Volkswagen Workshop Service and Repair Manuals

Special tools, testers, measuring instruments and auxiliary items required

• ◆ Fault reader V.A.G 1551 or vehicle system tester V.A.G 1552 with cable V.A.G 1551/3
• ◆ Test box V.A.G 1598/18
• ◆ Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
• ◆ Adapter set V.A.G 1594
• ◆ Current flow diagram

Note:

The engine control unit will use the intake air temperature as a replacement value for an engine start (start temperature replacement value) as soon as there is a fault stored in the fault memory, which affects the coolant temperature sender (G62). The temperature then rises according to a model stored in the control unit. When the engine has reached normal working temperature a fixed replacement value will be displayed after a certain period. This fixed value is also dependent upon the intake air temperature.

Test sequence

• ‒ Connect the fault reader V.A.G 1551 (V.A.G 1552). Then switch ignition on and select engine control unit with the "Address word" 01.
  (Connecting fault reader and selecting engine control unit .)

• ‒ Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.

• ‒ Press keys 0, 0 and 1 for "Display group number 1" and confirm entry with Q key.

• ‒ Check whether the coolant temperature is above 85 °C in display zone 2.
• ‒ Press C key.
• ‒ Press keys 0, 0 and 3 for "Display group number 3" and confirm entry with Q key.

• ‒ Read off coolant temperature value in display zone 3.

     1)     If a temperature is displayed which deviates greatly from the ambient temperature of the sender, check sender wiring for transfer resistances.

     2)     Check is only possible when the engine is cold.

Continuation of check when display approx. -46 °C:

• ‒ → Pull 2 pin connector -arrow- off coolant temperature sender.

• ‒ → Bridge connector contacts 1+2 using aux. cables from V.A.G 1594 and observe display.

Display approx. 141 °C:

• ‒ Press ⇒key.
• ‒ Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
• ‒ Switch off ignition.
• ‒ Renew coolant temperature sender (G62).

Display -46 °C:

• ‒ Press ⇒key.
• ‒ Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
• ‒ Switch off ignition.
• ‒ → Connect test box V.A.G 1598/18 to control unit wiring loom.
• ‒ Check wire between test box socket 14+2 pin connector contact 1 for open circuit using current flow diagram.
       Wire resistance: Max. 1.5 ω
• ‒ Check wiring additionally for short circuit to battery positive.
       Specification: ∞ω
• ‒ Check wire between test box socket 33+2 pin connector contact 2 for open circuit according to current flow diagram.
       Wire resistance: Max. 1.5 ω

If no fault in wire is detected:

• ‒ Renew engine electronics control unit => Page 24-115 .

Continuation of check when display approx. 141 °C:

• ‒ → Pull 2 pin connector -arrow- off coolant temperature sender.

Display -46 °C:

• ‒ Press ⇒key.
• ‒ Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
• ‒ Switch off ignition.
• ‒ Renew coolant temperature sender (G62).

Display approx. 141 °C:

• ‒ Press ⇒key.

• ‒ Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
• ‒ Switch off ignition.
• ‒ Pull connector off engine control unit.
• ‒ → Pull 2 pin connector -arrow- off coolant temperature sender.
• ‒ Check wire between control unit connector and 2 pin connector contact 2 for short to contact 1 wire and to vehicle earth, according to current flow diagram.
       Specification: ∞ω

If no fault in wire is detected:

• ‒ Renew engine electronics control unit => Page 24-115 .

Continuation of check when display approx. coolant temperature:

Test conditions

• ● Engine must be cold.

Functional check of sender

• ‒ Connect fault reader V.A.G 1551 (V.A.G 1552). Start engine and select "Address word" 01 of engine control unit. When doing this the engine must be running at idling speed.
  (Connecting fault reader and selecting engine control unit => Page 01-5 .)

• ‒ Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.

• ‒ Press keys 0, 0 and 1 for "Display group number 1" and confirm entry with Q key.

• ‒ With engine running observe coolant temperature value in display zone 2. The temperature figure must
       increase uniformly and without interruption.

Notes:

• ◆ If the display on fault reader jumps by 2...5 °C, it is a control unit fault and not caused by a defective sender.
• ◆ If irregular engine running occurs in certain temperature ranges and the temperature figure does not increase without interruption, the temperature signal is temporarily interrupted and the sender must be renewed.

• ‒ Press ⇒key.
• ‒ Press keys 0 and 6 for the function "End output" and confirm entry with the Q key.