Volkswagen Workshop Service and Repair Manuals > Golf Mk4 > Engine | 4-cylinder injection engine (1.6 l engine) Mechanics | Engine cooling | Removing and installing parts of cooling system | Checking map-controlled engine cooling thermostat

Checking map-controlled engine cooling thermostat

Special tools and workshop equipment required

t	Fault reader -V.A.G 1551- or vehicle system tester -V.A.G 1552- with diagnosis cable -V.A.G 1551/3C-

t	Adapter lead, 121-pin -V.A.G 1598/31-

t	Hand multimeter -V.A.G 1526C- or multimeter -V.A.G 1715-

t	Adapter set -V.A.G 1594C-

Test procedure

l	Engine must be cold.

–	Pull 2-pin connector off map-controlled engine cooling thermostat.

–	Measure resistance of heater element of map-controlled engine cooling thermostat using adapter cables from auxiliary measuring set -V.A.G 1594C-. Specification at 25 °C: 14...16 Ω.

If the specification is not obtained:

–	Renew map-controlled engine cooling thermostat -F265-.

If the specification is attained:

–	Connect fault reader -V.A.G 1551- (vehicle system tester -V.A.G 1552-). Start engine and select “Address word” 01 of engine control unit. Connect fault reader and select engine control unit → Rep. Gr.01.

Indicated on display:

–	Press keys 0 and 8 for function “Read measured value block” and confirm entry with Q key.

Rapid data transfer                 HELP

Select function XX

Indicated on display:

–	Press keys 1, 3 and 1 for “Display group number 131” and confirm entry with Q key.

Read measured value block           Help

Input display group number XXX

Indicated on display: (1...4 = display zones)

–	Connect multimeter to measure voltage at contacts 1 and 2 of 2-pin connector for thermostat (wiring harness side)

Read measured value block 131          -

         1         2         3         4

–	Pull 4-pin connector -1- off coolant temperature sender -G62--2-.

–	Allow engine to continue to run at idling speed and observe the left "bit" in display zone 4: if after a couple of seconds a “1” is displayed (fault detected) the duty cycle of the thermostat must change to 100% in display zone 3.

–	Now read voltage on multimeter. Specification: approx. alternator voltage.

If the specification is attained:

–	Reconnect 4-pin connector to coolant temperature sender -G62- again.

–	Check functions of thermostat → Chapter.

If the specification is not attained:

–	Switch engine off.

–	Connect multimeter to measure voltage to contact 1 of 2-pin connector and earth.

–	Switch on ignition. Specification: at least 11.5 V

If the specification is not attained:

–	Check wiring/connections to current supply relay for Simos engine control unit (in protective housing for relays in engine compartment) → Current flow diagrams, Electrical fault finding and Fitting locations

If the specification is attained:

–	Switch off ignition.

–	Connect 121-pin adapter cable -V.A.G 1598/31- to control unit wiring harness. The engine control unit remains disconnected.

–	Check wiring between test box and 2-pin connector for open circuit referring to current flow diagram. Contact 2 and test box socket 116, wiring resistance: max. 1.5 Ω.

–	Additionally check wire for short circuit to battery positive and earth. Specification: ∞ Ω.

If no fault can be detected in the wiring and the resistance of the thermostat heating element is OK. Check function of thermostat as follows:

Volkswagen Workshop Service and Repair Manuals