Code
B1590
MITSUBISHI
B — Body
B/UP capacitor capacitance big
Views:
UK: 11
EN: 12
RU: 13
AI status
Completed
Completed
100%
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
- Connect a scan tool, confirm B1590 and note related codes or freeze data. Do not assume final cause based on code alone.
- Verify battery condition and charging system. A weak or fluctuating battery can produce erroneous readings—repair as needed.
- Perform visual inspection of the body ECU/BCM: look for water damage, corrosion, burnt components, or loose connectors. Repair wiring/connectors as required.
- 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.
- 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.
- 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.
- 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.
- If wiring and capacitor are good, suspect internal ECU measurement circuitry fault. Consider ECU repair/replacement or consult manufacturer technical service information.
- 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.
- 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
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Code
B1590
Other
B — Body
Autolamp Delay Increase Circuit Short To Ground
Views:
UK: 14
EN: 31
RU: 21
AI status
Completed
Completed
100%
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
- Connect a scan tool, confirm B1590 and note related codes or freeze data. Do not assume final cause based on code alone.
- Verify battery condition and charging system. A weak or fluctuating battery can produce erroneous readings—repair as needed.
- Perform visual inspection of the body ECU/BCM: look for water damage, corrosion, burnt components, or loose connectors. Repair wiring/connectors as required.
- 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.
- 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.
- 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.
- 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.
- If wiring and capacitor are good, suspect internal ECU measurement circuitry fault. Consider ECU repair/replacement or consult manufacturer technical service information.
- 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.
- 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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