Code
P1451
ALFA ROMEO
P — Powertrain
Intake air heater control fault
Views:
UK: 2
EN: 4
RU: 6
AI status
Completed
Completed
100%
Causes
- Blown fuse or faulty relay for the intake air heater circuit
- Open, shorted or corroded wiring/connectors between the PCM and heater element
- Failed intake air heater element (open or internally shorted)
- Faulty heater control module/driver inside the PCM
- Poor ground at the heater or ECM ground point
- Intermittent connection due to vibration or water intrusion
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light ON
- Difficult or extended cold starting
- Rough idle or elevated emissions during warm-up
- Longer than normal engine warm-up time
- Possible reduced engine performance until engine reaches operating temperature
What to check
- Read stored freeze-frame and pending codes with a scan tool; note operating conditions when fault set
- Visually inspect fuses and relays for the intake air heater circuit; replace if blown
- Inspect wiring and connectors for corrosion, damage, water ingress and secure connections at the heater and PCM
- Check for proper ground(s) at heater and ECM
- With connector disconnected, measure heater element resistance with an ohmmeter and compare to specification
- With ignition ON (engine off), back-probe power supply terminal at heater connector and confirm battery voltage is present when the circuit is commanded on
Signal parameters
- Heater element resistance (typical): low ohms range — commonly 1–20 Ω (manufacturer-specific)
- Supply voltage (ignition ON): approximately battery voltage 11–14 V at the heater supply terminal
- Control signal: PCM may switch ground or supply (depending on design) and may use PWM; expected switching when commanded
- Current draw when energized: may be in the amp range (often 0.5–10 A) depending on heater design; significantly higher or open circuit indicates fault
- Intake Air Temperature (IAT) sensor voltage/resistance: should be within expected range for ambient temperature
Diagnostic algorithm
- Verify complaint and confirm P1451 is active with a scan tool; record freeze-frame data and relevant sensor values (IAT, battery voltage, engine temp).
- Perform visual inspection: fuses, relays, harness, connectors, and grounds. Repair obvious damage and clean corroded terminals.
- Check fuse/relay: replace fuse if blown; swap relay with identical known-good relay if available.
- Measure heater element resistance at the heater connector (with connector unplugged). Compare to specification. An open or very high value indicates a failed heater element.
- With ignition ON, back-probe the heater supply and control terminals. Verify battery voltage at supply and that the PCM provides switching (ground or supply) when commanding the heater ON via a scan tool.
- If voltage present but heater draws no current, suspect open element or poor ground. If excessive current draw occurs, suspect shorted element or wiring short to ground.
- Probe PCM output with a lab scope or DVOM while commanding the heater to verify PWM or switched output and look for intermittent behavior.
- If wiring and heater check good but PCM output not switching, test/replace PCM or heater control module per manufacturer guidance.
- After repair, clear codes and perform several cold-start cycles to confirm the fault does not return and system operates normally.
Likely causes
- Blown fuse or faulty relay
- Open or corroded connector/wiring at the heater element
- Failed heater element
Fault status
Status
Intake air heater control circuit fault detected by PCM — check heater element, wiring, fuses/relays and PCM output.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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