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Discovery 2. Manual - part 77

ENGINE MANAGEMENT SYSTEM - V8

DESCRIPTION AND OPERATION 18-2-37

There are eight IACV diagnostic checks performed by the ECM:

Output short circuit to earth – opening coil

Output short circuit to battery supply – opening coil

Output open circuit – opening coil

Output short circuit to earth – closing coil

Output short circuit to battery voltage – closing coil

Output open circuit – closing coil

Blocked IACV – rev/min error low (engine speed must be 100 rev/min less than the target speed, engine load
less than 2.5 and the measured air flow more than 10 kg/h less than the expected air flow for a fault condition to
be flagged).

Blocked IACV – rev/min error high (the engine speed must be more than 180 rev/min greater than the target
speed and the measured air flow more than 10 kg/h greater than the expected air flow for a fault condition to be
flagged).

Should a malfunction of the component occur, the following fault codes may be evident and can be retrieved by
TestBook.

P Code

J2012 Description

Land Rover Description

P1510

IACV opening coil malfunction

Short circuit to battery supply - opening winding

P1513

IACV opening coil malfunction

Short circuit to earth - opening winding

P1514

IACV opening coil malfunction

Open circuit - opening winding

P1553

IACV closing coil malfunction

Short circuit to battery supply - closing winding

P1552

IACV closing coil malfunction

Short circuit to earth - closing winding

P1551

IACV closing coil malfunction

Open circuit - closing winding

P0505

Idle control system malfunction

Blocked IACV - high or low rev/min error

ENGINE MANAGEMENT SYSTEM - V8

18-2-38 DESCRIPTION AND OPERATION

Fuel pump relay

The fuel pump relay is located in the engine compartment fuse box. It is a 4 pin normally open relay. Input from the
ECM allows the fuel pump relay to control the electrical input to the fuel pump, regulating the fuel supply to the fuel
injectors. When the ignition is switched on and the engine is cranked, the fuel pump relay is activated by the ECM,
allowing the fuel system to be pressurised to 3.5 bar (52 lbf.in

). The ECM then deactivates the relay until the engine

has started.

If the fuel pump runs, but the fuel pressure is out of limits, adaptive fuel faults will be stored.

Input/Output
The input value for the relay windings is battery voltage, the input value for the switching contacts comes from fuse
10 in the engine compartment fuse box. The output control of the switching contacts is direct to the fuel pump motor,
and the relay windings are controlled by pin number 18 of connector C0635 of the ECM.

At ignition 'on' (position II) the fuel pump relay contacts remain open until the ECM supplies an earth path for the relay
windings via pin number 18 of connector C0635 of the ECM. At this point, the relay windings are energised, drawing
the relay contacts closed. This allows voltage from fuse 10 in the passenger compartment fuse box to pass directly
to the fuel pump.

The fuel pump relay can fail the following ways or supply incorrect signal:

Relay drive open circuit.

Short circuit to vehicle earth.

Short circuit to vehicle supply.

Component failure.

In the event of a fuel pump relay failure any of the following symptoms may be observed:

Engine stalls or will not start.

No fuel pressure at the fuel injectors.

The ECM performs three types of diagnostic test to confirm the fuel pump relay integrity:

Output short circuit to earth

Output short circuit to battery voltage

Output open circuit

ENGINE MANAGEMENT SYSTEM - V8

DESCRIPTION AND OPERATION 18-2-39

Should a malfunction of the component occur the following fault codes may be evident and can be retrieved by
TestBook.

Evaporative emissions
Refer to Emissions section for description of the evaporative emissions system components.

EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Evaporative Emission Control System.

Secondary air injection (NAS only)
Refer to Emissions section for description of the secondary air injection system components.

EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Secondary Air Injection System.

Fuel tank pressure sensor (NAS only)
Refer to Fuel Delivery section for description of the fuel system components.

FUEL DELIVERY SYSTEM - V8, DESCRIPTION AND OPERATION, Description.

Refer to Emissions section for description of the fuel tank pressure sensor.

EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Evaporative Emission Control System.

P Code

J2012 Description

Land Rover Description

P1230

Fuel pump relay malfunction

Fuel pump relay open circuit - not the fuel pump

P1231

Fuel pump relay circuit low

Fuel pump relay short circuit to battery supply - not the
fuel pump

P1232

Fuel pump relay circuit high

Fuel pump relay short circuit to earth - not the fuel pump

ENGINE MANAGEMENT SYSTEM - V8

18-2-40 DESCRIPTION AND OPERATION

Ignition coils

Two double ended ignition coils are located at the rear of the engine, below the inlet plenum camber mounted on a
bracket. The ignition system operates on the wasted spark principle. When the ECM triggers an ignition coil to spark,
current from the coil travels to one spark plug jumping the gap at the spark plug electrodes igniting the mixture in the
cylinder. Current continues to travel along the earth path (via the cylinder head) to the spark plug negative electrode
at the cylinder that is on the exhaust stroke. The current jumps across the spark plug electrodes and back to the coil
completing the circuit. Since it has sparked simultaneously in a cylinder that is on the exhaust stroke it has not done
any work, therefore it is wasted.

The coils are paired in the following cylinder order:

1 and 6.

8 and 5.

4 and 7.

3 and 2.

The ECM calculates the dwell timing from battery voltage, and engine speed to ensure constant secondary energy.
This ensures sufficient spark energy is always available without excessive primary current flow and thus avoiding
overheating or damage to the coils. Individual cylinder spark timing is calculated from the following signals:

Engine speed.

Engine load.

Engine temperature.

Knock control.

Automatic gearbox shift control.

Idle speed control.

During engine warm up ignition timing should be an expected value of 12

BTDC.

TestBook can not directly carry out diagnostics on the high-tension side of the ignition system. Ignition related faults
are monitored indirectly by the misfire detection system.

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