Code
P1403
ALFA ROMEO
P — Powertrain
Additional heating fault | Auxiliary heater fault
AI status
Completed
Completed
100%
Causes
- Blown fuse or tripped circuit breaker for auxiliary heater
- Faulty auxiliary heater unit (electric element, burner, or internal control)
- Failed relay or wiring (open, short to ground, short to battery, corroded connector)
- Poor/dirty ground connection at heater or control module
- Faulty temperature or exhaust sensors used by the heater control (e.g., coolant temp, exhaust temp, flame sensor)
- Blocked fuel supply or failed fuel pump (for fuel‑fired heaters)
Symptoms
- Auxiliary heater does not start or stops prematurely
- Reduced or no cabin heating when auxiliary heater is expected to run
- Heater fault/warning lamp or message on dash
- Unusual odors (fuel or burning) or abnormal exhaust from heater outlet
- Increased engine idling or extended warm-up time if heater not operating
- Possible diagnostic trouble codes stored in heater or engine control modules
What to check
- Read fault memory from engine/auxiliary heater control module with a capable scan tool and note freeze frame/live data
- Visual inspection of fuse(s), relays and wiring harness to the heater for damage or corrosion
- Check connector pins for corrosion, water ingress or loose terminals
- Verify battery supply voltage at heater connector with ignition on and during attempted start
- Verify good ground at heater and control module
- Inspect intake/exhaust paths for blockages and check for soot or deposits (fuel heaters)
Signal parameters
- Supply voltage at heater connector: ~12–14 V with ignition on/when commanded
- Ground continuity: near 0 Ω between connector ground and chassis
- Control signal (PWM or switched 12 V) present when heater is commanded on
- Heater current draw: varies by unit—compare measured amperage to manufacturer spec (electric heaters often tens of amps)
- Temperature sensor voltage/resistance: compare coolant/exhaust sensor values to spec when cold/hot
- Flame sensor or ionization probe voltage/polarity when burner running (for diesel/gas heaters)
Diagnostic algorithm
- Retrieve all stored codes and live data from engine and auxiliary heater control modules; record freeze frame data.
- Verify ignition and control conditions required for auxiliary heater activation (ambient temp, engine temp, timer/clock settings).
- Perform visual inspection: fuses, relays, connectors, wiring harness routing, and signs of physical damage or water ingress.
- With a DVOM, check battery voltage at the heater power input and the presence of a switched/control signal when heater is commanded on.
- Check ground integrity: measure resistance from heater ground to chassis; repair any high resistance grounds.
- If fuel‑fired heater, verify fuel supply to the heater (fuel pump operation, fuel line condition, filters) and check for fuel smell or leaks safely.
- Test heater activation with a diagnostic tool (command on) and observe current draw, sensor feedback (temp, flame) and exhaust behavior.
- If electrical supply and control signals are good but heater does not run, remove and bench‑test or replace the auxiliary heater unit per manufacturer instructions.
- If intermittent or communication errors persist, inspect module communication lines (CAN/LIN) and consider software updates or module replacement after confirming wiring.
- Clear codes and perform a function test and road/check-cycle to verify repair.
Likely causes
- No power or ground at heater connector (most common)
- Failed heater control module or internal heater component
- Failed relay or blown fuse protecting the heater circuit
- Sensor feedback (temperature/flame) not present causing system to shut down
- Fuel supply fault for combustion type auxiliary heaters
Fault status
Status
Auxiliary/additional heater malfunction detected. Control unit has stored P1403 indicating the heater failed to operate within expected parameters (power, control, sensors, or internal fault).
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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