U04B6 code meaning
Invalid Data Received From Catalyst Heater Control Module
Network system Generic code U04xx codes Check engine light
What U04B6 means
An electrically heated catalyst brings the converter to working temperature right after a cold start. Vitesco's EMICAT heater runs at 12, 24 or 48 V and can draw up to 300 A, has been ordered for 48-volt mild hybrid diesel vans with production planned from 2022, and in high-voltage hybrids is fed by a dedicated DC/DC converter. The electronics that switch this power report heater state and energy to the engine controller. U04B6 is stored when those messages arrive but fail plausibility; no carmaker has published its use of the code. Section (e)(2) of CARB 1968.2 requires OBD to confirm that a heated catalyst reaches its target temperature in time, so the check cannot run without valid data. U01B5 marks lost contact. Expect a MIL and higher cold-start emissions.
U04B6 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyWorkshop only
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of U04B6
- Check engine light on
- Catalyst monitor readiness not set
- Engine may idle longer at raised speed after cold start
Common causes of U04B6
- PossibleHeater control electronics or DC/DC stage faulty
- PossibleHigh-current connection to the heater loose or overheated, giving implausible feedback
- PossibleBus wiring or connector near the hot exhaust damaged
- Less likelyModule and engine controller software not matching
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Catalyst heater module
What each part of U04B6 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| B6 | The exact fault in that area. |
What to do next
- Note U04B6 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U04B6
What does U04B6 mean?
U04B6 means "Invalid Data Received From Catalyst Heater Control Module". An electrically heated catalyst brings the converter to working temperature right after a cold start. It is a generic code, so it means the same on every make.
Is it safe to drive with U04B6?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U04B6 fail an emissions test?
Yes, it can. U04B6 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U04B6 to fix?
Difficulty: workshop only. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U04B6 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.