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Home / DTC / B1728 — Supply voltage(undervoltage)

B1728 — Supply voltage(undervoltage)

Detailed page for trouble code B1728.

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Code

B1728

MITSUBISHI B — Body

Supply voltage(undervoltage)

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

Causes

  • Weak or discharged battery
  • Poor battery negative or positive terminal connection (corrosion, loose)
  • Blown fuse or fusible link on the module supply circuit
  • Faulty alternator or charging system (no or low charge)
  • Damaged wiring, chafed harness or connector corrosion on the supply or ground circuits
  • High-resistance ground(s) at chassis or engine block

Symptoms

  • Malfunction indicator lamps or warning messages related to systems controlled by the module
  • Intermittent or permanent loss of functions controlled by the affected module
  • Difficulty starting or cranking with low battery voltage
  • Erratic module behavior, resets, or communication errors on scan tool
  • Additional DTCs related to low system voltage or communications

What to check

  • Visually inspect battery terminals and cables for corrosion, damage, or loose connections
  • Measure battery resting voltage (key off) — normally ~12.4–12.8 V for a charged battery
  • Perform cranking voltage check (during starter engagement) — should normally stay above ~9.5 V
  • Start engine and measure charging voltage at battery — should be ~13.5–14.8 V
  • Inspect and test fuses/fusible links and fuse holders for continuity and high resistance
  • Inspect harness and connector at the affected module for corrosion, bent pins, water ingress or damage

Signal parameters

  • Nominal battery (rest): ~12.4–12.8 V (fully charged ~12.6 V)
  • Cranking voltage expected: typically >9.5 V during starter engagement
  • Charging system (running) voltage: 13.5–14.8 V
  • Undervoltage detection threshold (typical): module may flag undervoltage below ~9–10 V or when voltage dips persistently below expected operating range
  • Transient dips under heavy load may be allowed briefly; repeated/prolonged low values are problematic

Diagnostic algorithm

  1. Read freeze frame/confirm when code set (key on, cranking, running) and note related codes. Do not clear immediately. 2) Visually inspect battery, terminals, cables, and ground straps. Clean and tighten as required. 3) Measure battery resting voltage. If below ~12.2 V, charge battery fully and perform load/crank tests. 4) With a DVOM, measure voltage at battery positive and negative during cranking and with engine running; record values. 5) Inspect and test the alternator/charging system output; verify regulator function and belt condition. 6) Check continuity and resistance of fusible links, fuses and their holders supplying the module; replace if high resistance or open. 7) Probe the module supply pin(s) at the module connector with ignition ON and during cranking/running; compare to battery voltage to locate voltage drop points. 8) Wiggle test harness and connectors while monitoring voltage to detect intermittent connections. 9) Inspect chassis/engine grounds and repair/clean connections; measure ground resistance to battery negative. 10) If wiring and power/ground are good and voltage at the module is within expected range but the code persists, consider module internal fault — consult manufacturer data and consider replacement or bench testing. 11) After repairs, clear codes, verify system operation, and perform a road test to confirm code does not return.

Likely causes

  • Battery state of charge low or battery near end of life
  • Loose/corroded battery terminals or poor ground strap connection
  • Fusible link/fuse supplying the module opened or high resistance in fuse holder
  • Open/shorted wiring between battery/ignition and the module harness connector
  • Alternator failing to maintain charge at idle or under load

Fault status

⚠️ Status
Module detected supply voltage below acceptable threshold (undervoltage) on its power input.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0562 P0563 U0100 U0121
406

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Code

B1728

Other B — Body

Seat Driver Rear Up Switch Circuit Short To Ground

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

Causes

  • Weak or discharged battery
  • Poor battery negative or positive terminal connection (corrosion, loose)
  • Blown fuse or fusible link on the module supply circuit
  • Faulty alternator or charging system (no or low charge)
  • Damaged wiring, chafed harness or connector corrosion on the supply or ground circuits
  • High-resistance ground(s) at chassis or engine block

Symptoms

  • Malfunction indicator lamps or warning messages related to systems controlled by the module
  • Intermittent or permanent loss of functions controlled by the affected module
  • Difficulty starting or cranking with low battery voltage
  • Erratic module behavior, resets, or communication errors on scan tool
  • Additional DTCs related to low system voltage or communications

What to check

  • Visually inspect battery terminals and cables for corrosion, damage, or loose connections
  • Measure battery resting voltage (key off) — normally ~12.4–12.8 V for a charged battery
  • Perform cranking voltage check (during starter engagement) — should normally stay above ~9.5 V
  • Start engine and measure charging voltage at battery — should be ~13.5–14.8 V
  • Inspect and test fuses/fusible links and fuse holders for continuity and high resistance
  • Inspect harness and connector at the affected module for corrosion, bent pins, water ingress or damage

Signal parameters

  • Nominal battery (rest): ~12.4–12.8 V (fully charged ~12.6 V)
  • Cranking voltage expected: typically >9.5 V during starter engagement
  • Charging system (running) voltage: 13.5–14.8 V
  • Undervoltage detection threshold (typical): module may flag undervoltage below ~9–10 V or when voltage dips persistently below expected operating range
  • Transient dips under heavy load may be allowed briefly; repeated/prolonged low values are problematic

Diagnostic algorithm

  1. Read freeze frame/confirm when code set (key on, cranking, running) and note related codes. Do not clear immediately. 2) Visually inspect battery, terminals, cables, and ground straps. Clean and tighten as required. 3) Measure battery resting voltage. If below ~12.2 V, charge battery fully and perform load/crank tests. 4) With a DVOM, measure voltage at battery positive and negative during cranking and with engine running; record values. 5) Inspect and test the alternator/charging system output; verify regulator function and belt condition. 6) Check continuity and resistance of fusible links, fuses and their holders supplying the module; replace if high resistance or open. 7) Probe the module supply pin(s) at the module connector with ignition ON and during cranking/running; compare to battery voltage to locate voltage drop points. 8) Wiggle test harness and connectors while monitoring voltage to detect intermittent connections. 9) Inspect chassis/engine grounds and repair/clean connections; measure ground resistance to battery negative. 10) If wiring and power/ground are good and voltage at the module is within expected range but the code persists, consider module internal fault — consult manufacturer data and consider replacement or bench testing. 11) After repairs, clear codes, verify system operation, and perform a road test to confirm code does not return.

Likely causes

  • Battery state of charge low or battery near end of life
  • Loose/corroded battery terminals or poor ground strap connection
  • Fusible link/fuse supplying the module opened or high resistance in fuse holder
  • Open/shorted wiring between battery/ignition and the module harness connector
  • Alternator failing to maintain charge at idle or under load

Fault status

⚠️ Status
Module detected supply voltage below acceptable threshold (undervoltage) on its power input.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

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