Testing lambda probe heating -Z19 and -Z29 at lambda probes (before and after catalytic converter) — AUDI

APP AQA ARZ
Special tools and workshop equipment required

V.A.G 1526 A
V.A.G 1594 A
V.A.G 1598/31

Requirements for test:

Coolant temperature at least 80 °C
Fuse for lambda probe heating OK

=> Current flow diagrams, Electrical fault finding and Fitting locations

Fuel pump relay OK. Testing => Page
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Note:

The lambda probe heating for lambda probes before and after catalytic converter receives its voltage supply via the fuel pump relay.

Test sequence

Remove connector cover -arrows-.

Unplug 4-pin connector (black) for lambda probe (before catalytic converter) -G39.

Not on vehicles with engine code letters AJQ, AQA:

Unplug 4-pin connector -1- (brown) for lambda probe (after catalytic converter) -G130.

All models

Connect multimeter (resistance measurement range) between contacts 1 and 2 of the corresponding connector.
Specification: 1 ... 5 ω(at room temperature)

Note:

The resistance will increase sharply at higher temperatures.

If the specification is not attained:

Renew the lambda probe.

If the specification is obtained:

Test voltage supply for lambda probe heating.

Testing voltage supply for lambda probe heating

Connect multimeter (voltage measurement range) between contacts 1 (positive) and 2 (earth).
Start the engine.
Specification: approx. battery voltage (may fluctuate)

Notes:

At certain points during operation, the engine control unit intervenes by constantly connecting and disconnecting the earth connection for lambda probe heating. For this reason the voltage displayed on the tester may fluctuate.
If required, observe Display Group 041 in the "Read measured value block" function to find out when the engine control unit is switching the lambda probe heating on and off.

If no voltage is present:

Connect multimeter (voltage measurement range) as follows:

Connector / Contact · Measure against
1 (positive) · Vehicle earth

Operate starter briefly.
Specification: approx. battery voltage

If there is still no voltage reading:

Test for open circuit in wiring from contact 1 to fuel pump relay via fuse.

=> Current flow diagrams, Electrical fault finding and Fitting locations

If the voltage supply is OK:

Connect multimeter (voltage measurement range) as follows:

Connector / Contact · Measure against
2 (switched earth / connection for engine control unit) · Battery positive

Start the engine.
Specification: approx. battery voltage (may fluctuate)

Switch off ignition.

If no voltage is present:

Connect test box V.A.G 1598/31 to wiring harness for engine control unit. Do not connect to the engine control unit itself.
=> Page
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Test for open circuits in the following wiring connection:

Lambda probe heater -Z19 for lambda probe before catalytic converter (black connector):

Connector / Contact · Test box V.A.G 1598/31 / Socket
2 · 5

Lambda probe heater -Z29 for lambda probe after catalytic converter (brown connector; not on vehicles with engine code letters AJQ, AQA):

Connector / Contact · Test box V.A.G 1598/31 / Socket
2 · 63

Rectify any open circuits.

If the wiring connection is O.K. but the lambda probe heating still has no earth connection:

Fit a new engine control unit => Page
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