voltage at the capacitor during ignition ON and after key-off to confirm it charges and retains voltage for the expected time. Note any rapid voltage drop.
  7. If capacitor is out of spec, replace the capacitor or the entire module per manufacturer instructions. Use rated replacement parts and respect polarity and safety procedures.
  8. If capacitor measures OK, check charging resistor/circuit and related components (diodes, regulators) for correct operation; repair as needed.
  9. After repair, clear codes and verify proper operation through several ignition cycles. Re-scan for recurrence and re-check retained settings.
  10. If problem persists, consult factory service information or consider module replacement and publishable recalls/TSBs.

Likely causes

  • Capacitor has degraded with age or heat exposure
  • Connector, solder joint or PCB trace corrosion or damage at capacitor
  • Charging resistor or circuit associated with the capacitor is open/failed
  • Vehicle battery low causing insufficient charging of the backup circuit

Fault status

⚠️ Status
Backup capacitor capacitance below specification — memory backup may be unreliable.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B1590 B1592 B1500 B1320 B2550
406

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

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