Code
P1403
FIAT
P — Powertrain
Additional heating fault | Auxiliary heater fault
Views:
UK: 4
EN: 6
RU: 8
AI status
Completed
Completed
100%
Causes
- Failed auxiliary/additional heater unit (internal electronics, glow plug or burner)
- Open/short in wiring harness to the heater (power, ground or control signal)
- Blown fuse or faulty relay for the auxiliary heater circuit
- Blocked or failed fuel supply to the heater (pump, valve or clogged line)
- Faulty temperature or exhaust sensors associated with the heater
- Corroded/loose connectors at heater or control module
Symptoms
- Reduced or no auxiliary heating of coolant/cabin when ignition or preheating requested
- Warning light or message for auxiliary heater on dash
- DTC P1403 stored in ECU and possibly other heater-related codes
- Cold engine/cabin in cold-start conditions, extended warm-up time
- Unusual odor of fuel near vehicle, or visible smoke from heater exhaust
- Heater runs briefly then stops, or fails to ignite
What to check
- Retrieve stored DTCs and freeze-frame data with an OBD scan tool; check for additional heater module codes
- Confirm operating conditions (battery voltage, coolant level, ambient temperature) required for heater operation
- Visually inspect heater unit, harness, connectors, fuses and relays for corrosion, damage or loose connections
- Check for correct supply voltage (approx. battery voltage) and a good ground at the heater connector with key-on and heater request
- Inspect fuel supply to the heater: lines, feed pump (if applicable), and filter; check for fuel presence at heater inlet when heater is commanded
- Read heater module live data (status, fault bits, temperature sensors, runtime) using manufacturer-level diagnostic tool if available
Signal parameters
- Power supply: battery voltage present at heater supply terminal when heater is commanded (approx. 12–14 V)
- Control signal: on/off command from vehicle ECU or dedicated heater controller (logic-level ON/OFF or PWM depending on vehicle)
- Ground: low-impedance ground at heater return; open or high-resistance ground will impede operation
- Heater element/igniter resistance: typically low ohms (consult manufacturer's service data)
- Temperature sensor: voltage/resistance changes corresponding to temperature; compare to manufacturer spec
- Current draw: heater should draw expected current when running; abnormally high/low current indicates short/open or internal failure
Diagnostic algorithm
- Read and record all codes and freeze-frame data. Note vehicle conditions when fault occurred.
- Verify vehicle battery state and charge; weak battery can affect heater operation. Check fuses and relays for the auxiliary heater circuit and replace if blown or faulty.
- Perform a visual inspection of the auxiliary heater unit, wiring harness and connectors for damage, corrosion or water ingress; repair as required.
- With the heater requested (via preheat or diagnostic command), measure voltage at the heater power terminal and check for a good ground at the return terminal. If power/ground missing, trace wiring back to fuse/relay/ECU.
- If power and ground are present, use manufacturer diagnostics to read heater module status and fault codes. If unavailable, measure current draw to confirm the heater is attempting to run.
- Check fuel supply to the heater: verify fuel pump (internal or external) operation, inspect lines and filter for blockages or leaks and ensure fuel reaches the heater.
- Inspect heater sensors (coolant temp, exhaust temp, flame sensor) for correct values/resistance. Replace sensors that are out of specification.
- If heater unit fails to operate despite correct wiring, power and fuel, bench-test or replace the auxiliary heater assembly per manufacturer guidance.
- After repairs, clear codes, perform heater activation cycles and verify correct operation and that code does not return.
- If intermittent or communication-related faults persist, check data bus communication to heater/ECU and consider ECU/software updates as per service bulletins.
Likely causes
- Poor or missing power/ground at heater connector
- Faulty auxiliary heater control module or internal failure of heater unit
- Fuel delivery failure to heater (fuel pump within heater or external feed line)
- Defective temperature/exhaust sensor causing heater shut-down
Fault status
Status
Auxiliary/additional heater fault detected — check heater unit, power/ground, fuel supply and control module.
Repair difficulty: Medium
Diagnostic time: 1.5–3.0 hours
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