P0423Powertrain
Powertrain · SAE
Heated Warm-Up Catalyst Efficiency Below Threshold — Bank 1
Meaning
The catalyst monitor detects that the bank 1 electrically heated warm-up catalyst (HCC) does not reach the efficiency threshold during the pre-heating phase. The heating system or the catalytic substrate are compromised.
Common causes
- Faulty catalyst heating element (HCC) or open circuit in the heater circuit
- Depleted or poisoned substrate despite electrical heating
- Blown fuse or failed relay in the heater circuit
- Faulty downstream sensor compromising the monitor reading
- Damaged connector or wiring of the catalyst heater
Symptoms
- Malfunction indicator lamp (MIL) on
- Elevated emissions especially during cold start
- Engine performance normal at operating temperature
- Possible additional DTC related to the HCC heater circuit
- Sometimes no noticeable symptoms
Severity
Moderate: emissions exceed limits during start-up; the problem worsens if the catalytic substrate is also damaged beyond the heater.
What to do
- Check the catalyst heater power supply and circuit (fuse, relay, wiring)
- Measure heating element resistance (compare to nominal value)
- Check the downstream sensor and catalyst OSC values with a scan tool
- Look for additional DTCs related to the HCC heater circuit
- Replace the heated catalyst unit if the heater is intact but efficiency is confirmed insufficient