Testing power steering pressure switch -F88: Audi 1.8 (AJQ, APP, APX, APY, …)

Special tools and workshop equipment required

V.A.G 1526 A
V.A.G 1594 A
V.A.G 1598/31
VAS 5051 with VAS 5051/1

or

V.A.G 1551 with V.A.G 1551/3 A

The function of the power steering pressure switch is to stabilise the idling speed when the steering wheel is on full lock (left or right).

Test sequence

Connect vehicle diagnostic, testing and information system VAS 5051 (or fault reader V.A.G 1551) and select engine electronics control unit by entering address word "01" ( => Page
01-3
.)
When doing this the engine must be idling.

Rapid data transfer
HELP
Select function XX
Indicated on display:

Enter "08" to select the function "Read measured value block" and confirm entry with Q key.

Read measured value block
Q
Enter display group number XXX
Indicated on display:

Enter "056" for Display Group 056 and confirm entry with Q key.

Read measured value block
56
⇒
1
2
3
4
Indicated on display:

Check display value for power steering pressure switch (display zone 4).

Display zones
1 · 2 · 3 · 4
Display Group 056: Idling speed stabilisation with engine idling at normal operating temperature
Display · xxx rpm · xxx rpm · x.x % · X X X X X
Indicates · Actual engine speed · Specified engine speed · Idling speed control / Torque change · Operating status
Range · / · 0XXXX / 1XXXX
Specification · 0XXXX / (steering wheel in straightahead position or slightly turned)
1XXXX / (steering wheel / at full lock, or turned rapidly)
Note · X = irrelevant

If the display values do not appear as described:

Testing switch

Unplug connector from power steering pressure switch -F88 on power steering pump.

Connect multimeter to switch (resistance measurement range).
Start the engine.
Specification: ∞ ω (no continuity)

Turn steering wheel to full lock (left and right).
Specification: approx. 0 ω

If the display does not change:

Renew power steering pressure switch -F88.

If the display changes:

Test the wiring => Page
24-169
.

Testing wiring

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
24-16
.

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

Connector / Contact · Test box V.A.G 1598/31 / Socket
1 · 49
2 · 50

Rectify short circuit or open circuit if necessary.