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Home / DTC / B1100 — PTC heater3 short

B1100 — PTC heater3 short

Detailed page for trouble code B1100.

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Code

B1100

MITSUBISHI B — Body

PTC heater3 short

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

Causes

  • Internal short or failure of the PTC heater element (heater 3)
  • Shorted wiring harness (insulation damage) to ground or battery voltage
  • Corroded, melted, or loose connector at the heater or harness
  • Blown fuse or tripped circuit protection due to overcurrent
  • Faulty HVAC control module / heater driver (open/shorted MOSFET)
  • Water intrusion or contamination in heater assembly or connector

Symptoms

  • Loss of supplemental electric heating (reduced cabin heat)
  • HVAC system displays fault or reduced function for heater circuit 3
  • DTC B1100 stored and possibly an indicator/warning present
  • Blown fuse or repeated fuse failure for the PTC heater circuit
  • Possible burning smell near heater or harness if severe short
  • High current draw on battery or charging system symptoms in severe cases

What to check

  • Read and record stored DTCs and freeze-frame data with scan tool; clear codes and see if B1100 returns
  • Visual inspection of PTC heater assembly 3, connector, and wiring for damage, melting, corrosion, or water
  • Check fuse(s) and circuit breakers related to PTC heater 3 for continuity
  • Backprobe heater 3 connector and measure voltage at key ON/HEAT command
  • Measure resistance/continuity of the PTC heater element with connector disconnected
  • Check for continuity from heater power/conductor to chassis ground (short to ground)

Signal parameters

  • Supply voltage to heater circuit: nominal battery/ignition 12V (verify with meter during command)
  • PTC element resistance: low when cold and increases as element heats (expect rising resistance behavior rather than fixed low ohms)
  • When commanded ON, control module may apply PWM or switched 12V to heater output — verify expected voltage duty
  • Excessive current or near-short to ground will cause fuse opening or very low measured resistance to ground
  • If driver transistor inside HVAC module is failed short, the output may show near battery voltage with no proper control

Diagnostic algorithm

  1. Connect a diagnostic scanner, confirm B1100 and related codes. Note freeze-frame and current status.
  2. Perform a thorough visual inspection of PTC heater 3, its connector, and wiring harness. Look for heat damage, chafing, pin corrosion, or water ingress.
  3. Verify fuses and circuit protection for the PTC heater circuit. Replace blown fuse only after confirming and fixing short condition.
  4. With ignition OFF, disconnect PTC heater 3 connector. Measure resistance from heater pin(s) to ground and between heater terminals. A near-zero resistance to ground indicates a short.
  5. Reconnect and command heater ON with a scan tool while measuring voltage at the connector. If voltage is present but heater does not operate, suspect open/heater fault. If voltage is low or circuit trips, suspect short or driver fault.
  6. If available, measure current draw (clamp meter) during command. Excessive current indicates short or internal heater failure.
  7. If short is confirmed in wiring, isolate section by section (disconnect harness branches) until short location is found. Repair or replace damaged wiring/connector.
  8. If heater element is faulty (internal short or abnormal resistance behavior), replace the PTC heater assembly.
  9. If wiring and heater element are good but the short persists, test/replace the HVAC control module or its driver output following manufacturer procedures.
  10. After repair, clear codes, verify correct operation of heater 3, and perform road/self-test to ensure code does not return.

Likely causes

  • PTC heater element internally shorted or degraded
  • Wiring damaged and shorted to chassis ground
  • Connector pins corroded, melted or contacting body metal
  • Fuse blown indicating overcurrent in heater circuit
  • Heater driver output in HVAC control module failed short

Fault status

⚠️ Status
Electrical short detected in PTC Heater 3 circuit. Possible short to ground or internal heater failure. Circuit may be drawing excessive current and should be inspected and repaired before further use.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.5 hours

Similar codes

B1101 B1102 B1103 B1104 B1110
406

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