P04F3

Code

Generic P — Powertrain

Catalyst Heater Supply Voltage Bank 2

Brand: Generic

Type: P — Powertrain

Views: UK: 26 EN: 30 RU: 31

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Page language: EN

Causes

Blown fuse or tripped circuit breaker on heater supply
Open, shorted or damaged wiring or connector in the heater supply or ground circuit (bank 2)
Corroded or loose connector terminals
Faulty catalyst heater element (open or shorted) on bank 2
Faulty relay or supply driver (heater relay)
Defective engine control module (ECM) driver output

Symptoms

Malfunction Indicator Lamp (MIL) illuminated (check engine light)
Reduced or delayed catalytic converter warm-up after cold start
Increased cold-start emissions and possible failed emissions test
Possible poor engine performance during warm-up or rough idle until catalyst reaches temperature

What to check

Read and record freeze-frame and pending data with a capable scan tool; confirm P04F3 active and monitor heater command status
Verify battery voltage and charging system health (battery voltage at rest and when cranking)
Inspect fuses and relays related to heater circuits; replace if blown or suspect
Visually inspect wiring harness and connectors for bank 2 heater for damage, corrosion, heat damage or poor connections
Using a multimeter, measure supply voltage at the heater connector with heater commanded ON and OFF
Measure continuity/resistance of the heater element at the connector (compare to specification if available)

Signal parameters

Expected supply voltage (heater ON): approximately battery voltage (~11–14.5 V) when commanded (vehicle-specific)
Heater OFF: near 0 V supply at heater connector or open-circuit depending on design
Typical heater element resistance: low ohms (vehicle-specific); an open or very high resistance indicates a failed element
Current draw when heater ON: moderate amperage (often 0.5–10 A depending on design) — consult manufacturer values
ECM command status: on/off or PWM duty when warm-up requested (verify with scan tool)

Diagnostic algorithm

Connect a scan tool and confirm the code, freeze-frame and whether the ECM is commanding the bank 2 heater
Verify battery and charging system voltage; charge or repair as needed
Locate related fuses and relays; inspect and test/replace if faulty
With connector accessible, backprobe the heater supply pin and command the heater ON with the scan tool; confirm supply voltage reaches expected battery voltage
Backprobe the heater ground pin and confirm a good ground while heater is commanded ON
Unplug the heater connector at the catalytic heater and measure resistance of the heater element; compare to specification — open or infinite resistance indicates a failed heater
If supply voltage is absent at the heater connector but present at the fuse/relay, trace wiring for open/short and repair; if shorted to ground or power, isolate and repair short
If supply/ground at connector are correct but heater element is within spec and still faults, test ECM driver output for correct switching/PWM; if driver is not switching while commanded, consider ECM or driver circuit fault
Inspect and repair corroded connectors or high-resistance grounds; after repairs clear codes and perform drive cycle to verify fault does not return
If tests point to ECM driver failure only after wiring and components verified good, follow manufacturer procedures for ECM replacement or repair (disconnect battery and follow anti-static/safety procedures)

Likely causes

Blown fuse or bad relay feeding bank 2 heater
Open/shorted wire or poor connector at catalyst heater bank 2
Failed heater element in the bank 2 catalyst

Fault status

⚠️ Status

Bank 2 catalyst heater supply voltage out of range or circuit fault (open/short/low/high) when heater is commanded — repairs needed to heater supply, ground, element or control.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours