Volkswagen Workshop Service and Repair Manuals

Special tools, workshop equipment, 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 1598/22
• ◆ 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 conditions

• ● Engine must be cold.

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 4 for "Display group number 4" and confirm entry with Q key.

• ‒ Read off coolant temperature value in display zone 3.
       Specification: approx. coolant temeprature

If the specification is not obtained:

• ‒ Perform check according to following table:

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

If the specification is obtained:

• ‒ Start engine and run at idling speed.
  The temperature value must
       increase uniformly

Notes:

• ◆ Temperature rises in steps of 1.5 °C.
• ◆ 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.

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

• ‒ → Pull 4 pin connector -1- off coolant temperature sender (G62) -2-.
• ‒ Bridge connector contacts 1+3 using aux. cables from V.A.G 1594 and observe display.

If display jumps to 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).

If display remains at approx. -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.
• ‒ Check wiring using current flow diagram
  => Page 24-52

Continuation of check when display approx. 141 °C:

• ‒ → Pull 4 pin connector -1- off coolant temperature sender (G62) -2-.

If display jumps to approx. -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).

If display remains at 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.
• ‒ Check wiring using current flow diagram
  => Page 24-52

Checking wiring

• ‒ → Connect test box V.A.G 1598/22 to control unit wiring harness.

• ‒ → Pull 4 pin connector -1- off coolant temperature sender (G62) -2-.
• ‒ Check wire between test box socket 67 and 4-pin connector contact 1 for open circuit using current flow diagram.
       Wire resistance: Max. 1.5 ω
• ‒ Check wire between test box socket 53 and 4-pin connector contact 3 for open circuit according to current flow diagram.
       Wire resistance: Max. 1.5 ω

• ‒ Check the wire between test box and 4 pin connector contact 1 for short to wire contact 3 and to vehicle earth using current flow diagram.
       Contact 3+socket 67
       Contact 3+vehicle earth
       Specification: ∞ω
• ‒ Additionally check both wires for short to battery positive.
       Specification: ∞ω

If no fault in wire is detected:

• ‒ → Perform resistance measurement on coolant temperature sender (G62) contact 1 (earth) and 3 (signal).

→ Scale A shows resistance values for temperature range 0...50 °C and scale B the values for temperature range 50...100 °C.

Examples:

• ◆ 30 °C is in range A and corresponds to a resistance of 1.5...2.0 kω
• ◆ 80 °C is in range B and corresponds to a resistance of 275...375 ω

If the specification is not obtained:

• ‒ Renew coolant temperature sender (G62) => Page 24-3 , item 12 .

If there is no fault in the wiring and the resistance measurement values are OK.:

• ‒ Renew engine electronics control unit => Page 24-114 .