Volkswagen Golf / Golf GTI / Golf Variant. Manual - part 84

Qualification Explanation

Qualification

Area of Application

Hybrid electrically instructed

person

May perform general work and

Maintenance services on the

vehicle. May be requested by

the high voltage technician to

perform mechanical work on

the tension-free high voltage

system.

High voltage technician (HVT) The high voltage technician has

the same authorization as a

technician trained in electrical

systems due to their qualifica‐

tions. The high voltage techni‐

cian can also:

♦ 1. De-energize the system.
♦ 2. Secure the system so that

it cannot be energized

again.

♦ 3. Ascertain that the system

is definitely de-energized

(certified measurement).

♦ 4. Assign work on the high

voltage system to the hybrid

electrically instructed per‐

son.

♦ 5 Put the vehicle back in op‐

eration.

High voltage expert (HVE)

A high voltage expert (HVE) is

actually a high voltage techni‐

cian (HVT) but with an extra

qualification that allows them to

de-energize the high voltage

system in the case that a high

voltage technician is not able to

perform measurements with

the standard tools and equip‐

ment. The high voltage expert

must continue the work if the

high voltage technician does

not have the authority to work

on the high voltage system. The

high voltage expert is responsi‐

ble exclusively to de-energize

the high voltage system if it can‐

not be de-energized by the high

voltage technician using the

usual means or methods.

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1. General Information     

9

2

Description and Operation

♦

⇒ “2.1 On Board Diagnostic Systems”, page 10

♦

⇒ “2.2 Evaporative Emission System”, page 10

♦

⇒ “2.3 Electronic Throttle Control (ETC) System”, page 12

♦

⇒ “2.4 Electronic Power Control (EPC) Warning Lamp”,

page 12

♦

⇒ “2.5 Engine Control Module (ECM)”, page 13

♦

⇒ “2.6 Malfunction Indicator Lamp (MIL)”, page 13

♦

⇒ “2.7 Controller Area Network (CAN)”, page 13

♦

⇒ “2.8 Fuel Supply”, page 14

♦

⇒ “2.9 Ignition and Timing”, page 15

♦

⇒ “2.10 Variable Valve Timing”, page 16

♦

⇒ “2.11 Exhaust-Gas Recirculation (EGR) System”,

page 16

♦

⇒ “2.12 Secondary Air Injection”, page 16

♦

⇒ “2.13 Exhaust Systems”, page 16

2.1

On Board Diagnostic Systems

On Board Diagnostics, or OBD, is an automotive term referring to

a vehicle's self-diagnostic and reporting capability. OBD systems

give the vehicle owner or repair technician access to the status

of the various vehicle sub-systems. Modern OBD implementa‐

tions use a standardized digital communications port to provide

real-time data in addition to a standardized series of Diagnostic

Trouble Codes (DTCs) which allow one to rapidly identify and

remedy malfunctions within the vehicle. Legislation mandates a

vehicle equipped with OBD-II to light up the fault indicator lamp if

its emissions exceed the prevailing limit due to system malfunc‐

tion.
All cars built since January 1st, 1996 (MY 1996) are equipped

OBD-II systems. Manufacturers started incorporating OBD-II in

various models as early as 1994; however, some early OBD-II

cars (MY 1994 and MY 1995) were not 100% compliant.

2.2

Evaporative Emission System

The evaporative emission system has been designed to minimize

the release of hydrocarbons from the fuel system into the atmos‐

phere. The evaporative emission system components all work

together with the ECM to prevent fuel vapor from escaping and

route it to the intake manifold to be burned during normal com‐

bustion.
The leak detection system checks the integrity of the evaporative

emission system by pressurizing the system.
♦ There are 3 different types of evaporative emission systems

used. These systems are explained below.

♦

⇒ “2.2.1 Leak Detection Pump (LDP) Evap System”,

page 11

♦

⇒ “2.2.2 Tank Leak Diagnostic Module (DM - TL) Evap Sys‐

tem”, page 11

♦

⇒ “2.2.3 Natural Vacuum Leak Detection (NVLD) Evap Sys‐

tem”, page 11

♦

⇒ “2.2.4 EVAP System, Checking for Leaks”, page 11

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2.2.1

Leak Detection Pump (LDP) Evap Sys‐

tem

The leak detection pump (LDP) is integrated into the EVAP sys‐

tem and can have two functions. The LDP can:
♦ Pressurize the EVAP system and detect a drop in pressure

that would indicate a leak.

♦ Function as the EVAP Canister Vent on vehicles that do not

have a separate EVAP Canister Vent.

The LDP is a vacuum-driven, ECM controlled, diaphragm pump.

In order to operate, the engine must be running and vacuum ap‐

plied to the Vacuum Switch.

2.2.2

Tank Leak Diagnostic Module (DM - TL)

Evap System

The canister purge valve can be actively checked using the Tank

Leak Diagnostic Module (DM - TL). For this purpose the electric

pump is shortly activated while the combustion engine is running,

to build up a minor pressure in the fuel tank and monitor the pres‐

sure decay after opening the canister purge valve. Optionally as

a quick pass method, the monitoring can be carried out by pas‐

sively monitoring the fuel mixture deviation when the canister

purge valve is opened. If a significant fuel mixture deviation is

detected, the purge valve monitor passes. The Tank Leak Diag‐

nostic Module (DM - TL) consists of an electrically operated air

pump, an orifice with a defined diameter serving as a reference

leak, and a change-over valve switching the air flow between the

reference leak and the tank. If neither the pump nor the change-

over valve is activated, the tank is ventilated through a bypass in

the module.

2.2.3

Natural Vacuum Leak Detection (NVLD)

Evap System

The system utilizes an engine-off natural vacuum evaporative

system integrity check that tests for leaks with a diameter of 0.020

inch while the engine is off and the ignition is off. The natural vac‐

uum leak detection (NVLD) evaporative system integrity check

uses a pressure switch to detect evaporative system leaks. The

correlation between the pressure and the temperature in a sealed

system is used to generate a vacuum in the tank when the tem‐

perature drops. If a sufficient temperature drop is detected for a

minimum time period, the vacuum level in a sealed system will

exceed the threshold to close the NVLD pressure switch. There‐

fore, if the switch does not close under these conditions, a leak is

detected. If the switch closes, the system is considered to be leak-

free.

2.2.4

EVAP System, Checking for Leaks

The following procedure is used to diagnose EVAP System leaks.
Special tools and workshop equipment required
♦ Smoke tester.
♦ EVAP and Fuel Supply System Vacuum hose and line routing

diagram.

Leak checking
– Using a Smoke tester, check the Evaporative Emission

(EVAP) canister system for leaks.

– Always follow the manufacturers directions for the proper in‐

stallation and operation of the smoke tester being used.

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2. Description and Operation     

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If a leak is detected:
– Check the fuel filler cap seal for damage and for proper instal‐

lation. Replace if necessary.

– Check all hose connections of the fuel supply system and re‐

place or repair any leaking lines.

– Check all hose connections of the EVAP system and replace

or repair any leaking lines.

– Check that the seal under the locking flange is properly tight‐

ened on the fuel tank.

– Secure all hose connections using appropriate fittings for the

model type.

– Replace seals and gaskets when performing repair work.
– Repair or replace any damaged component.
If no leaks are found in the EVAP system:
– Erase the DTC memory if a DTC was set. Refer to

⇒ “3.3.4 Diagnostic Mode 04 - Erase DTC Memory”,

page 26

 .

– Perform a road test to verify repair.
If a DTC was set and does not return:
Diagnosis complete. Generate readiness code. Refer to

⇒ “3.2 Readiness Codes”, page 19

 .

If the same DTC does return and no leaks are found in the EVAP

system:
– Check for any related TSB's.
– Perform the diagnostic test procedure for the suspected com‐

ponent.

2.3

Electronic Throttle Control (ETC) Sys‐

tem

The electronic throttle control (ETC) system consists of the ac‐

celerator-pedal module, the engine control module (ECM), and

the electronic throttle body. The electronic throttle body mainly

consists of the throttle valve, the electric throttle-valve drive ele‐

ment, and the throttle-valve position sensor (TPS). The drive

element is a DC servomotor, which acts on the throttle-valve shaft

via a gear unit. The throttle-valve position sensor is a redundant

sensor system that detects the position of the throttle valve. The

sensors have opposite resistance curves so that the ECM can

always cross check the signals to ensure the correct position of

the throttle valve is always known.
The driver command is detected by a redundant sensor system

in the accelerator-pedal module, and the signal is sent to the en‐

gine control module. The engine control module then determines

the required throttle-valve position by performing calculations

from data measured by sensors such as accelerator pedal posi‐

tion sensor, engine speed sensor and vehicle speed sensor. The

actual throttle opening can be more or less in proportion to ac‐

celerator pedal position given different engine operating points.

2.4

Electronic Power Control (EPC) Warn‐

ing Lamp

When the ignition is switched on, the engine control module

(ECM) checks the electronic throttle control system for static sys‐

tem integrity (e.g. circuit integrity, communications, etc); the elec‐

tronic power control (EPC) warning light is turned on via the

Instrument Cluster during this process. Shortly after engine start,

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