C1E2D00 – RCTB signal communication timeout

C1E2D00 is a manufacturer-controlled chassis diagnostic trouble code (DTC) found in BYD electric and plug-in hybrid vehicles. The C1 prefix places it in the chassis system category under manufacturer-specific coding — meaning it is not a generic OBD2 code and is not shared across other vehicle makes. The code title, RCTB Signal Communication Timeout, describes a condition in which a control module within the vehicle’s CAN bus network has stopped receiving the expected RCTB signal within its required time window. RCTB is a BYD-proprietary signal or module identifier defined within BYD’s own diagnostic and network architecture documentation. As with all CAN communication timeout faults, C1E2D00 may point to the signal source, the network path, or the receiving module — and distinguishing between these requires structured diagnosis, not parts-swapping.

What Does C1E2D00 Mean?

The official title of C1E2D00 is RCTB Signal Communication Timeout. In the context of BYD’s vehicle network architecture, a communication timeout fault is set when a module that depends on a specific CAN signal — here, the RCTB signal — fails to receive that signal within its defined cyclical time window. CAN-based signals are transmitted at regular intervals by a source module and consumed by one or more receiver modules. When the receiving module counts too many missed transmission cycles without a valid message, it logs a timeout fault and stores the code.RCTB is a BYD-specific designation. Without access to BYD’s internal service documentation, its precise expansion cannot be confirmed; however, given BYD’s vehicle architecture — which integrates chassis control functions, regenerative braking management, and traction battery interaction across a shared CAN network — the RCTB signal is likely associated with the interface between chassis-level safety or motion control and the vehicle’s powertrain or energy management layer. The “00” suffix in BYD’s coding convention typically denotes a primary or general instance of the fault rather than a numbered sub-variant.Critically, a communication timeout code does not directly confirm that the named signal source has failed. It confirms only that the expected signal was not received. The fault could originate at the transmitting module, in the wiring or connectors between modules, in the CAN bus itself — such as a short, open circuit, or failed termination resistance — or, less commonly, in the receiving module’s own network interface hardware.

Symptoms

Because C1E2D00 relates to inter-module communication within BYD’s chassis or drivetrain CAN network, symptoms may vary depending on which vehicle functions depend on the RCTB signal and how the affected receiving module responds to the loss of that input. Plausible symptoms include:

• Warning lamp illuminated on the BYD instrument cluster — typically the EV system alert, chassis warning, or a combination of multiple simultaneous alerts
• Reduced or absent regenerative braking, if the RCTB signal contributes to regen control logic
• Vehicle entering a reduced-power or restricted-performance mode, depending on how the receiving module responds to missing input
• Brake system or stability control warnings, if chassis safety functions depend on the affected signal
• Stored or active companion codes in related control modules — particularly other C1-chassis or U-class communication faults
• Hesitation or unexpected behaviour during deceleration, if energy recovery or braking blending is partially disrupted
• No immediately perceptible driveability change in some cases — the fault may present only as a warning lamp, particularly when intermittent

If multiple system warnings are active alongside C1E2D00, map all stored codes together before drawing conclusions about individual components. A cluster of timeout codes across several modules almost always indicates a shared network or supply fault rather than multiple simultaneous module failures.

Common Causes

• CAN bus wiring fault — open circuit, short to ground, or short to power on the CAN High or CAN Low lines serving the affected network segment
• Connector corrosion or damage — water ingress, terminal backing-out, or deteriorated crimp quality at connectors within the affected module circuit
• Source module power or ground fault — the module responsible for generating the RCTB signal has lost its supply voltage or chassis ground, preventing it from transmitting on the network
• CAN bus termination resistance fault — a failed, missing, or incorrectly valued 120-ohm termination resistor causing signal integrity degradation across the bus
• Source module internal failure — the module generating the RCTB signal has failed internally and is no longer transmitting, despite receiving correct power and ground
• Software or calibration mismatch — a module has been replaced or updated with mismatched firmware, producing incompatible or incorrectly timed network messaging
• Intermittent wiring fault — a stress-related harness break or loose connector that only drops the signal under vibration, temperature extremes, or high electrical load conditions
• 12V auxiliary battery degradation — significant voltage drop under load on the auxiliary battery can cause module brownouts and cascading CAN communication faults across BYD’s electronic architecture

Common Misdiagnoses

• Replacing the receiving module first — C1E2D00 is stored by the receiving module, but the fault almost never originates there. That module is reporting the absence of input; it is rarely the cause of the timeout.
• Treating RCTB as a direct part name — RCTB is a signal or module identifier in BYD’s proprietary network, not necessarily a single purchasable component. Misidentifying the signal name as a specific part leads to incorrect parts ordering and wasted expenditure.
• Clearing the code without network testing — if the code returns quickly after clearing, the fault is active. If it does not return, it was intermittent. Neither outcome on its own confirms the root cause without further testing.
• Overlooking CAN bus termination resistance — a failed termination resistor can generate widespread timeout codes across multiple modules simultaneously and is frequently missed during visual inspection alone.
• Ignoring 12V auxiliary battery condition — a weak or failing auxiliary battery in a BYD EV or PHEV can cause cascading network communication faults that closely mimic module-level hardware failures, and it is one of the most commonly overlooked root causes.
• Chasing companion U-codes independently — if other communication faults appear alongside C1E2D00, they must be mapped together as a set to identify the common failure point, not investigated separately as unrelated events.

Common Applications

Make	Model Family	Drivetrain	Notes
BYD	Han EV / Han DM	BEV / PHEV	BYD manufacturer-controlled code; confirmed BYD-only
BYD	Tang EV / Tang DM	BEV / PHEV	Multi-module CAN architecture; RCTB signal BYD-proprietary
BYD	Seal / Seal U DM-i	BEV / PHEV	Exact model year coverage not confirmed from available data
BYD	Atto 3 (Yuan Plus)	BEV	BYD e-Platform 3.0 architecture
BYD	Dolphin	BEV	BYD-specific CAN network architecture
BYD	Song Plus / Song Pro DM-i	BEV / PHEV	PHEV network complexity increases likelihood of inter-module timeout faults

Exact model year and market variant coverage for C1E2D00 is not confirmed from publicly available data. The code is BYD manufacturer-controlled and applies broadly across BYD’s EV and PHEV platform portfolio. Verify applicability using a BYD-compatible enhanced diagnostic tool before drawing conclusions about specific coverage.

Tools & Equipment

Tool	Purpose	Notes
Enhanced scan tool (BYD-compatible)	Read, freeze-frame, and clear C1E2D00; monitor live CAN data	Autel MaxiSYS, Launch X431, or equivalent with confirmed BYD protocol support
Digital multimeter (DMM)	Check module supply voltage, ground continuity, CAN line resistance	Essential for all basic circuit verification steps
Oscilloscope or CAN analyser	Verify CAN signal waveform integrity and identify missing transmitters	Recommended when wiring and supply checks pass but fault persists
BYD-specific wiring diagram	Identify CAN network topology, connector locations, and module pin assignments	Required — do not attempt network diagnosis without correct model-specific diagrams
Battery conductance tester	Assess 12V auxiliary battery health under load	Weak auxiliary battery is a leading and frequently overlooked cause of CAN timeout faults in BYD vehicles
Insulation resistance tester	Check for HV isolation faults if HV-adjacent circuits are suspected	For use by qualified HV-trained technicians only

Step-by-Step Diagnosis

• 1
  Connect a BYD-compatible enhanced scan tool and retrieve all stored codesRecord C1E2D00 along with every companion DTC present — especially other C1-chassis codes and any U-class communication faults from additional modules. Do not clear codes yet. Document freeze-frame data if the tool captures it. A cluster of timeout codes across multiple modules strongly suggests a shared CAN network fault or a common supply issue rather than independent module failures.
• 2
  Test the 12V auxiliary battery conditionMeasure auxiliary battery voltage at rest and perform a load or conductance test. BYD EVs and PHEVs power all control modules — including those responsible for CAN network communication — via the 12V auxiliary system. A battery that drops significantly under load can cause one or more modules to drop off the network intermittently, producing timeout codes including C1E2D00. Address any confirmed battery deficiency before proceeding further.
• 3
  Inspect CAN bus wiring and connectors in the affected network segmentUsing the BYD wiring diagram, identify the network segment carrying the RCTB signal. Visually inspect all accessible connectors in that segment for corrosion, water ingress, bent or backed-out terminals, and damaged insulation. Pay close attention to harness sections that pass through bulkhead grommets, underfloor routing, or areas exposed to thermal cycling and moisture.
• 4
  Measure CAN bus termination resistanceWith the ignition off and both network termination resistors in circuit, measure resistance across the CAN High and CAN Low lines at an accessible connector on the affected bus segment. The combined resistance of two parallel 120-ohm terminators should read approximately 60 ohms. A reading significantly above or below this indicates a broken, missing, or shorted terminator, or a wiring fault that is disrupting the entire network segment.
• 5
  Verify power and ground supply to the source moduleUsing the wiring diagram, identify the module responsible for generating the RCTB signal. Measure its supply voltage against specification and confirm that all chassis ground connections at that module are clean, corrosion-free, and securely torqued. A module that has lost power or a reliable ground will cease transmitting and will cause every dependent receiver to log a timeout fault.
• 6
  Use an oscilloscope or CAN analyser to verify active network communicationIf wiring, connector, supply, and termination checks all pass, connect an oscilloscope or CAN bus analyser to the relevant network segment and observe whether the RCTB signal is being transmitted. A missing or corrupted waveform on an otherwise-powered network with intact wiring points to an internal failure in the source module. A distorted waveform affecting multiple signals simultaneously points back to a wiring or termination issue on the shared bus.
• 7
  Clear codes and retest under operating conditionsAfter any repair action, clear all stored DTCs and exercise the vehicle through a complete drive cycle that activates the affected system. Monitor live CAN data via the scan tool for RCTB signal activity during operation. Confirm C1E2D00 does not return before releasing the vehicle.

Scanner Readout Explained

--- BYD Enhanced Scan Tool — Illustrative Example Only ---

DTC:         C1E2D00
Status:      Stored / Active
Description: RCTB Signal Communication Timeout

Companion DTCs (illustrative — actual codes vary by model):
  U0100       Lost Communication With ECM/PCM (if applicable)
  C1E2C00     Adjacent chassis communication fault (model-dependent)
  U0140       Lost Communication With Body Control Module (if applicable)

Freeze Frame Data (illustrative):
  Vehicle Speed:        0 km/h  (fault often sets at ignition-on or standstill)
  Ignition Voltage:     11.6 V  ← below typical threshold; check 12V aux battery
  Fault Counter:        Multiple occurrences logged
  Fault Type:           Intermittent / Active (verify with live data)

Live Data (illustrative):
  RCTB Signal Status:   Timeout / Not Received
  CAN Bus Status:       Error Detected / Communication Degraded
  Source Module Power:  Verify per wiring diagram

NOTE: All values shown above are illustrative examples only.
Actual freeze-frame data, live values, and companion code sets
will vary by BYD model, software version, market variant, and the
conditions present at the time the fault was stored.
A BYD-compatible enhanced scan tool is required to retrieve this
code with its full description and associated data.

Step-by-Step Repair Guide

The correct repair action for C1E2D00 depends entirely on which root cause is confirmed during structured diagnosis. Do not proceed with any repair path until the fault has been isolated. Three primary repair paths address the most common confirmed causes.

Repair Path A — 12V Auxiliary Battery Replacement

• 1
  Confirm auxiliary battery failureA conductance test result below the manufacturer’s minimum threshold, combined with measurable voltage drop under load, confirms a degraded 12V battery. Note that a battery can appear to start the vehicle normally while still dropping low enough under sustained module load to destabilise CAN network communication in BYD’s architecture.
• 2
  Replace with a BYD-specified auxiliary batteryUse the correct specification battery for the model and variant. Ensure all terminal connections are clean and tightened to the correct torque. Some BYD platforms require the replacement battery to be registered or initialised via a scan tool — verify this requirement for the specific vehicle before releasing it to the customer.
• 3
  Clear all stored codes and retest over a full drive cycleIf C1E2D00 was caused solely by the auxiliary battery, it should not return following a correctly executed replacement and initialisation. Monitor live data during the drive cycle to confirm the RCTB signal is present and stable.

Repair Path B — CAN Bus Wiring or Connector Repair

• 1
  Isolate the specific wiring or connector faultWith the affected network segment identified from the wiring diagram, use a digital multimeter to test for open circuits, shorts to ground, and shorts between the CAN High and CAN Low conductors. Pay particular attention to connectors at module interfaces and harness sections that flex, pass through grommets, or are exposed to moisture and heat cycling.
• 2
  Repair or replace the damaged wiring or connectorsRepair open circuits using correctly rated automotive wire and proper splice methods. Replace corroded or damaged connectors using OEM-specification terminals and housings where possible. Do not use generic butt splices on CAN bus conductors — the twisted-pair characteristic of CAN wiring is important to signal integrity and must be maintained throughout any repair.
• 3
  Verify termination resistance post-repair and retestAfter completing the repair, re-measure CAN termination resistance on the affected segment and confirm the reading is approximately 60 ohms. Clear all stored DTCs, perform a full drive cycle, and confirm C1E2D00 does not return.

Repair Path C — Source Module Software Update or Replacement

• 1
  Check for applicable BYD technical service bulletins and software updates firstBefore ordering hardware, consult BYD’s TSB database or a BYD dealer for any software or firmware updates applicable to the source module. BYD periodically issues updates that address known network communication issues without requiring hardware replacement. This step can avoid unnecessary parts expenditure.
• 2
  Confirm by oscilloscope that the source module is not transmittingOnly proceed to hardware replacement after confirming via oscilloscope or CAN analyser that the RCTB signal is absent on the network despite the source module receiving correct supply voltage and chassis ground. A correctly powered module with no CAN output and no applicable software fix points to an internal hardware failure.
• 3
  Replace and programme the source moduleSource an OEM-specification replacement module. Module replacement on BYD EVs and PHEVs typically requires programming, VIN coding, variant configuration, or system initialisation via a factory-level or enhanced diagnostic tool. Verify the specific programming requirements for the module and model before installation. An incorrectly coded or unconfigured module can introduce new faults or prevent the vehicle from operating correctly.
• 4
  Clear all codes and complete a comprehensive system retestAfter programming is confirmed complete, clear all stored DTCs and perform a full drive cycle. Verify via live data that the RCTB signal is present and stable throughout operation and that no further communication faults appear across any module in the network.

Repair Cost Estimates

Repair	Parts Cost (est.)	Labour (est.)	Total (est.)	DIY Difficulty
12V auxiliary battery replacement	€80 – €180	€40 – €80	€120 – €260	Moderate — registration step may require scan tool
CAN bus wiring or connector repair	€20 – €100	€80 – €220	€100 – €320	Advanced — wiring diagram and DMM essential
CAN termination resistor replacement	€10 – €50	€40 – €100	€50 – €150	Advanced — must locate per wiring diagram
Software / firmware update	€0 – €50	€60 – €160	€60 – €210	Workshop only — BYD-compatible tool required
Source module replacement + programming	€200 – €900+	€150 – €400	€350 – €1,300+	Workshop only — programming and configuration required

All figures are broad indicative ranges only. Actual costs vary by BYD model, market region, parts availability, and workshop labour rates. Module pricing in particular varies significantly depending on the specific module confirmed as faulty. Obtain a confirmed root-cause diagnosis before authorising any parts expenditure.

Prevention & Maintenance Tips

• Test the 12V auxiliary battery at every scheduled service interval — BYD EVs and PHEVs depend on a healthy auxiliary battery for stable CAN network operation, and a degrading battery is one of the most common triggers for communication timeout faults
• Keep all module connectors, ground points, and harness routing brackets clean and securely fastened — particular attention should be given to underbody, door, boot, and bulkhead areas where moisture ingress and thermal stress are most common
• Check for BYD technical service bulletins and available software updates at each service visit — many network communication faults across BYD’s EV and PHEV platforms have been resolved by firmware updates without hardware replacement
• Avoid aftermarket modifications to the 12V electrical system that introduce additional load, resistance, or interference on shared CAN bus circuits
• If the vehicle has been exposed to flooding, prolonged water submersion, or repeated pressure-washing near module connectors, request a comprehensive connector and harness inspection — water ingress is a frequent and often delayed cause of CAN signal degradation
• After any repair involving module replacement on a BYD vehicle, always confirm that the new unit has been correctly programmed and VIN-coded before returning the vehicle to service — an unconfigured module can introduce new communication faults immediately

Frequently Asked Questions

Can I drive my BYD with C1E2D00 active?

It depends on how the vehicle’s systems are responding. If the vehicle has entered a restricted-performance mode, regenerative braking is noticeably absent, or multiple warning lamps are active simultaneously, driving should be kept to a minimum and the fault diagnosed as soon as possible. If the code is stored with no obvious driveability change, limited use may be feasible, but the fault should not be ignored — a communication timeout in BYD’s chassis or drivetrain network can affect safety-critical functions depending on which module and signal are involved.

Is C1E2D00 a generic OBD2 code?

No. C1E2D00 is a manufacturer-controlled code in the C1xxx range, making it BYD-specific. It will not appear on vehicles from other manufacturers. A basic generic OBD2 scan tool may not read it at all, or may display it without the correct description or supporting data. A BYD-compatible enhanced diagnostic tool — such as Autel MaxiSYS or Launch X431 with confirmed BYD coverage — is required to retrieve the full code description, freeze-frame data, and live network status.

Does C1E2D00 mean the RCTB module has failed?

Not necessarily. A communication timeout code is stored by the receiving module — it means that module stopped receiving the RCTB signal, not that the signal source has definitively failed. The actual fault could be in the transmitting module, in the wiring, in a connector, in a CAN termination resistor, or in the 12V auxiliary battery supply. Replacing a module before ruling out these other causes is a common and costly misdiagnosis. Systematic diagnosis is essential before any module replacement is considered.

Can a weak 12V battery cause C1E2D00?

Yes, and this is one of the most frequently missed causes on BYD EVs and PHEVs. All control modules — including those responsible for CAN bus communication — rely on the 12V auxiliary system for their operating power. A battery that drops voltage under sustained load, even one that appears to start the vehicle normally, can cause modules to drop off the network intermittently and trigger timeout codes including C1E2D00. Always test the 12V auxiliary battery early in the diagnostic process before pursuing more complex fault paths.

Will clearing C1E2D00 fix the problem?

No. Clearing the code without identifying and addressing the underlying fault will not fix anything. If the root cause remains, the code will return — sometimes immediately, sometimes after a short drive. Code clearing is a diagnostic step used to distinguish active faults from intermittent stored history codes; it is not a repair action in itself.

Do I need a BYD dealer to diagnose or fix C1E2D00?

For initial diagnostic steps — 12V battery testing, visual connector inspection, and CAN termination resistance measurement — a competent independent workshop equipped with a BYD-compatible scan tool and the correct wiring diagrams can handle the work. If the diagnosis leads to a module software update or hardware replacement requiring VIN coding or system initialisation, access to BYD’s programming environment may be necessary. Support for BYD programming is increasingly available on platforms such as Autel MaxiSYS, but compatibility should be confirmed for the specific module and model year before committing to independent repair.

Are there BYD technical service bulletins for CAN communication faults?

BYD, like other modern EV manufacturers, does issue technical service bulletins (TSBs) and over-the-air or dealer-applied software updates for known network communication issues. The availability of applicable TSBs for C1E2D00 specifically will depend on the model, software version, and market. Checking with a BYD dealer or through a BYD-compatible professional diagnostic platform for any published bulletins before ordering hardware is always recommended — it can save significant time and cost.

Conclusion

C1E2D00 — RCTB Signal Communication Timeout — is a BYD manufacturer-controlled chassis code that signals a breakdown in CAN network communication involving BYD’s proprietary RCTB signal. Like all communication timeout faults, it is a reporting code: it tells you that a module stopped receiving an expected input, not definitively why. The most productive diagnostic path begins with 12V auxiliary battery condition, moves through wiring and connector integrity on the affected CAN segment, checks termination resistance, and advances to module-level oscilloscope testing only after those simpler causes have been eliminated. Given BYD’s EV and PHEV architecture — high network complexity, numerous interdependent modules, and a relatively small auxiliary battery managing all of it — supply-side and wiring faults are disproportionately common triggers for what initially appear to be module-level communication failures. Methodical, evidence-led diagnosis almost always produces a faster and less expensive outcome than chasing module replacements before the root cause is confirmed.