U04B4: Invalid Data Received From Brake Blending Actuator
A receiving module detected implausible data from the brake blending actuator (manages mix of regen + friction braking on hybrids/EVs). Pressure command vs. actual fails plausibility checks and is rejected.
What U04B4 means
U04B4 is a generic OBD-II network code in the invalid data & software group. In plain English: a module received data that didn’t make sense from the Brake Blending Actuator.
- Check engine light
- Usually on
- Emissions-related
- No
- Limp mode possible
- Yes
- Drive cycle to clear
- Required
Get it fixed
Post this code once and get quotes from local mechanics. Free to post.
Makes the repair and parts links below specific to your car. Kept in this browser only.
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
- 01Module internal fault or sensor input driftMost likely
- 02Software version mismatch after replacementPossible
- 03Gateway module routing CAN messages incorrectlyLess likely
Can I drive with U04B4?
Not recommended beyond getting it to a shop.
This fault can put the engine or transmission in limp mode with reduced power, which can make merging and passing unsafe. Have it diagnosed as soon as possible.
Why we rate it urgent
- Can put the vehicle in limp mode (reduced power)
- Turns on the check engine light
- Needs a drive cycle to confirm a repair
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose U04B4
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just U04B4. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Fix other faults first
If other codes are stored, start with power-supply, sensor-circuit and communication codes. They can cause this code as a side effect.
- 3
Check module power, ground and the data bus
Confirm the module named in the code has battery voltage, ignition feed and a good ground. With the battery disconnected, a healthy CAN bus usually measures about 60 ohms between CAN-High and CAN-Low at the OBD port. Inspect connectors for corrosion and pushed-out pins.
- 4
Test the likely causes in order
Start with the most likely cause and work down: Module internal fault or sensor input drift; software version mismatch after replacement; gateway module routing CAN messages incorrectly. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and complete a full drive cycle (cold start, idle, steady highway cruise, deceleration). The code is fixed when the related readiness monitor completes without it returning.
U04B4 repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Hard
- Good DIY job?
- Usually a shop job
Involved testing or major parts. Most owners use a shop.
Parts and systems involved
- Brake blending actuator
U04B4 FAQ
What does U04B4 mean?
U04B4 means “Invalid Data Received From Brake Blending Actuator”. A receiving module detected implausible data from the brake blending actuator (manages mix of regen + friction braking on hybrids/EVs). Pressure command vs. actual fails plausibility checks and is rejected.
Is U04B4 serious? Can I keep driving?
We rate U04B4 as urgent severity. Not recommended beyond getting it to a shop. This fault can put the engine or transmission in limp mode with reduced power, which can make merging and passing unsafe. Have it diagnosed as soon as possible.
What causes U04B4?
The most common causes, from most to least likely: Module internal fault or sensor input drift; Software version mismatch after replacement; Gateway module routing CAN messages incorrectly. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix U04B4?
Typical labor is about $125–$625 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix U04B4 myself?
DIY difficulty is hard. Most owners leave this to a shop because it needs involved testing or specialist tools. Always confirm the cause before buying parts.
Will U04B4 clear itself?
Once the fault is fixed, the check engine light usually goes off by itself after the system passes its self-test over several drive cycles. Clearing the code with a scan tool resets readiness monitors, so an inspection station may turn you away until a full drive cycle is completed.