HVCH Not Starting? Check Low-Voltage Supply and Wake-Up

During vehicle testing, it is truly dreadful to encounter a cold morning only to find that the heater will not start. The vehicle’s control unit sends a command to heat the system, yet the coolant remains ice-cold. In such situations, people often jump to the conclusion that the heater is faulty. However, in our experience, this assumption is usually incorrect; blindly replacing the heater not only wastes a week’s time, but the true root cause of the fault remains in the vehicle, unresolved.

When a high-pressure coolant heater fails to start, the cause can usually be attributed to one of the following three categories: the ‘communication protocol’ expected by the vehicle does not match the heater’s design; the heater did not receive a ‘wake-up’ or ‘enable’ signal during the start-up attempt; the controller is operational but the heating function is locked (not authorised to activate); or the problem lies with the thermal system rather than the electrical system. Troubleshooting in this order is far more efficient than simply carrying out a single measurement.

Firstly, check whether the wrong model has been selected

Troubleshooting should begin with model selection, rather than immediately resorting to a multimeter. Our B-series and E-series products appear very similar in the EVLINK specification summary table, both with power ratings of 20–24 kW and voltage ranges of 400–800 V. If one looks only at the power parameters, the two are indeed identical; however, a glance at the ‘Control Method’ column reveals the difference: the B Series supports CAN communication and is equipped with an enable interface, whilst the E Series utilises thermostat control, supporting neither CAN communication nor an external control interface.

Assuming a project requires the vehicle controller to issue heating commands and read the heater’s status information via the CAN bus, the B Series would be the appropriate option to consider; the E Series, however, cannot meet these communication requirements. This constitutes a case of incorrect product selection, which should be resolved prior to commissioning, rather than being misinterpreted as a CAN communication fault in the E Series heater.

Even if the correct series has been selected, one point must be noted: the description ‘CAN communication + enable’ does not in itself include specific pin definitions, message identifiers, wake-up sequences or diagnostic definitions. These details are all contained in the ‘Interface Specification Document’ for the specific model. We cannot simply apply parameters from the manuals of other heater models to fill in this information. Even if the power rating is the same, the wiring methods or software logic between different models are not interchangeable.

Secondly, examine the actual input conditions at the moment of start-up failure

Next, please focus on the actual input signals at the precise moment of start-up failure, rather than the status several minutes later. Reading voltage values several minutes after an intermittent start-up failure has occurred is of very limited value for analysing the circumstances of the start-up attempt at that time.

Here, a simple arithmetic deduction can be made—and it is merely arithmetic. Suppose a heater draws 22 kW of power from a 600 V DC power supply; under these conditions, the current would be 22,000 divided by 600, which is approximately 36.7 A. This figure is not derived from actual current measurements taken from the EVLINK heater. It does not prove whether the control electronics received the required power supply, nor does it prove that commands were received, nor does it prove that the heater is capable of delivering 22 kW of power across its entire operating voltage range. Furthermore, this does not constitute a recommendation for the selection of cables or fuses; such decisions must be based on the actual limit parameters of the selected equipment and the vehicle’s electrical design.

We require the engineer in charge to record more specific details: the status of the control power supply at the specified monitoring points, along with the ‘wake-up’ or ‘enable’ input signals, and any information actually fed back by the specific model of the device. Please ensure that the temporal relationships between the various signals are preserved. For example: had the unit already entered the prescribed ‘ready’ state prior to the heating request? Did a change in the power supply status or vehicle status occur precisely at the moment the start-up attempt failed? Specific timing requirements should comply with the published interface specifications. If data for a particular channel has not been collected, please indicate ‘not recorded’. This is far more valuable than speculating on a ‘plausible’ value after the event.

Thirdly, distinguish between a ‘suppressed controller’ and a ‘thermal management issue’

The controller may be active, yet the heating function may still be suppressed. Refer to the relevant technical documentation for the heater and the vehicle to clarify which conditions trigger suppression and which states can be monitored. When analysing alarm conditions or situations where the heating function fails to activate, judgements should be made based on these definitions; under no circumstances should all ‘suppressed’ states be regarded as internal hardware faults.

If a ‘Ready’ signal is not defined in the system model, do not invent one. For devices managed by a thermostat, the established control architecture must be followed. If the heater itself does not support CAN communication, the fact that the CAN bus data log is empty does not prove that the heater is faulty.

Even if the electrical inputs are normal, thermal management issues must still be considered separately. Coolant flow rate, initial temperature, circuit heat capacity, sensor location and observation duration all influence the interpretation of temperature change curves. Please refer to the existing High-Voltage Heater (HVCH) Power Verification Guidelines to distinguish between the following three easily confused concepts: requested output power, electrical input power and actual heat output.

When troubleshooting ‘failure to start’ faults, a clear analytical approach must be maintained. First, confirm whether the start-up and heating conditions specified in the technical documentation have been met. If the unit is receiving power but the coolant temperature response is abnormal, proceed to investigate thermal management whilst retaining the electrical observation data. Under no circumstances should communication settings be repeatedly altered in an attempt to resolve unverified issues with the water or thermal circuits.

Before performing any reset operations, ensure that evidence has been collected and organised.

Before resetting, be sure to save the original fault information. If the fault disappears after a restart, this result should be recorded alongside previous fault investigation attempts; under no circumstances should historical records simply be rewritten to state ‘no fault found’. Comparing successful and failed operating conditions often yields more valuable information than consulting technical manuals.

A valid set of evidence should include: heater model and software version, interface version, requested operating commands, observed power supply and operating statuses, and fault information. Furthermore, the measurement location should be noted, and any differences between different operating batches should be recorded.

Operations and measurements involving high-voltage systems must be carried out by appropriately qualified personnel, in strict compliance with the vehicle manufacturer’s isolation and maintenance procedures. It is strictly prohibited to bypass interlock devices, forcibly activate power stage circuits, apply unverified test voltages, or use unconfirmed connector pin definitions. The purpose of such troubleshooting is to determine reasonable directions for further investigation, not to conduct arbitrary live-circuit testing.

What information to provide to EVLINK

When contacting EVLINK regarding HVCH (High-Voltage Coolant Heater) integration, please provide the exact heater model, the vehicle’s voltage range, the required control method, and any existing records of start-up events. Please specify which of the following scenarios applies to the specific issue: a lack of start-up response, the system returning an ‘inhibit’ signal, or the occurrence of unexpected thermal management results. This will enable us to determine which product documentation and project inputs are required for further discussion.

Regarding network mapping, please refer to the dedicated ‘HVCH CAN Integration Checklist’, which covers a broader range of interface tasks. Our range of coolant heaters is available for your selection. Please do not adapt descriptions intended for the entire product range into customised communication protocols for a specific individual unit without authorisation.