Catalyst Heater Control Circuit (Bank 2)
The P0439 code means the vehicle's onboard diagnostic system has detected: Catalyst Heater Control Circuit (Bank 2). This is a low severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $100 - $500 (parts and labor)
Reads enhanced codes and shows real-time O2 sensor data. Verify the cat is actually bad before dropping $1,000+ on a replacement.
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Common Symptoms
- Check Engine Light illuminated
- Higher cold-start emissions on Bank 2
- No noticeable drivability issues
- Failed emissions test
Probable Causes (Ranked by Likelihood)
- Failed Bank 2 catalyst heater relay or fuse Very High
- Open or shorted Bank 2 heater control wiring High
- Failed Bank 2 catalyst heater element Moderate
- ECM Bank 2 heater control driver fault Low
Frequently Asked Questions
Can I drive with code P0439?
Yes. The Bank 2 catalyst heater circuit fault only affects cold-start emissions. Normal driving is unaffected.
Is P0439 the Bank 2 version of P0429?
Yes. P0429 covers Bank 1 catalyst heater control circuit and P0439 covers Bank 2. Diagnostics are the same on the opposite bank.
Can both P0429 and P0439 set together?
Yes. If both banks share a fuse or relay, a single component failure can set codes for both banks. Check shared components first when both codes are present.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Check the catalyst heater fuse and relay for Bank 2
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Measure Bank 2 heater element resistance at the connector
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Verify ECM commands the Bank 2 heater on during cold start
-
Check for voltage at the Bank 2 heater connector during cold start
-
Inspect wiring from ECM to Bank 2 heater element for damage
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
Commonly Affected Vehicles
- 2004-2016 Lexus RX 400h
- 2005-2018 Toyota Highlander Hybrid V6
- 2006-2018 Lexus GS 450h
- 2007-2019 Lexus LS 600h
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