U0104 Code: Lost Communication With Cruise Control Module
The adaptive cruise radar (or cruise module) went silent on the network, so cruise is switched off.
At a glance
Severity: Low
- Meaning
- Lost Communication With Cruise Control Module
- System
- Module Communication · Network
- Safe to drive?
- Yes, short term
- Typical repair cost
- $50–$2,200
- DIY difficulty
- Moderate
On most modern cars the 'cruise control module' in U0104 is the adaptive cruise radar sensor, mounted behind the grille emblem or low in the front bumper cover. It measures distance to the vehicle ahead and sends speed and braking requests to the PCM and ABS module; on many cars it also feeds forward collision warning and automatic emergency braking. When the PCM or ABS module stops receiving its messages, it logs U0104 and disables adaptive cruise, and often the collision-warning features too. The front bumper is a harsh place for electronics, so minor impacts, body-shop work that disturbed the connector and water in the harness are far more common causes than on modules tucked inside the cabin.
Can I keep driving? The car drives and brakes normally; you just lose adaptive cruise and possibly forward collision warning and automatic emergency braking. Drive with full attention to following distance until it's repaired.
How to read U0104
- U Network
- 0 Generic (SAE)
- 1 Module Communication
- 04 Specific fault
Symptoms
- 'Adaptive cruise not available' or 'Cruise control fault' message
- Cruise set button does nothing
- Forward collision warning or automatic emergency braking reported as unavailable
- Warning appears right after a car wash, heavy rain or a bumper repair
- Other modules (ABS, PCM) store U0104 as a history code after a low-battery event
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Radar connector damaged, corroded or left unplugged after bumper or grille work
- Collision damage to the radar sensor or its bracket, even from a minor parking bump
- Water or road salt in the radar connector or the harness behind the bumper
- Blown fuse or poor power/ground feeding the radar module
- Internal radar sensor failure
- Low battery voltage causing the module to drop out at start-up
Diagnosis step by step
Scan the radar module directly
Use a scan tool that can reach driver-assistance modules. If the radar answers, read its own codes for misalignment, blockage or internal faults; if it doesn't answer at all, concentrate on its connector, supply and CAN lines.
Tools: OBD-II scanner
Inspect the sensor and bumper area
Look behind the grille emblem or lower bumper opening for cracks, a broken or bent bracket, and whether the sensor is sitting square. Ask about recent parking bumps, grille replacement or bumper removal.
Tools: Flashlight
Check the radar connector
With the ignition off, reach or remove the bumper cover as needed and unplug the radar. Look for water, green corrosion, a missing seal or a connector lock that was never clicked home after previous work.
Tools: Flashlight, Screwdriver
Measure supply and bus lines
Back-probe the radar connector with the key on: battery voltage on the supply pin, a solid ground, and roughly 2.4 to 2.6 V on each CAN line. Some radars sit on a separate chassis or private CAN, so check the diagram for the gateway it connects through.
Tools: Multimeter
Replace and calibrate if needed
If supply and bus are good and the radar still won't answer, replace it. Any new, removed or re-bracketed radar must be aimed and calibrated to the manufacturer's procedure, either with a static target setup or a guided calibration drive.
Tools: OBD-II scanner
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace fuse or repair radar connector | No | $50–$300 |
| Replace radar mounting bracket and recalibrate | No | $250–$600 |
| Radar aiming/calibration only | No | $150–$450 |
| Replace adaptive cruise radar sensor with calibration | No | $900–$2,200 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Field data
| Honda | 3 | Odyssey, Passport, Pilot |
|---|
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Usually passes
U0104 doesn't normally turn on the check engine light and has no emissions impact, so it passes a US emissions test. Safety inspections generally don't check adaptive cruise.
Frequently asked questions
Is it safe to drive with U0104?
Yes, the brakes, steering and engine are unaffected. Just remember that automatic emergency braking and collision warning may be off too, so leave a bigger gap.
Why did this appear right after a bumper repair?
The radar has to be unplugged, and often unbolted, when the bumper cover comes off. A connector not fully latched, a pinched harness or a missing calibration afterward are the usual reasons the code shows up after body work.
Can snow or dirt on the sensor cause U0104?
A blocked sensor usually gives a 'sensor blocked' message rather than a lost-communication code, and it clears once you clean it. If the message stays after cleaning and the radar doesn't respond to a scan tool, it's an electrical or module problem.
Does a new radar need calibration?
Always. Even a small aiming error can make adaptive cruise brake for cars in the next lane or miss the one ahead. Calibration requires proper equipment and a level floor or a specified test drive.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- NHTSA Complaints API
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy