Checking the Coolant Temperature Sender: VW (AGL, AUH)

Special tools, workshop equipment, test and measuring equipment and accessories required

Fault output device V.A.G 1551with cable V.A.G 1551/5
Testing box V.A.G 1598/30
Hand-held multimeter V.A.G 1526 or Multimeter V.A.G 1715
Measuring aids set V.A.G 1594
Current flow diagram

Testing Procedure

Connect the fault output device V.A.G 1551and use the "Address word" 01 to select the control unit for engine electronics. Here, the engine must be idling.
(Connecting fault reader and selecting engine electronics control unit => page
01-4
.)

Fast data interchange
HELP
Select function XX
Display:

Press the keys 0 and 8 for the function "Read measurement value block" and confirm the input using the Q key.

Read measurement value block
HELP
Enter display group number XXX
Display:

Press buttons 0, 0 and 7 for "Display group number 7" and confirm entry with Q button.
Read measured value block 7
⇒
15.9 5C
16.7 5C
Display:
Check the coolant temperature value in display field 4. The temperature value must
rise evenly without interruption.
If there is no realistic display in display field 4 or if a replacement temperature of approx. -20°C is displayed, check the coolant temperature sender and the cable connections to the sender as follows:
Press the ⇒key.

Press the keys 0 and 6 for the function "Quit data interchange" and confirm the input using the Q key.
Switch the ignition off.
Remove the connector from the sender => Installation Points Overview, page
23-5
.
Measure resistance between contacts 1+3 on sender.

Setpoint value, see diagram

Area A shows you the resistance values for the temperature range 0...50°C; area B shows the values for the temperature range 50...100 °C.

Readout examples:

30 °C corresponds to a resistance of 1500...2000 ω
80 °C corresponds to a resistance of 275...375 ω

If the setpoint value is not reached:

Replace the coolant temperature sender (G62).

If the setpoint value is reached:

Connect the testing box V.A.G 1598/30 to the control unit wiring loom. The engine control unit is not connected in the process.

Check wires between test box and 4-pin connector for breaks using current flow diagram.
Contact 1+socket 3/28
Contact 3+socket 3/32
Cable resistance: max. 1.5 ω
Also check the cables for short-circuit among themselves, to the vehicle earth or the battery positive terminal.
Setpoint value: ∞ω

If not fault in the cables is discovered:

Replace the control unit for diesel direct injection system (J248) =>page
23-61
.