Heater Check

Oxygen Sensor Heater For Oxygen Sensor, Checking


NOTE: The oxygen sensor heating circuit is monitored by the On Board Diagnostic (OBD). Check DTC memory.


- Connect vehicle diagnostic, testing and information system VAS5051 or VAG1551 scan tool and select engine electronics control module by entering address word "01". When doing this the engine must be at idle. [1][2]Scan Tool Connecting and Initial Checks

Indicated on display


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -8- to select function "Read Measuring Value Block" and confirm entry with -Q- button.

Indicated on display


Read Measuring Value Block
Input display group number XXX


- Press buttons -0-, -4- and -1- to select "display group number 041" and confirm entry with -Q- button.

Indicated on display


Read Measuring Value Block 41 ->
1 2 3 4


- Adjust engine speed to approx: 3000 RPM
- Check resistance of oxygen sensor heater.

Display Group 41:

- Press -C- button.
- Press buttons -0-, -4- and -2- to select "display group number 042" and confirm entry with -Q- button.

Display Group 42:

If the specification is not attained:
- Check voltage supply for oxygen sensor heater.
- Check oxygen sensor signal wire and activation.

Checking voltage supply for oxygen sensor heater

- Check fuse for oxygen sensor heater
- Disconnect 4-pin harness connector of particular oxygen sensor.







- Connect hand-held multimeter (voltage measurement range) between sockets 1 (B+) and 2 (Ground (GND)) using test leads from VAG1594 connector test kit.
- Operate starter briefly.

Specified value: approx. battery voltage

If there is no voltage reading:
- Connect hand-held multimeter (voltage measurement range) between socket 1 (B+) and vehicle Ground (GND) using test leads from VAG1594 connector test kit.
- Operate starter briefly.
Specified value: approx. battery voltage

If there is still no voltage reading:
- Check for open circuit and/or short circuit in wiring between fuel pump relay and socket 1 on the relevant oxygen sensor connector (on wiring harness) via fuse.
If the voltage supply is OK:







- Connect hand-held multimeter (voltage measurement range) between socket 2 (switched Ground (GND) connection from engine control module) and B+ terminal using test leads from VAG1594 connector test kit.
- Start engine.

Specified value: approx. battery voltage (fluctuating)


NOTE: At certain points in the operating range the engine control module continuously "switches" the Ground (GND) connection to the oxygen sensor heater. That means, it repeatedly connects and disconnects the Ground (GND) connection at these points. For this reason the voltage reading on the tester may fluctuate.


- Switch ignition off.

If there is no voltage reading:
- Connect VAG1598/31 test box to wiring harness for engine control module. Do not connect to the engine control module itself.







- Check for open circuits in the following wiring connection:







Resistance in wiring: max. 1.5 Ohm

If the wiring is OK but the oxygen sensor heater still has no Ground (GND) connection:
- Replace particular oxygen sensor.
- Display readiness code. The readiness code must be generated if the DTC memory was erased. Readiness Code Reading Readiness Code, Generating