Audi Workshop Service and Repair Manuals

A/C compressor shut-off

Notes:

• ◆ In order to ensure that the full engine power is available under acceleration, the A/C compressor is shut off for a few seconds via connection C11 on the Motronic control unit.
• ◆ Connection C11 on the Motronic control unit switches the positive signal coming from the air conditioner to ground and thus triggers the compressor shut-off.

Test requirements:

• ● Air conditioning functioning properly.
• ● No faults recorded in air conditioner fault memory
• ● Interior temperature of more than +15 oC

Procedure:

• ‒ Connect the fault reader V.A.G 1551
• ‒ Start engine
• ‒ Select "Read measured value block" (function 08) and Display group 20.

Specified value in Display zone 4 with the air conditioner switched off: Compr. OFF

• ‒ Switch the air conditioner on with the "Auto" button The compressor must run (ice crystal on the display of the A/C operating unit)

Specified value: "A/C Low" or "A/C High" in Display zone 3 and "Compr. ON" in Display zone 4

• ‒ Depress accelerator suddenly and release again (brief blip of throttle).

When the accelerator is floored quickly, the readout in Display zone 4 should jump from "ON" to "OFF" for a few seconds (compressor shut off during acceleration).

• ‒ → If the display is not as described, switch off the engine and connect test box V.A.G 1598/19 to the wiring harness for Motronic control unit -J220 .
• ‒ Test wiring from contact C11 at Motronic control unit to A/C operating unit (-E87) according to the current flow diagram for short to ground or positive or for open circuit.
• ‒ If no fault is present in the wiring check the function of the A/C operating unit (-E87).

=> Air conditioning; Repair Group 01; Self-diagnosis for air conditioning

Engine speed adaptation through switching on the air conditioner

Notes:

• ◆ A positive signal is applied to the connection C14 on the Motronic control unit when the air conditioner is switched on or the rear window heating is switched on.
• ◆ The signal causes the Motronic control unit to maintain a constant idling speed despite the varying power requirement of the air conditioner.
• ◆ On vehicles with an automatic gearbox the idling speed changes from approx. 860 rpm to approx. 780 rpm when a gear is engaged. Both engine speeds are kept constant when the air conditioner is switched on.

Test requirements:

• ● Air conditioning functioning properly.
• ● No faults recorded in air conditioner fault memory
• ● Interior temperature of more than +15 oC

Procedure:

• ‒ Connect fault reader V.A.G 1551 => Page 01-4.
• ‒ Start the engine (operating temperature)
• ‒ Switch off heated rear window
• ‒ Select Read measured value block (function 08) and Display Group 20.

Display zone 1: Idling speed

Display zone 3: Signal from air conditioner

Display zone 4: Signal from air conditioner compressor

• ‒ Switch the air conditioner on with the "Auto" button The compressor must run.

Specified value for Display zone 4: Compr. ENG"

Apart from a brief drop (less than 1 second) in rpm, the idling speed should remain constant.

If the engine speed is not kept constant, check whether the signal from the air conditioner is arriving at the Motronic control unit (Display zone 3).

Specified value for Display zone 3: "A/C Low" or "A/C High"

Specified value for Display zone 4: Compr. ENG"

• ‒ → If the signal is not arriving, switch off the engine and connect test box V.A.G 1598/19 to the wiring harness for the Motronic control unit .
• ‒ Check the wiring from contact C14 at the Motronic control unit to the A/C operating unit (-E87) according to the current flow diagram for open circuit or short circuit.
• ‒ If no fault is present in the wiring check the function of the A/C operating unit.

=> Air conditioning; Repair Group 01; Self-diagnosis for air conditioning

Engine speed adaptation through switching on the heated rear window

Notes:

• ◆ A positive signal is applied to the connection C14 on the Motronic control unit when the air conditioner is switched on or the rear window heating is switched on.
• ◆ The effect of this signal is that the Motronic control unit maintains idling speed at a constant level despite the additional load.
• ◆ On vehicles with an automatic gearbox the idling speed changes from approx. 860 rpm to approx. 780 rpm when a gear is engaged. Both engine speeds are kept constant when the heated rear window is switched on.

Procedure:

• ‒ Connect V.A.G 1551 .
• ‒ Start the engine (operating temperature)
• ‒ Switch off the air conditioner
• ‒ Select Read measured value block (function 08) and Display Group 20.

• ‒ Display zone 1: Idling speed
• ‒ Display zone 3: rear window heater signal

Note:

• ◆ As both the signal from the air conditioner and the signal from the heated rear window arrive at connection C14 of the Motronic control unit, Display zone 3 contains either "A/C Low" or "A/C High".

• ‒ Switching on the heated rear window

Apart from a brief drop (less than 1 second) in rpm, the idling speed should remain constant.

If the engine speed is not kept constant, check whether the signal from the heated rear window is arriving at the Motronic control unit (Display zone 3).

Specified value for Display zone 3: "A/C Low" or "A/C High"

• ‒ If the signal is not arriving, switch off the engine and connect test box V.A.G 1598/19 to the wiring harness for the Motronic control unit => Page 01-122.
• ‒ Connect diode test lamp between socket D11 (ground) and C14.
• ‒ Switch on ignition and rear window heater.

When the rear window heater is switched on, the diode lest lamp should come on.

• ‒ → If the diode test lamp does not light up, check the wiring between connection C14 on the Motronic control unit and the switch of the heated rear window according to the current flow diagram for open circuit.

Selector lever position of the automatic gearbox

Note:

• ◆ The multifunction switch -F125 on the gearbox switches ground to connection B11 on the Motronic control unit when P or N is engaged.
• ◆ When a gear is engaged the switch is open and a positive voltage is applied at connection B11 of the control unit.

Procedure:

• ‒ Connect the fault reader V.A.G 1551 => Page 01-4.
• ‒ Switch ignition on.
• ‒ Select "Read measured value block" (function 08) and Display group 20.

Specified value for Display zone 2: "Neutral" (selector lever in P or N)

• ‒ Depress the brake pedal and engage a gear.

Specified value: "Gear ENG"

• ‒ If the display is not as described, connect test box V.A.G 1598/19 to the wiring harness for Motronic control unit -J220 => Page 01-122.
• ‒ Connect a diode test lamp between socket D9 (permanent positive, terminal 30) and B11.
• ‒ The diode test lamp should go out when a gear is engaged.

• ‒ If the diode test lamp goes out even though the display in the measured value block was not OK, check the signal for the selector lever lock.

=> Automatic gearbox 01V; Repair Group 01; Gearbox Electrical testing

• ‒ → If the diode test lamp is permanently lit up or not lit up at all, check the wiring between contact B11 on the Motronic control unit and the multifunction switch according to the current flow diagram for short to positive or ground and for open circuit.
• ‒ If there is no fault in the wiring, check the multifunction switch

=> Automatic gearbox 01V; Repair Group 01; Gearbox: Electrical testing

Engine speed signal

Notes:

• ◆ The engine speed signal is sent to connection C10 of the Motronic control unit. The signal is used (among others) for the control unit of the automatic gearbox for calculation of the gearshift timing and for the speedometer display in the dash panel insert.

Procedure:

• ‒ → Connect test box V.A.G 1598/19 to the wiring harness of the Motronic control unit -J220 .
• ‒ Test for open circuit in wiring between dash panel insert and contact C10 using the current flow diagram.

Throttle valve position

Notes:

• ◆ This signal is used by the control unit of the automatic gearbox in conjunction with the engine speed to calculate the gearshift timing.
• ◆ This signal is a pulse-width modulated square-wave signal (duty cycle), which is output by the Motronic control unit at contact B1.

Procedure:

• ‒ Connect V.A.G 1551 .
• ‒ Start self-diagnosis on gearbox control unit.

=> Automatic gearbox 01V; Repair group 01; Self-diagnosis

• ‒ If fault 00638 "Engine/gearbox electrical connection 2" is displayed by the gearbox control unit, read out fault memory of Motronic control unit => Page 01-4.

• ‒ If the Motronic control unit has recorded a fault relating to the throttle valve potentiometer, rectify this fault first. (In this case the fault in the gearbox is a result of the fault in the potentiometer).

• ‒ → If no fault is displayed relating to the throttle valve potentiometer, connect test box V.A.G 1598/19 to the wiring harness for the Motronic control unit => Page 01-122.
• ‒ Test for open or short circuit in wiring between contact B1 and gearbox control unit using the current flow diagram.

Fuel consumption signal for trip computer

Note:

• ◆ The fuel consumption signal for the trip computer is output to connection C12 of the Motronic control unit.

Procedure:

• ‒ Observe operation of the on-board computer when the engine is running (instantaneous consumption).
• ‒ → If no readout at all appears: Stop engine. Remove Motronic control unit and connect V.A.G 1598/19 to wiring harness for Motronic control unit. Check for open circuit or short in wiring between contact C12 and connection 1 (multiplug connection, black 20-pin, on dash panel insert) using hand-held multimeter V.A.G 1526 according to the current flow diagram .

Vehicle speed signal

Notes:

• ◆ The vehicle speed signal is generated by the road speed sender -G68 (on the gearbox) and is processed in instrument cluster (dash panel insert).
• ◆ The processed signal goes to contact C13 on the Motronic control unit and is used for idling speed stabilisation and for the damping of load change jolts when changing gear on the automatic gearbox.
• ◆ The idling speed stabilisation is activated below 15 km/h and with the idling switch closed.

Procedure:

• ‒ Connect V.A.G 1551 and start the dash panel insert self-diagnosis

=> Electrical System; Repair Group 01; Self-diagnosis

• ‒ Select "Read measured value block" (function 08) and Display group 01.

• ‒ Take vehicle for a test drive and check whether the vehicle speed appears in Display zone 1.
• ‒ If the vehicle speed is not displayed, raise vehicle at front left until the wheel is clear of the ground.

• ‒ → Connect test box V.A.G 1598/19 to the wiring harness of the Motronic control unit .
• ‒ Connect the diode test lamp between socket D9 (positive) and C13 (signal).
• ‒ Switch on ignition and rotate front left wheel by hand.
• ‒ The diode test lamp should flash (very brief flashes).

Note:

• ◆ If necessary, hold the front right wheel to prevent it from turning.

• ‒ If the diode lamp does not flash, check for open circuit or short circuit in the wiring between connection C13 on the connector for the Motronic control unit and the dash panel insert according to the current flow diagram.

Ignition angle retardation during gearshifts

Note:

• ◆ Due to this signal from the gearbox control unit, the ignition angle is briefly retarded (torque reduction) by varying amounts depending on the vehicle speed and engine speed during gearshifts on the automatic gearbox, in order to reduce juddering gear changes.
• ◆ The signal is a square-wave signal which is received at connection B9 on the Motronic control unit.
• ◆ As the signal is very short, the ignition timing retardation demand from V.A.G 1551 (Display zone 3) is not always detected.

Procedure:

• ‒ Connect the fault reader V.A.G 1551 => Page 01-4.
• ‒ Perform a road test and read measured value block (function 08) and select Display group 19 .

• ‒ Display zone 3 shows the ignition timing retardation demanded by the automatic gearbox for the gearshift (specified value).
• ‒ Display zone 4 shows the effective ignition timing (actual value). This value cannot however be used for evaluation, as it constantly changes according to the engine speed and load.

• ‒ The wiring to the gearbox control unit is monitored by the self-diagnosis system (fault 00545) => Page 01-8.
• ‒ → If during a gearshift there is no display in the measured value block for the torque reduction, or if fault 00545 is displayed, connect test box V.A.G 1598/19 to the wiring harness for the Motronic control unit .
• ‒ Check for open circuit or short in the wiring between connection B9 of the Motronic control unit and connection 13 of the gearbox control unit according to the current flow diagram.