C000B – ACC communication timeout

C000B means the vehicle lost communication with the Adaptive Cruise Control (ACC) system long enough to time out. In plain terms, cruise control features may disable, and you may see an ACC or driver-assist warning. The car can still run normally, but you lose a safety and convenience function. According to factory diagnostic data, this code indicates an “ACC communication timeout,” which points to a network or module communication problem, not an automatic ACC unit failure. Start by confirming whether the ACC module appears on a full vehicle network scan and whether the fault comes back as pending or confirmed.

C000B Quick Answer

The C000B code points to a timeout in messages to or from the ACC system. Check for ACC module presence on the scan tool first, then verify ACC power/ground and network wiring integrity.

What Does C000B Mean?

C000B meaning: “ACC communication timeout.” A chassis or driver-assist related control module set this code after it stopped receiving expected ACC-related communication. In practice, the vehicle often disables adaptive cruise control and may limit related features like forward collision alerts, depending on the platform.

Technically, the setting module monitors network message traffic and expects periodic ACC status data. When that data does not arrive within the required time window, it logs C000B as a communication loss fault. That matters because a timeout can come from power or ground dropout at the ACC module, a bus wiring or connector problem, network interference from another module, or a scan tool “global” issue. You must prove the network and module basics before suspecting an ACC component.

Theory of Operation

Under normal conditions, the ACC control unit and the chassis/ADAS gateway exchange status, target data, and diagnostic “heartbeat” messages across the vehicle network. The instrument cluster and other controllers rely on those messages to allow ACC engagement and to display driver warnings. The network also carries requests and acknowledgments, so multiple modules must agree before ACC activates.

C000B sets when that message flow breaks. A brief voltage dip, an intermittent connector, water intrusion at a splice, or a noisy network can stop ACC messages long enough to trigger a timeout. Some vehicles route ACC traffic through a gateway, so a gateway reset or bus-off event can mimic an ACC failure. Because the code only reports a communication timeout, diagnosis must confirm whether the ACC module went offline, the bus went down, or another module blocked traffic.

Symptoms

C000B symptoms usually show up as disabled driver-assist features and scan tool communication problems.

• Scan tool: ACC module missing from the module list, “no communication,” or intermittent dropouts during a network scan
• ACC disabled message: adaptive cruise will not set, will cancel, or will not resume
• Warning indicators: ACC/ADAS warning light, “cruise unavailable,” or driver-assist fault message in the cluster
• Feature limitations: forward assist or distance control functions may stop working or operate in a reduced mode
• Intermittent behavior: the fault clears after a key cycle, then returns after bumps, rain, or temperature changes
• Multiple network DTCs: related U- or C-network codes stored in other chassis or gateway modules

Common Causes

• ACC module offline on the network: The ACC controller stops responding to network messages, so other chassis modules log a communication timeout.
• Power feed interruption to the ACC module: A blown fuse, failed relay, or poor power distribution drops module voltage and ends communication.
• High-resistance ACC ground connection: Corrosion or a loose ground eyelet causes voltage drop under load, which makes the module reset or “brown out.”
• Connector fretting or water intrusion at ACC-related connectors: Terminal spread, oxidation, or moisture increases resistance and creates intermittent message loss.
• Network wiring fault (CAN/LIN splice, twisted pair damage, partial open): A compromised data circuit distorts the signal and prevents valid ACC messaging.
• Short-to-power or short-to-ground on the communication lines: A chafed harness or pinched wiring can pull the bus out of its normal bias and block traffic.
• Another module or aftermarket device disrupting the bus: A gateway, telematics unit, audio amp, remote start, or tracker can flood the network or hold it dominant.
• Incorrect coding, software mismatch, or recent module programming event: A configuration error can stop the ACC module from “handshaking” correctly, which looks like a timeout.
• Control module issue (rare): Internal ACC module faults can prevent normal boot-up or message transmission, but you must prove power, ground, and bus integrity first.

Diagnosis Steps

Use a bidirectional scan tool that can run a full network scan and display module status. You also need wiring diagrams, a DVOM, and back-probing tools. For intermittent C000B problems, add a lab scope for CAN/LIN waveform checks. Plan on voltage-drop testing under load and careful connector inspection.

1. Confirm C000B and record freeze-frame data and DTC status. Note ignition state, vehicle speed, battery voltage, and any other communication or chassis DTCs. Separate pending from confirmed/stored codes, since a pending event often points to an intermittent drop-out.
2. Run a complete network scan and check whether the ACC module appears and communicates. If the scan tool shows “no response” for ACC, treat this as an offline module or a bus problem. If ACC communicates, focus on intermittent timeouts and related modules.
3. Check fuses, relays, and power distribution that feed the ACC module and any gateway involved. Verify the correct fuse has power on both sides with ignition ON. Do not start circuit probing at the module until you prove the upstream feeds.
4. Verify ACC power and ground under load using voltage-drop testing. Load the circuit by commanding ACC on (or with key ON and systems awake) and measure drop from battery positive to the ACC B+ pin, then from ACC ground pin to battery negative. Keep ground drop under 0.1V with the circuit operating, because high resistance can reset the module.
5. Inspect ACC-related connectors and harness routing next. Focus on areas that see water, road spray, or front-end impact repairs. Look for backed-out pins, terminal spread, green corrosion, and harness chafe near brackets and splices.
6. Check network integrity at the ACC connector and at accessible splice packs. With ignition ON, verify the communication line bias voltage is present, since ignition-OFF readings do not provide a valid reference. If you find the bus pulled high or low, isolate by unplugging modules one at a time per the wiring diagram.
7. If the ACC module does not appear on the network scan, unplug the ACC connector and recheck network behavior. A shorted module or connector can drag the bus down and hide other controllers. If the bus returns to normal with ACC unplugged, you now have a strong direction for further pin-level testing.
8. Perform pin-to-pin continuity and short checks only after the visual and power/ground tests. Check for opens between ACC and the splice/junction, and check for shorts to power or ground. Wiggle the harness while monitoring resistance to catch intermittent breaks.
9. Use a scan tool snapshot during a road test if the code is intermittent. Freeze frame shows conditions when the DTC set, while a snapshot captures the live moment communication drops out. Log vehicle speed, ignition state, system voltage, and module online/offline status during the event.
10. After repairs, clear codes and rerun a network scan. Confirm ACC stays present, the warning messages do not return, and C000B does not reset during the same ignition-state conditions shown in freeze frame. Recheck for pending codes after a drive cycle to verify the fix.

Professional tip: Do not trust a “good” ground found with an ohmmeter. Always voltage-drop test the ACC ground with the circuit awake and loaded. Many C000B comebacks trace to a ground that reads fine unloaded but drops voltage when the module boots and starts transmitting.

Possible Fixes

• Repair power feed issues to the ACC module, such as a blown fuse, poor fuse contact, or relay/power distribution fault.
• Clean, tighten, and retest ACC grounds, then verify less than 0.1V drop under load.
• Repair damaged network wiring, including twisted pair sections, splice packs, and chafed areas that cause shorts or opens.
• Remove corrosion, correct terminal fit, and reseat ACC and gateway connectors; apply appropriate terminal service procedures as needed.
• Identify and correct an aftermarket device or another module that disrupts network traffic or bus bias.
• Update configuration or software only after you confirm stable power, ground, and network integrity.
• Replace the ACC control module only after testing proves it fails to boot or communicate with known-good power, ground, and bus circuits.

Can I Still Drive With C000B?

You can usually drive with a C000B code, but treat it as an ADAS safety issue. C000B means the vehicle timed out waiting for Adaptive Cruise Control (ACC) communication, so ACC may disable without warning. That can remove automatic following distance control and may also limit related features on some platforms. Drive normally, keep larger gaps, and avoid relying on ACC or driver-assist functions until you fix the fault. If the cluster shows multiple warnings, steering/brake assist changes, or the vehicle enters a reduced-function mode, stop and diagnose immediately.

How Serious Is This Code?

C000B ranges from an inconvenience to a real safety concern, depending on what drops offline. If only ACC quits, the vehicle often drives fine with manual throttle and braking. The risk rises when the communication loss affects shared chassis networks, since other modules may also miss messages. That can disable AEB, forward collision warnings, or stability-related features on some vehicles. After any ACC module, radar, camera, or related control unit replacement, calibration or initialization may be required before the system is safe to use. Plan to confirm calibration status with the correct scan tool and service information.

Common Misdiagnoses

Technicians often replace the radar sensor, camera, or ACC module too early. A timeout code points to a missing message, not a bad sensor. Another common miss involves power and ground testing with no load. The module may “test good” with a meter, yet fail under vibration or current draw. Shops also overlook network basics, like a backed-out terminal at the ACC connector, water intrusion at a front bumper harness joint, or a poor splice in a CAN branch. Avoid wasted spending by proving module presence on a network scan, then verifying power, ground voltage drop, and CAN circuit integrity before replacing anything.

Most Likely Fix

The most frequent confirmed repair path for C000B starts with restoring reliable ACC module power and ground, then fixing the network connection. . A second common fix involves repairing harness damage from minor impacts or aftermarket bumper work. Only after the module stays online, passes a network scan, and the code remains cleared should you consider module replacement. If replacement occurs, complete required ADAS calibration and then road-test to verify the timeout does not return.

Repair Costs

Network and communication fault repairs vary by root cause — wiring/connectors are often the source, but module-level repairs or replacements can be significantly more expensive.

Last updated: March 29, 2026