Repairing auxiliary heater -B4W- / -D4W- — VW
Repairing auxiliary heater -B4W- / -D4W- on VW: factory workshop procedure. Full factory text, tools and checks.
Workshop procedure for VW — the factory write-up, straight from real workshop data.
📋 Procedure
Repairing auxiliary heater -B4W- / -D4W-
Before beginning repair work, perform the following steps:
Disconnect battery
Rep. Gr.
27
.
Note
Before starting electrical welding work on the vehicle, disconnect the positive pole from the battery and connect it to earth in order to protect the
heater control unit
J162
.
A manufacturer's plate is attached to the heater unit. This plate gives details of the heater unit type installed in the vehicle
Fig.
.
The coolant circuit must be bled before testing work and after it is opened
Chapter
Metering pump
V54
Checking fuel supply to auxiliary heater -B4W- or -D4W-
Chapter
.
In some cases, the metering pump might tick audibly but still does not deliver fuel because there is air in the intake connecting pipe. The
heater control unit
J162
will then switch off permanently.
The
diagnostic tester
5019
specifies the fault code 052. Please erase the fault code and switch the heater -B4W-/ -D4W- on several times.
Heater unit -B4W- / -D4W-
With
heater control unit
J162
Removing and installing
Chapter
Dismantling and assembling
Chapter
Exhaust pipe
Circulation pump
V55
This
circulation pump
V55
is only installed if the vehicle engine does not have a
continued coolant circulation pump
V51
.
Coolant hoses
Coolant hose routing; connecting auxiliary heater to coolant circuit
Chapter
.
Ambient temperature switch
F38
Switch position
“on”
at temperatures below 5
o
C
Switch position
“off”
at temperatures above 5
o
C
Part number 701 959 625
Manufacturer's plate
Note
The most important technical data are shown on upper part of manufacturer's plate.
The date of first use is entered on the lower part of manufacturer's plate.
Version -B4W- for petrol: 20 1760; version -D4W- for diesel: 25 1950.
The year the unit was first put into use must be entered on the
“Genuine part”
manufacturer's plate. The heat exchanger for the auxiliary heaters does not have to be renewed after 10 years. Legislation in Germany dictates that air heaters must be renewed.
The manufacturer's plate must be attached at a clearly visible location, e.g. on the lock carrier.
TorqFix answers live for your specific car — tell it the engine code and it serves the matching sequence, torque figures and wiring for that exact variant.
Ask about my car →Other VW procedures
Who makes these pages, and how
TorqFix was built by a mechanic — after a 2,700 km drive with five roadside repairs that no diagnostic tool could explain.
The figures on this page come from manufacturer workshop documentation and are shown as they are. The page is assembled automatically from that data — it is not written by an AI. The AI works in the chat, where it answers for your specific car. It writes nothing here.
Variants of the same model differ. Cross-check torque against the factory manual for your engine before final tightening.
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The story behind TorqFix →Workshop data on this page last updated 20 Sep 2026.