C1642 – CAN Message failure – Brake (Hyundai)

Hyundai-specific code — factory diagnostic data

C1642 means the front camera system has stopped receiving brake information over the vehicle network. On a Hyundai IONIQ 5, that often shows up as disabled driver-assist features and warning messages, even though the brakes may still feel normal. According to Hyundai factory diagnostic data, this code indicates a “CAN Message failure – Brake.” The source module that sets it is F-CMR (Front View Camera). Treat this as a network-message problem first. Do not assume a failed camera or brake module until you confirm CAN communication and brake-message availability.

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C1642 Quick Answer

C1642 sets when the F-CMR (Front View Camera) cannot see the expected brake-related CAN message. Fix it by verifying network integrity and the brake message source module communication before replacing parts.

What Does C1642 Mean?

Official definition: “CAN Message failure – Brake.” In plain terms, the front camera module expected brake status data and did not get it. In real driving, the camera loses a key input used to control ADAS behavior. That can disable or limit functions that depend on knowing when you brake.

What the module checks and why it matters: The F-CMR monitors specific brake-related CAN frames for presence and plausibility. It also watches timing, counters, and message freshness. When the message drops out or turns invalid, the camera cannot trust braking intent or deceleration. Diagnosis must focus on message loss causes. Those include CAN wiring faults, power/ground issues at a network node, a gateway routing issue, or the brake-message source module going offline.

Theory of Operation

Under normal operation, multiple Hyundai chassis and driver-assist modules share data over. The brake system broadcasts brake pedal status, brake switch state, and other brake-related signals. The F-CMR uses that data to adjust camera-based control logic. It also uses it to reduce false interventions during braking.

C1642 sets when that brake CAN data fails integrity checks. The most common failure mode is “no signal” to the F-CMR from the brake message stream. A second pattern involves intermittent dropouts that exceed the camera’s timeout window. Wiring resistance, connector fretting, or a module reset can cause those dropouts. A gateway or routing fault can also block brake messages from reaching the camera even when the brake module still broadcasts them.

Symptoms

Because this is a CAN message failure seen by the front camera, symptoms often show up as ADAS feature limits plus network-related scan results.

• Scan tool behavior Intermittent module communication, stored U/C-chassis codes, or missing data PIDs for brake status in the camera module
• ADAS warnings Forward safety, lane features, or smart cruise limitations with related messages
• Braking input data Brake pedal/brake switch status not updating in F-CMR live data
• System disable Camera-based functions disable after startup or during a drive
• Intermittent faults Features work briefly, then drop out after bumps or temperature changes
• Multiple DTCs Additional network or power supply codes in chassis or ADAS modules
• No drivability change Normal brake feel, since the fault targets message sharing, not hydraulic operation

Common Causes

• CAN bus open on CAN-H or CAN-L near the camera harness: An open increases bus resistance and breaks the brake message path the F-CMR needs.
• CAN bus short between CAN-H and CAN-L: A short collapses differential signaling and prevents clean message decoding.
• CAN bus short to ground or short to battery: A power or ground short forces the line out of its normal bias range and corrupts messages.
• High-resistance splice or connector fretting at an in-line junction: Added resistance distorts waveform edges and causes intermittent “no signal” behavior under vibration.
• Poor F-CMR power or ground (voltage drop under load): The camera module can reset or brown out and stop receiving brake CAN messages.
• Brake-related sender module offline on the network: If the module that broadcasts brake status drops off the CAN network, the F-CMR logs a brake message failure.
• Incorrect configuration or variant coding after repair (FTB -2E Not Configured when present): Mismatched coding can make the F-CMR reject the expected brake message format or ID.
• Aftermarket device or scan tool pass-through causing bus loading: Extra load can degrade CAN signal quality and trigger message failures during key-on or driving.

Diagnosis Steps

You need a scan tool that can run a Hyundai network scan and view module status. Use a quality DVOM for voltage-drop checks. A scope helps for CAN waveform verification, but you can still find most faults without one. Gather basic back-probe pins and terminal inspection tools. Plan access to the F-CMR connector and a convenient CAN splice or gateway connector.

1. Confirm C1642 in the F-CMR (Front View Camera) and record freeze frame data. Focus on ignition state, vehicle speed, battery voltage, and any companion CAN or brake-related DTCs. Freeze frame shows conditions when the code set. Use a scan tool snapshot later to catch intermittent dropouts during a road test.
2. Run a full network scan and verify the F-CMR appears online. Check whether any brake-related modules show “no communication.” If the scan tool cannot see the F-CMR, treat this as a power/ground or CAN backbone fault first. Communication-related DTCs often show as pending first, then confirmed after two trips. A hard CAN short usually returns immediately at key-on.
3. Check fuses and power distribution that feed the F-CMR and CAN-related junctions. Use a test light or DVOM on both sides of each fuse with the circuit powered. Do not jump straight to the module connector. A partially melted fuse leg can pass continuity but fail under load.
4. Verify F-CMR power and ground with voltage-drop testing under load. Turn the system on so the camera operates. Measure voltage drop on the B+ feed path and on the ground path while the module stays connected. Keep ground drop under 0.1V with the circuit operating. If you find excessive drop, repair the feed, ground point, or connection before any network testing.
5. Inspect the F-CMR connector and nearby harness routing. Look for water entry, bent pins, terminal spread, or corrosion. Pay attention to areas that flex, such as near the windshield header or A-pillar transitions. Fix terminal tension issues instead of forcing the connector back together.
6. Inspect CAN wiring integrity on the camera branch. Check for twisted pair damage, chafing, or repairs that untwist the pair. Confirm correct pin fit and that neither CAN wire shows signs of being pulled from the terminal crimp. Poor twist integrity increases noise sensitivity and can trigger brake message failures on Hyundai platforms.
7. Check CAN bus resistance with ignition OFF and the 12V battery disconnected. Measure between CAN-H and CAN-L at an accessible connector, such as the F-CMR connector or a nearby junction. A healthy network typically reads about 60 ohms. Readings near 120 ohms or OL point to an open or missing termination. Very low resistance suggests a short between lines or an added device loading the bus.
8. With ignition ON, check CAN bias voltages to ground at the same access point. Measure CAN-H to ground and CAN-L to ground with the connector back in place when possible. CAN bias only appears with the network powered, so ignition-off readings do not help. Healthy systems often sit near 2.5V on both lines at rest. Large deviations support a short to power, short to ground, or a module pulling the bus down.
9. Use the scan tool to monitor brake-related data the F-CMR relies on, if available. Watch for “brake switch,” “brake applied,” or similar status fields. Compare them to the same parameters in a brake or chassis control module data list. If the brake module shows stable data but the F-CMR shows invalid or missing data, you likely have a network branch issue or F-CMR power integrity problem.
10. If the fault appears intermittent, perform a controlled wiggle test while logging a scan tool snapshot. Move harness sections near the camera, A-pillar, and junction connectors. Look for the exact moment communication drops. Correlate the drop with voltage-drop changes or CAN bias shifts. This isolates a high-resistance connector or broken conductor without guessing parts.
11. Clear codes and run a key cycle and road test under similar conditions to the freeze frame. Recheck for pending versus confirmed C1642 and any companion CAN DTCs. Confirm the F-CMR keeps brake message status stable during the drive. Only after stable communication returns should you consider module programming or replacement steps.

Professional tip: Treat C1642 as a “suspected trouble area” code, not a failed-part verdict. The F-CMR reports a brake CAN message failure, but the root cause often sits in power/ground integrity or a CAN branch splice. Always prove bus health with resistance (battery disconnected) and bias checks (ignition on). Voltage-drop testing under load catches the faults that continuity checks miss.

Possible Fixes

• Repair CAN-H/CAN-L open, short, or high-resistance section: Restore twisted-pair integrity and correct any improper splices or damaged insulation.
• Clean, repair, or replace affected terminals/connectors: Correct corrosion, water intrusion, pin fit, or terminal spread at the F-CMR or nearby junctions.
• Restore proper F-CMR power and ground: Repair fuse contact issues, feed wiring, or ground points confirmed by voltage-drop testing.
• Remove or correct aftermarket accessories loading the CAN network: Eliminate add-on devices that disturb bus resistance or bias voltage.
• Perform required Hyundai configuration/coding update when verified: If FTB -2E applies, correct variant coding after confirming wiring and network integrity.
• Replace the proven-faulty module only after verification: Replace the F-CMR or the brake-message sender module only if it fails network participation or output tests after wiring checks.

Can I Still Drive With C1642?

You can usually drive with C1642, but you must treat it as an ADAS and brake-data communication concern on the Hyundai IONIQ 5. The F-CMR (Front View Camera) logs this code when it cannot trust brake-related CAN messages. That can disable or degrade camera-based functions that rely on brake status, such as forward safety features, speed assist logic, and warnings. Basic braking typically still works because the foundation brake system does not depend on the camera. Do not assume driver-assist will intervene. Drive defensively, increase following distance, and avoid relying on AEB or cruise-related automation until you confirm the fix.

How Serious Is This Code?

C1642 ranges from an inconvenience to a real safety limitation. It feels minor when only a camera warning appears and driver-assist features shut off. It becomes more serious when multiple network codes appear, when brake lamps act strange, or when several chassis modules lose data at once. Since this is an ADAS-related module, any repair that involves the front camera, its power supply, its network wiring, or related module replacement may require calibration or initialization before the system is safe to use. On Hyundai platforms, calibration commonly needs an OEM-level scan tool and a controlled setup. Verify function after repairs with a road test and scan-tool data.

Common Misdiagnoses

Technicians often replace the front camera because the code sits in the F-CMR. That wastes money when the real fault sits on the CAN network or in a shared power or ground. Another common miss involves blaming the brake actuator or ABS module without confirming message loss on the bus. Some shops clear codes and stop when the light stays off . Intermittent CAN faults return under vibration or load. Avoid these traps by checking for companion codes in ABS/ESC and gateway modules, validating camera power and ground with a loaded voltage-drop test, and confirming CAN integrity at the camera connector before any parts ordering.

Most Likely Fix

The most common confirmed repair directions involve restoring clean CAN communication and stable module power for the F-CMR on the Hyundai IONIQ 5. Start with connector and harness corrections, not parts. Technicians frequently find a loose camera connector, water intrusion at a front harness junction, or damaged twisted-pair wiring that carries CAN signals. A second common fix addresses poor power or ground that makes the camera reset and miss brake messages. Only after you prove good power, ground, and CAN waveforms should you consider camera replacement. If you replace the camera, plan for OEM calibration and a verification drive under the system’s enable conditions.

Repair Costs

Repair cost depends on whether the root cause is a wheel speed sensor, wiring, connector condition, or the hydraulic control unit. Start with electrical checks before replacing brake system components.

Last updated: April 10, 2026