Discovery 2. Manual - part 62

 

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Discovery 2. Manual - part 62

 

 

EMISSION CONTROL - V8

DESCRIPTION AND OPERATION 17-2-43

Secondary Air Injection System 
Operation

When the engine is started, the engine control module checks the engine coolant temperature and if it is below 55

°

 

C, the ECM grounds the electrical connection to the coil of the secondary air injection (SAI) pump relay.

A 12V battery supply is fed to the inertia switch via fuse 13 in the engine compartment fusebox. When the inertia 
switch contacts are closed, the feed passes through the switch and is connected to the coil of the Main relay. An earth 
connection from the Main relay coil is connected to the ECM. When the ECM completes the earth path, the coil 
energises and closes the contacts of the Main relay. 

The Main and Secondary Air Injection (SAI) pump relays are located in the engine compartment fusebox. When the 
contacts of the Main relay are closed, a 12V battery supply is fed to the coil of the SAI pump relay. An earth connection 
from the coil of the SAI pump relay is connected to the ECM. When the ECM completes the earth path, the coil 
energises and closes the contacts of the SAI pump relay to supply 12V to the SAI pump via fusible link 2 in the engine 
compartment fusebox. The SAI pump starts to operate, and will continue to do so until the ECM switches off the earth 
connection to the coil of the SAI pump relay. 

The SAI pump remains operational for a period determined by the ECM and depends on the starting temperature of 
the engine, or for a maximum operation period determined by the ECM if the target engine coolant temperature has 
not been reached in the usual time.

When the contacts of the main relay are closed, a 12V battery supply is fed to the SAI solenoid valve via Fuse 2 in 
the engine compartment fusebox.

The ECM grounds the electrical connection to the SAI vacuum solenoid valve at the same time as it switches on the 
SAI pump motor. When the SAI vacuum solenoid valve is energised, a vacuum is provided to the operation control 
ports on both of the vacuum operated SAI control valves at the exhaust manifolds. The control vacuum is sourced 
from the intake manifold depression and routed to the SAI control valves via a vacuum reservoir and the SAI vacuum 
solenoid valve.

The vacuum reservoir is included in the vacuum supply circuit to prevent vacuum fluctuations caused by changes in 
the intake manifold depression affecting the operation of the SAI control valves.

When a vacuum is applied to the control ports of the SAI control valves, the valves open to allow pressurised air from 
the SAI pump to pass through to the exhaust ports in the cylinder heads for combustion.

When the ECM has determined that the SAI pump has operated for the desired duration, it switches off the earth paths 
to the SAI pump relay and the SAI vacuum solenoid valve. With the SAI vacuum solenoid valve de-energised, the 
valve closes, cutting off the vacuum supply to the SAI control valves. The SAI control valves close immediately and 
completely to prevent any further pressurised air from the SAI pump entering the exhaust manifolds.

The engine coolant temperature sensor incurs a time lag in respect of detecting a change in temperature and the SAI 
pump automatically enters a 'soak period' between operations to prevent the SAI pump overheating. The ECM also 
compares the switch off and start up temperatures, to determine whether it is necessary to operate the SAI pump. 
This prevents the pump running repeatedly and overheating on repeat starts.

Other factors which may prevent or stop SAI pump operation include the prevailing engine speed / load conditions.

EMISSION CONTROL - V8

17-2-44 DESCRIPTION AND OPERATION

SAI System Fault Finding and Check 
Malfunctions

The SAI system diagnostics monitor the whole SAI system for correct operation. Malfunction of any one of the SAI 
system components can cause fault codes to be stored in the ECM diagnostic memory.

Correct fault finding methods and investigation are essential to determine the root cause of the generated fault code(s) 
and prevent mis-diagnosis.

NOTE: TestBook/T4 must be used to perform active SAI diagnostics.

Fault Finding
In the event of SAI system malfunction and P Codes 1412 – 1417 being stored in the ECM diagnostic memory, the 
following information is designed to provide a logical checking process for investigation of the root cause(s) of the 
fault. This fault finding guide should be used in conjunction with the following 'Checking Malfunctions' procedure and 
other information contained in this Emissions section.

It is important that these procedures are performed to prevent the following:

l

Excessive instances of No Fault Found (NFF) components in warranty returns

l

Multiple repeat complaints from the customer before the cause of the fault is found.

The following table lists the P codes applicable to the SAI system and their meaning:

Passive Test (P Codes 1412 and 1415)

During normal SAI operation the ECM uses HO2S sensor voltage output to determine if sufficient flow is being 
introduced into the exhaust system. Depending on which banks of the engine detect the fault, one or both P codes 
can be stored.

Active Tests

If the normal operation of the passive SAI diagnostics cannot be completed, (SAI operation being suspended by load/
speed conditions, for instance) the ECM will attempt to perform an 'Active' test of the system when conditions allow. 
These conditions include, but are not limited to: 'Engine fully warm' and 'Engine at idle'. The active test comprises two 
parts; a 'Leak Test' followed by a 'Flow Test'.

Leak Test (P Codes P1413 and P1416)
The SAI pump is operated without opening the SAI control valves. In this condition no SAI flow should enter the 
exhaust system. By monitoring the HO2S sensor voltage output, the ECM determines if the system is functioning 
correctly. Depending on which bank of the engine detects the fault, one or both P codes can be stored.

P-code

Description

P1412

Secondary Air Injection System – Malfunction Bank 1 LH (Insufficient SAI flow 
during passive test)

P1413

Secondary Air Injection System – Air control valve always open Bank 1 LH 
(Excessive SAI flow during active leak test)

P1414

Secondary Air Injection System – Malfunction Bank 1 LH (Insufficient SAI flow 
during passive test)

P1415

Secondary Air Injection System – Malfunction Bank 2 RH (Insufficient SAI flow 
during passive test)

P1416

Secondary Air Injection System – Ait control valve always open Bank 2 RH 
(Excessive SAI flow during active leak test)

P1417

Secondary Air Injection System – Low air flow Bank 2 RH (Insufficient SAI flow 
during active test)

EMISSION CONTROL - V8

DESCRIPTION AND OPERATION 17-2-45

Flow Test (P Codes P1414 and P1417)
When the Leak test has been passed successfully, the SAI control valves are then opened while the SAI pump is still 
operational. Flow should now begin to enter the exhaust system. By monitoring the HO2S sensor voltage output, the 
ECM determines if sufficient flow is being introduced into the exhaust system. Depending on which bank of the engine 
detects the fault, one or both P codes can be stored.

Fault Finding Methodology
Malfunctions can be broadly categorised into two different categories: Flow Faults or Leak Faults.

Additionally, they also differ depending if the corresponding P code exists for both cylinder banks simultaneously or 
is unique to one bank, for example:

Faults of each of the four basic types should be investigated in a different priority order, starting with the most logically 
plausible cause or component.

Fault Finding Flow Charts
The following flow charts show the order of investigation that should be performed depending on the type of fault 
present. These should be treated as guidelines to ensure that the most likely and plausible causes are addressed first.

However, the flow charts assume that no clear or obvious reason for failure exists. If the cause of the malfunction is 
immediately obvious, then the flow charts should not be followed.

Once a malfunction is identified, it should be rectified as necessary and the system checked as per the instructions 
in the following 'Checking Malfunctions' section.

NOTE: It is not necessary to follow the remainder of the flow chart once a potential root cause has been identified.

Flow Fault Finding chart

Fault codes P1412, P1414, P1415 or P1417 present
Insufficient flow detected
Is fault present on both cylinder banks?

If 'NO'  proceed to step 4

If 'YES'  proceed to step 8

Vacuum supply – Check for: blockage and/or vacuum line disconnected from SAI valve
SAI Valve – Check for: jam / diaphragm leak or blockage
Delivery Hoses to SAI Valve – Check for: blockage / leaks
SAI Pipes to Cylinder Head – Check for: blockage / leaks
Electrical Issue – Check for: Related P code (relay/fuse/solenoid), rectify as necessary and check connectors
Vacuum Supply – Check for: Blocked/leaking vacuum lines or correct solenoid operation (open/closed)

10 Delivery Hoses – Check for: Blocked/leaking hoses
11 SAI Pump – Check for: Correct operation using TestBook/T4 or pump blockage/failure
12 SAI Valves – Check for: Both SAI Valves jammed/blocked/leaking diaphragms

Leak Fault Finding Chart

Fault codes P1413 or P1416 present
SAI system leak detected
Is fault present on both cylinder banks?

If 'NO'  proceed to step 4

If 'YES'  proceed to step 5

SAI Valve – Check for: leakage
Vacuum supply – Check for: solenoid stuck open (mechanical failure) or stuck open (electrical failure)
SAI Valve – Check for: leakage from one or both valves

P Code Type

One Bank Only

Both Banks

Flow

I

II

Leak

III

IV

EMISSION CONTROL - V8

17-2-46 DESCRIPTION AND OPERATION

Checking Malfunctions
In the event of faults in the Secondary Air Injection system such as noticeable noise, scorching on the lines or fault 
indication P Codes, all components and the system must be tested for proper functioning on completion of repairs.

Long term malfunctions with some components can result in damage to other system components. This can result in 
excessive instances of No Fault Found (NFF) components in warranty returns and multiple repeat complaints from 
the customer before the fault is rectified.

For example; a malfunction of the vacuum solenoid could result in uncontrolled opening of the SAI control valves. The 
could eventually lead to damage to the SAI valves and also the SAI pump. In this case, if only the pump was replaced, 
repeated failure may eventually occur over a period of time.

Necessary Tests

 

 

 

 

 

 

 

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