C2124 – Data from transmitter ID 4 not received (main) (Lexus)

Lexus-specific code — factory diagnostic data

C2124 means the Lexus CT200h tire pressure monitoring system cannot “hear” one of the registered transmitters. You will usually see a TPMS warning and no pressure reading for one tire position in the display, even if the tire pressure looks fine. According to Lexus factory diagnostic data, this code indicates “Data from transmitter ID 4 not received (main).” This is a manufacturer-specific chassis code, so the exact logic and naming can vary by Lexus platform. Treat it as a direction to test why the tire pressure monitor stops receiving that transmitter’s radio message, not as proof the sensor failed.

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C2124 Quick Answer

C2124 sets when the Lexus tire pressure monitor does not receive the expected data message from “transmitter ID 4” in the main TPMS set. Diagnose signal reception, sensor registration, and related power/radio issues before replacing any parts.

What Does C2124 Mean?

Official definition: “Data from transmitter ID 4 not received (main).” In plain terms, the TPMS ECU (tire pressure monitor) expects periodic pressure/temperature/ID updates from each learned sensor. When one learned sensor stops reporting, the ECU flags the missing one as ID 4 in the main set. In real use, the system cannot reliably warn you about a pressure loss for that tire position until the fault clears.

What the module actually checks: the tire pressure monitor tracks a learned ID list and monitors message timing and validity for each ID. C2124 triggers when the ECU does not receive the expected RF data for the ID stored in the “ID 4” memory slot of the main set. Why that matters: the DTC points to a suspected trouble area (loss of transmitter data), so you must confirm whether the issue comes from a dead sensor, an unregistered/mismatched ID, low tire pressure preventing wake-up, RF interference, or a receiver/antenna/power problem that affects reception.

Theory of Operation

On Lexus TPMS, each wheel sensor transmits a unique ID with pressure and temperature data by radio frequency. The tire pressure monitor stores several IDs and compares received messages against its learned list. Under normal conditions, it receives periodic updates while driving and confirms each ID remains active.

C2124 appears when the ECU’s main ID list includes a sensor stored as “transmitter ID 4,” but the ECU stops receiving valid messages from that ID within its expected time window. That breakdown can happen because the sensor never wakes up, the wrong ID got registered, the sensor battery cannot support transmission, or the vehicle cannot receive the RF signal consistently.

Symptoms

You will usually notice TPMS warning behavior first, then missing data for one learned transmitter.

• TPMS warning TPMS light on or “Check TPMS” message
• Missing reading One tire pressure value does not display or shows dashes
• Delayed update Pressure readings update slowly or only after extended driving
• Intermittent fault Warning comes and goes with temperature, speed, or weather changes
• Stored DTC C2124 returns immediately after clearing if the sensor remains silent
• Multiple TPMS codes Additional “transmitter not received” codes may appear if reception drops broadly
• Failed relearn ID registration or initialization does not complete successfully

Common Causes

• Transmitter ID 4 not registered to the “main” TPMS set: The tire pressure monitor will flag C2124 when it never receives a valid ID 4 message that matches the stored main ID list.
• Wrong wheel/tire set selected (main vs second): If the CT200h stores multiple TPMS ID sets, the module can “look” for ID 4 in the wrong set and log a not-received fault.
• Low transmitter battery or weak RF output: A marginal sensor battery can reduce transmit strength so the receiver misses messages, especially after temperature changes.
• TPMS transmitter not transmitting (internal fault or damage): Physical damage or an internal sensor failure can stop the unit from sending data, so the ECU never sees ID 4.
• Aftermarket transmitter incompatible or cloned incorrectly: Incorrect protocol, wrong frequency for the Lexus system, or a bad clone can prevent the tire pressure monitor from accepting the message.
• Intermittent RF interference or poor reception environment: Strong RF noise or shielding conditions can block reception long enough for the module to set a “not received” code.
• Tire pressure monitor antenna/receiver issue (if equipped separately): An antenna circuit fault or failed receiver stage can prevent the module from hearing one or more transmitters.
• Power/ground integrity problem at the tire pressure monitor: Voltage drop on B+ or ground can reduce receiver sensitivity and cause missed transmitter data.
• Harness or connector damage at the TPMS ECU/receiver: Corrosion, backed-out pins, or water intrusion can interrupt antenna paths or module operation and lead to missing transmitter data.

Diagnosis Steps

You need a scan tool that supports Lexus TPMS data and utility functions, plus a digital multimeter for voltage-drop checks. A TPMS trigger tool helps confirm each transmitter can wake and transmit. Use basic hand tools for access and connector inspection. If available, use an RF/TPMS tester to validate the sensor’s signal quality without guessing.

1. Confirm C2124 in the tire pressure monitor and record freeze frame data. Focus on ignition state, vehicle speed, battery voltage, and any related TPMS DTCs. Freeze frame shows the conditions when the fault set. Use a scan-tool snapshot during a drive to capture intermittent dropouts that freeze frame cannot show.
2. Run a full network scan and confirm the tire pressure monitor appears and communicates. Then check TPMS-related fuses and power distribution feeds first. Do not backprobe the ECU until you verify the upstream supply path.
3. Verify tire pressure monitor power and ground with voltage-drop testing under load. Turn the circuit on and load it, then measure drop on the B+ feed and the ground path. Keep ground drop under 0.1V with the circuit operating. Do not trust continuity checks alone for high-resistance faults.
4. Use the scan tool to view TPMS live data and confirm which ID set the system currently uses. Check whether the CT200h shows a “main/second” selection or ID list status. If the tool supports it, read the stored transmitter IDs and confirm that “transmitter ID 4” actually contains an ID value.
5. Check whether C2124 is pending or confirmed/stored. A pending code suggests an intermittent receive issue or a recent configuration change. A confirmed/stored code usually means the condition repeated over consecutive drive cycles. If the fault returns immediately after clearing on key-on, treat it like a hard fault in the monitored path.
6. Perform a visual inspection of the TPMS ECU/receiver connector area and related harness routing. Look for water intrusion, green corrosion, bent pins, or a connector that will not fully latch. Pay attention to any recent work that could disturb wiring, such as wheel/tire service or interior trim access near the TPMS unit.
7. Use a TPMS trigger tool to wake each transmitter one at a time and watch the scan tool for reception. Do not assume “ID 4” equals a specific wheel position. Instead, identify which physical wheel produces which received ID on the scan tool, if the data stream supports it. If one transmitter never responds to a trigger, treat that sensor as suspect only after confirming it has the correct type and programming.
8. If the sensor responds to a trigger tool but the vehicle still logs C2124, verify the transmitter ID programming. Re-register the transmitter IDs to the main set using the Lexus-compatible scan tool function. Then confirm the system uses the intended set. Configuration errors create “not received” faults even when the hardware works.
9. If the sensor does not respond, swap its physical location with a known-good wheel/transmitter when practical. Then repeat the trigger test and monitor which ID fails to report. If the failure follows the sensor, you confirmed a transmitter-side problem. If the failure stays with the vehicle reception regardless of location, you need to focus on receiver/antenna and module power/ground.
10. Check for reception pattern problems using live data during a short drive. Use a scan-tool snapshot to capture when ID 4 drops out and whether other IDs also show missed updates. A single missing ID points toward that transmitter or its programming. Multiple missing IDs point toward receiver sensitivity, antenna circuit issues, power/ground drops, or RF interference.
11. After repairs, clear DTCs and recheck live TPMS data until all registered IDs report normally. Complete a drive cycle and verify C2124 does not return as pending or confirmed. Re-scan the vehicle to confirm no related TPMS codes remain.

Professional tip: When C2124 shows up after tire service, suspect an ID registration or “main vs second set” selection issue first. Confirm the active ID list on the scan tool before you touch parts. A perfectly good transmitter will look “dead” to the ECU if the stored main ID does not match what the sensor broadcasts.

Possible Fixes

• Re-register TPMS transmitter IDs to the correct “main” set using a Lexus-capable scan tool, then verify the active set selection.
• Correct an incorrect or incompatible aftermarket sensor by installing the proper TPMS transmitter type and programming it correctly.
• Repair power or ground issues at the tire pressure monitor using voltage-drop results to locate the high-resistance point.
• Clean, repair, or replace damaged TPMS ECU/receiver connectors or harness sections after confirming pin fit and corrosion issues.
• Replace the confirmed non-transmitting TPMS sensor only after trigger testing and ID verification prove it cannot broadcast.
• Address receiver/antenna faults if multiple transmitters show intermittent reception and wiring/power integrity checks pass.

Can I Still Drive With C2124?

You can usually drive your Lexus CT200h with DTC C2124, but you should treat it as a tire-pressure warning system fault. The tire pressure monitor logged “Data from transmitter ID 4 not received (main).” That means the module cannot “hear” one registered sensor ID. The car will still operate normally, but you lose reliable TPMS coverage for at least one tire. Check pressures with a quality gauge before driving, then set them to the door-jamb specification. Avoid long high-speed trips until you confirm all tires hold pressure. If the TPMS warning flashes first and then stays on, diagnose it soon because the system currently cannot verify inflation on all four corners.

How Serious Is This Code?

C2124 ranges from inconvenience to a real safety concern. It stays minor when all tires hold pressure and you verify inflation manually. It becomes serious when a tire leaks or temperature swings drop pressure overnight, because the Lexus TPMS cannot warn you for the missing transmitter. You may also fail a safety inspection that checks TPMS operation. This code does not create a drivability issue by itself. Still, low tire pressure can cause poor braking, heat buildup, and tire failure. Treat C2124 as a “safety system degraded” condition, not as a reason to park the vehicle immediately.

Common Misdiagnoses

Technicians often replace a sensor immediately because “ID 4” sounds like a specific wheel. On Lexus platforms, the stored ID order does not always match a physical corner after rotations or tire swaps. Another common mistake involves skipping registration checks. A sensor that never got programmed to the tire pressure monitor will look “dead” in data. Shops also miss intermittent RF dropouts from corrosion at a sensor stem, a damaged valve core, or a wheel that blocks signal due to aftermarket components. Finally, people clear codes without driving under the right conditions, then call it fixed when the warning stays off briefly.

Most Likely Fix

The most common confirmed repair direction involves correcting transmitter registration, then confirming the tire pressure monitor receives data during a road test. Many Lexus CT200h cases come down to a sensor ID mismatch after tire service, or a sensor with a depleted internal battery that drops off intermittently. Do not commit to a sensor replacement until you verify the module’s live TPMS data shows no reception for that specific ID, and you confirm the sensor responds to an RF trigger tool while the others respond normally.

Repair Costs

Repair cost depends on whether the confirmed root cause is wiring, connector condition, a sensor, a module, or the labor needed to diagnose the fault correctly.

Last updated: April 8, 2026

Definition source: Lexus factory description · Autel MaxiSys Ultra & EV. Diagnostic guidance is based on factory-defined fault logic for this code.