P04FF

Code

Generic P — Powertrain

Catalyst Heater Circuit Performance Bank 2

Brand: Generic

Type: P — Powertrain

Views: UK: 22 EN: 26 RU: 29

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Page language: EN

Causes

Open or short in heater wiring between ECM and catalyst/heated oxygen sensor
Failed catalyst heater or heated oxygen sensor (internal heater open or shorted)
Blown fuse or faulty relay supplying heater circuit
Poor connector pins or corrosion at sensor/ECM connectors
Faulty ECM output driver (internal to control module)
Incorrect or incomplete previous repairs or aftermarket modifications

Symptoms

Check Engine lamp (MIL) illuminated
Possible elevated emissions or failed emissions test
Possible poor cold-start emissions control but often no driveability symptoms
Stored diagnostic trouble code and possible reduced on-board readiness for catalyst monitoring

What to check

Read freeze frame and freeze data with a scan tool; confirm P04FF is current and not historic
Inspect fuses and relays related to heater circuits
Visually inspect wiring and connectors for Bank 2 heater for damage, corrosion, or heat damage
Back-probe connector to measure supply voltage and ground with key on/engine cranking
Measure heater element resistance (ohms) on the sensor/catalyst heater
Wiggle test wiring while monitoring heater circuit voltage/continuity to reproduce intermittent faults

Signal parameters

Battery supply voltage to heater circuit: approx. 11–14 V (key on/engine running) - may be switched or fused
Heater element resistance (typical range): roughly 2–50 ohms depending on sensor/vehicle (consult OEM spec)
Heater current draw: can be up to several amps when energized; measure with clamp meter if needed
ECM control signal: steady 12 V or pulsed/duty-cycle drive depending on design—use oscilloscope or scope function to confirm switching
Open-circuit: infinite resistance; short to ground: near 0 ohms

Diagnostic algorithm

Verify the code with an OBD-II scanner and record freeze-frame/live data for Bank 2 heater circuit.
Inspect related fuses and relays; replace any blown fuse and retest.
With ignition OFF, disconnect the Bank 2 heater connector and measure heater element resistance between heater pins; compare to OEM spec (open = faulty heater).
With ignition ON (engine off), back-probe the supply pin at the heater connector to confirm presence of battery or switched voltage. If no voltage, trace supply back (fuse, relay, splice).
Check ground continuity from sensor/heater ground pin to chassis ground/ECM ground.
With engine running or cranking (as appropriate), use a DVOM or oscilloscope to monitor voltage at heater control pin to see if ECU is commanding the heater (steady or pulsed).
Wiggle harness and connectors while monitoring signal to find intermittent faults. Use a smoke tester if suspecting harness damage in sealed areas.
If wiring and supply are good but heater element out-of-spec, replace the affected heater/oxygen sensor/catalyst heater assembly.
If new sensor still shows fault and wiring is good, suspect ECM output driver; perform OEM-recommended ECM checks before replacement.
Clear codes and perform drive/ready cycle to confirm repair and allow monitors to run.

Likely causes

Damaged wiring harness at flex points or near exhaust heat shield rubbing through insulation
Corroded connector at the heated oxygen sensor or catalyst heater assembly
Heater element failed due to age/overheating
Fused circuit blown (inline fuse or under-hood fuse block)
ECM driver transistor failed (less common)

Fault status

⚠️ Status

Catalyst heater circuit performance fault detected on Bank 2. ECM has determined the heater is not responding or there is an electrical fault in the heater circuit.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

Repair manuals