Combustion Air Blower Short Circuit to Ground – Parking Heater Faulty – Compramas

In short: The fault “combustion air blower – short circuit to ground” usually means the control unit inside the heater can no longer activate the blower correctly. The parking heater then does not start, or the blower runs permanently and drains the battery. A new blower alone does not help – but the heater can be repaired or replaced with a refurbished exchange unit.

Your parking heater or auxiliary heater no longer works and the fault memory shows the message “Combustion air blower – short circuit to ground”? With this well-known fault, the cause lies in the heater's control unit.

Due to the defect, the control unit can no longer activate or switch off the combustion air blower properly. Depending on the severity, the parking heater no longer starts, aborts the heating process, or the combustion air blower keeps running permanently. This can heavily discharge or completely drain the vehicle battery.

What does “combustion air blower short circuit to ground” mean?

The combustion air blower supplies the heater with the necessary combustion air during operation. Activation, speed control and switch-off of the blower are handled by the control unit built into the heater.

If the electronic activation in the control unit is faulty, the combustion air blower can no longer be controlled correctly. The heater detects an electrical malfunction and stores the fault:

Combustion air blower – short circuit to ground

Depending on the heater, vehicle and diagnostic system used, similar fault descriptions may also be displayed:

Combustion air fan short circuit to ground
Combustion air blower electrical malfunction
Combustion air blower activation faulty
Blower motor short circuit to ground
Combustion air blower open circuit or short circuit
Parking heater combustion air blower fault

With this fault, the control unit of the parking heater or auxiliary heater is faulty.

Typical symptoms of this heater fault

The fault “combustion air blower short circuit to ground” can show itself in different ways:

The parking heater no longer starts
The auxiliary heater does not work
The heater aborts the start process
The parking heater goes straight into fault mode
The combustion air blower is not activated
The fault can be cleared but reappears
The heater is locked after several start attempts
The combustion air blower runs permanently
The blower does not switch off after switching off
The parking heater causes increased quiescent current
The vehicle battery is discharged
The vehicle no longer starts after standing for a long time

Which symptoms occur depends on how the defect affects the blower activation in the control unit.

Combustion air blower runs permanently and does not switch off

A particularly noticeable fault is when the combustion air blower runs constantly, even though the parking heater has been switched off or the vehicle is no longer in use.

Due to the defect in the heater control unit, the output for the combustion air blower can remain permanently activated. The blower continues to be supplied with voltage and can no longer be switched off via normal operation.

Typical signs of this problem are:

audible blower noise when the vehicle is switched off
the parking heater keeps running on
combustion air blower only stops after the power supply is interrupted
repeatedly discharged vehicle battery
increased quiescent current
battery is flat after standing for a short time

Since the combustion air blower consumes power continuously, the vehicle battery can be heavily discharged. In the worst case, the vehicle can then no longer be started.

The heater should therefore be checked promptly.

Why does the parking heater no longer start?

If the electronic activation of the combustion air blower in the control unit is damaged, the blower may no longer be able to be switched on or controlled.

Since the necessary combustion air is missing, the heater cannot carry out the start process properly. The parking heater aborts the heating process and stores the corresponding fault code.

Depending on the number of unsuccessful start attempts, the heater may also lock itself. After the defect has been fixed, unlocking or clearing the fault memory may therefore be required.

Is the combustion air blower itself faulty?

The fault message “combustion air blower short circuit to ground” does not automatically mean that the blower motor itself has to be replaced.

Before the repair, the combustion air blower and the associated vehicle electrics should nevertheless be checked. This includes in particular:

combustion air blower or blower motor
electrical wiring
connectors
power supply
ground connections
fuses
possible moisture or corrosion

If the combustion air blower and wiring are fine, the cause of this well-known fault lies in the heater's control unit.

Replacing the combustion air blower alone does not fix the control unit defect.

What consequences can the defect have?

In addition to the failure of the parking heater, a faulty heater control unit can have other effects.

If the combustion air blower keeps running permanently, the vehicle battery is under constant load. In addition, the heater may set a lockout due to several unsuccessful start attempts.

Possible consequences are:

complete failure of the parking heater
auxiliary heater not working
discharged vehicle battery
vehicle can no longer be started
heater is locked
recurring fault entry
additional diagnostic and workshop costs

The fault should therefore not be ignored for long.

Repair or exchange of the heater

For the fault “combustion air blower short circuit to ground” there are basically two solutions.

Repair of the existing heater

For a repair, the existing heater or the faulty control unit is sent in. The electronic activation of the combustion air blower is tested and the commissioned fault is repaired.

You then receive your own heater back.

Please note that the repair and the associated warranty relate to the fault area worked on. If a different, technically unrelated or age-related defect occurs later, this is a new repair case.

Exchange heater

Alternatively, the complete heater can be replaced by a tested or refurbished exchange unit.

An exchange can make particular sense if the heater is already older or further age-related defects cannot be ruled out. This may avoid later failures as well as repeated removal and installation costs.

Which offer suits your vehicle and heater depends, among other things, on the part number, the unit version and the availability of a suitable exchange unit.

What is needed for processing?

For a clear assessment we need details about the heater and the fault symptom that are as precise as possible:

vehicle manufacturer and vehicle model
model year
manufacturer of the heater
part number of the heater
stored fault code
exact description of the symptoms
information on whether the combustion air blower runs permanently

A helpful fault description would be, for example:

“The fault memory shows combustion air blower short circuit to ground. The combustion air blower keeps running permanently and does not switch off after the parking heater is switched off. This discharges the vehicle battery.”