Checking air mass meter -G70 with CO-potentiometer -G74 for control unit-Nr. 4A0 906 266/A/AA/AB (ä 08.92) — AUDI

Special tools, testers and workshop equipment required

V.A.G 1526 A
V.A.G 1527 B
V.A.G 1594 A
V.A.G 1598 A
V.A.G 1598/11

Installation position => Installation position overview - Page
24-6

Note:

Checking operation=> Basic setting, display group 000, display zone 2, Page
01-75
.

Test requirements:

Fuse S74 (in red holder -1- in passenger-side footwell electronics box) OK.

Note:

Use only gold-plated contacts when repairing the contacts in the plug connectors.

Checking power supply

Pull connector off air-mass meter.
Connect voltage tester V.A.G 1527 B as follows:

Connector / Contact · Measure to
3 · Engine earth

Switch the ignition on.
The LED must illuminate.

If the LED does not illuminate:

Check the wiring between contact 3 of connector and fuse for open circuit/short to earth and repair if necessary.

=> "Current Flow Diagrams, Electrical Fault Finding and Fitting Locations" binder

Checking earth supply

Pull connector off air-mass meter.

Connect voltage tester V.A.G 1527 B as follows:

Connector / Contact · Measure to
2 · Battery positive

The LED must illuminate.

If the LED does not illuminate:

With ignition switched off, use adapter V.A.G 1598/11 to connect test box V.A.G 1598 A to engine control unit connector A only (control unit remains disconnected) => Page
24-17
.

Check for open circuit and short to positive or earth in the following wiring connections:

Connector / Contact · Test box V.A.G 1598 A / Socket
2 · 45

Rectify any open/short circuit as necessary.

=> "Current Flow Diagrams, Electrical Fault Finding and Fitting Locations" binder

Checking signal wiring for air mass meter

With ignition switched off, use adapter V.A.G 1598/11 to connect test box V.A.G 1598 A to engine control unit connector A only (control unit remains disconnected) => Page
24-17
.

Check for open circuit and short to earth/positive or earth in the following wiring connections:

Connector / Contact · Test box V.A.G 1598 A / Socket
1 · 42
4 · 41

Rectify any open/short circuit as necessary.

=> "Current Flow Diagrams, Electrical Fault Finding and Fitting Locations" binder

Checking signal voltage

Test requirements:

Wiring OK
Air mass meter connected
Electrical consumers switched off (radiator fan must not run during the test)

Push back rubber grommet at connector of air mass meter

Note:

Pin assignment is marked on back of connector.

CO potentiometer:

Connect multimeter to contacts 2 and 4 of air mass meter connector to measure the voltage.
Switch the ignition on.
Specification: 1.0 ... 7.5 V

If the specification is not obtained:

Replace air mass meter.

Air mass meter:

Connect multimeter to contacts 1 and 2 of air mass meter connector to measure the voltage.
Switch the ignition on.
Specification: 0.3 ... 1.1 V

Start engine and run at idling speed.
Increase engine speed and observe change in voltage.
Specification:
With increasing engine speed, and thus increasing air throughput, signal voltage increases proportionally up to approx. 3.4 V at 4000 rpm.

If voltage does not change, or if voltage dips with increasing engine speed:

Replace air mass meter.