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DTC codes / BMW codes / P1404

P1404 · BMWHeated Catalyst Current Too High During Heating Bank 2

P1404 on BMW vehicles means the engine control module (ECM) has detected that the electrical current drawn by the bank 2 heated catalytic converter is higher than expected during its heating phase. The ECM monitors this current to ensure the catalyst reaches operating temperature quickly, and an excessively high reading points to a short circuit or a failing heating element.

SystemPowertrain
Code typeBMW specific
SeverityMedium
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • Illumination of the check engine light (CEL) on the dashboard.
  • Often no symptoms besides the warning light, especially if the catalyst still reaches temperature passively.
  • A slight delay in catalyst light-off during cold starts, which may cause a brief rich-running smell.
  • In rare cases, a blown fuse for the heated catalyst circuit, leading to a no-start or other electrical faults.
  • Possible rough running or reduced fuel economy if the ECM limits heating to protect the circuit.
  • Intermittent warning light if the high current is caused by a chafed wire that only shorts occasionally.

Common causes, most likely first

  1. Short circuit in the heated catalyst wiring harness, such as a wire chafed against the chassis or a pinched section.
  2. Failed heating element inside the bank 2 catalytic converter, causing an internal short.
  3. Corroded or damaged electrical connector at the heated catalyst, creating excessive resistance or a short.
  4. Faulty heated catalyst control module or relay, if equipped, that fails to regulate current properly.
  5. Water intrusion into the connector or heating element, leading to a short circuit.
  6. Aftermarket or incorrect replacement catalytic converter with a heating element that draws too much current.
  7. ECM internal fault misreporting the current, though this is rare and should be diagnosed last.

How to diagnose and fix it

  1. Scan all modules for fault codes and record freeze-frame data to confirm P1404 is current and not stored from a past event.
  2. Visually inspect the bank 2 heated catalyst wiring harness and connector for chafing, corrosion, or water intrusion.
  3. Measure the resistance of the heating element with a multimeter and compare to BMW specifications; an out-of-range low resistance indicates a short.
  4. Check the fuse and relay for the heated catalyst circuit, replacing any blown fuse only after finding the cause of the excessive current.
  5. Perform a voltage drop test on the ground and power circuits to the heating element while activating the heater with a scan tool.
  6. If the wiring and element test good, substitute a known-good control module or relay to rule out a faulty component.
  7. As a last resort, replace the bank 2 catalytic converter if the heating element is confirmed shorted internally.

Before you replace the catalytic converter

  • A chafed wire in the harness is far more common than a failed catalyst on BMWs, so always trace the circuit before condemning the converter.
  • The heating element only operates during cold starts, so a short may not appear during a warm-engine test; perform diagnostics with the engine cold.
  • Water can collect in the connector cavity and cause a short that mimics a failed element, so check for green corrosion and moisture.
  • Some aftermarket catalytic converters use a heating element with different resistance, triggering P1404 even though the part is new.
  • The ECM may set P1404 if the battery voltage is low during heating, causing the current regulation to go out of range, so check the charging system first.

Can I keep driving with P1404?

You can generally drive the vehicle with P1404 set, but avoid extended idling and cold-start short trips until repaired, as the catalyst may not heat properly and emissions will be higher. If the check engine light flashes or you notice rough running, stop driving and seek service immediately.

Tools that help

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Guidance is general and written for BMW vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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