Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Residual heater
This function can be ordered as an accessory. See Reading off vehicle configuration data to check whether the car has a residual heater.
The function is activated in the driver information module (DIM) (5/1) using the control stalk (compare to the parking heater). Information about activation is sent to the central electronic module (CEM) (4/56) and climate control module (CCM) (3/112). The blower fan and damper settings are set by the climate control module (CCM). The central electronic module (CEM) transmits data to the combustion preheater module (CPM) (4/7) instructing it to activate the water pump.
When the residual heater is activated it will operate as long as the coolant temperature is above 30 °C or for a maximum of 20 minutes or until the function is switched off.
This function is used when the coolant is already warm. The coolant pump is started thereby circulating the coolant. The heat is distributed from the coolant to the passenger compartment unit in the climate control unit and on to the passenger compartment.
When the residual heater is running, the passenger compartment is heated by the climate control module (CCM) controlling the fan and damper according to a customer parameter (Applies only to electronic climate control (ECC)). This parameter is used to set the distribution between the defroster and the floor. The normal setting is 30% defroster and 70% floor.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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