Discovery 2. Manual — part 468

ENGINE MANAGEMENT SYSTEM - TD5

DESCRIPTION AND OPERATION 18-1-15

The ECT sensor can fail the following ways or supply incorrect signal:

l

Sensor open circuit.

l

Short circuit to vehicle supply.

l

Short circuit to earth.

l

Incorrect mechanical fitting.

l

Signal fixed above 40

°

C (104

°

F) not detected.

l

Signal fixed below 40

°

C (104

°

F) not detected.

In the event of an ECT sensor signal failure any of the following symptoms may be observed:

l

Difficult cold start.

l

Difficult hot start.

l

Driveability concerns.

l

Instrument pack temperature warning illuminated.

l

Temperature gauge reads excessively hot.

l

Temperature gauge reads excessively cold.

In the event of component failure the ECM calculates coolant temperature from the fuel temperature sensor signal. If
this occurs, the limit engine operation if coolant temperature is too high becomes inoperative.

The MIL will not illuminate in an ECT sensor failure.

ENGINE MANAGEMENT SYSTEM - TD5

18-1-16 DESCRIPTION AND OPERATION

Crankshaft speed and Position (CKP) sensor

The CKP is located in the transmission housing with its tip adjacent to the outer circumference of the flywheel. The
CKP sensor works on the variable reluctance principle, which sends a signal back to the ECM in the form of an ac
voltage.

The ECM uses the signal from the CKP for the following functions:

l

To calculate engine speed.

l

To determine engine crank position.

l

To determine fuel injection timing.

The CKP sensor works as a Variable Reluctance Sensor (VRS). It uses an electromagnet and a target ring to generate
a signal. As the target ring passes the tip of the CKP sensor the magnetic field produced by the sensor is cut and then
re-instated. The ECM measures the signal as an ac voltage.

The outer circumference of the flywheel acts as the target ring for the sensor. The flywheel is divided into 36 segments
each of 10

°

. 31 segments have drilled holes and 5 segments are spaces. This equals 360

°

or one engine revolution.

The 5 spaces correspond to the TDC position of the 5 cylinders, this allows the ECM to control fuel injection timing
for each of the cylinders.

Input/Output
The two pins on the sensor are both outputs. The ECM processes the outputs of the sensor. To protect the integrity
of the CKP signal an earth shield or screen is used.

The ECM measures the outputs from the CKP. The ECM measures the positive signal from the CKP at pin 13 of ECM
connector C0158. The ECM measures the negative signal from the CKP at pin 36 of ECM connector C0158. The earth
path is via pin 16 of ECM connector C0158.

Voltage generation from the CKP sensor is relative to engine speed. The values expected from a good CKP sensor
are as follows:

l

2 to 3 volts with engine cranking.

l

Rising to 6 to 6.5 volts from 1000 rev/min upwards.

The above readings are dependent upon correct air gap between the tip of the CKP sensor and the passing teeth of
the reluctor ring.

ENGINE MANAGEMENT SYSTEM - TD5

DESCRIPTION AND OPERATION 18-1-17

The CKP sensor can fail the following ways or supply incorrect signal:

l

Sensor assembly loose.

l

Incorrect spacer fitted.

l

Sensor open circuit.

l

Sensor short circuit.

l

Incorrect fitting and integrity of the sensor.

l

Water ingress.

In the event of a CKP sensor signal failure any of the following symptoms may be observed:

l

Engine cranks but fails to start.

l

MIL remains on at all times.

l

Engine misfires (CKP sensor incorrectly fitted).

l

Engine runs roughly or even stalls (CKP sensor incorrectly fitted).

CKP does not have any backup strategy and if it fails the engine will stop running and fail to start.

ENGINE MANAGEMENT SYSTEM - TD5

18-1-18 DESCRIPTION AND OPERATION

Throttle Position (TP) sensor – Up to VIN 297136

The TP sensor is located on the throttle pedal assembly. It detects throttle pedal movement and position. It uses two
position sensors to provide the ECM with the exact throttle pedal position. As the pedal operates the voltage of one
position sensor increases as the other decreases.

Input/Output
The ECM provides the throttle position sensor with a 5 volt reference feed. Both position sensors send an analogue
signal back to the ECM.

l

Sensor one, 0 to 5 volts variable.

l

Sensor two, 5 to 0 volts variable.

Input to the throttle pedal position sensor is via pin 14 of the ECM connector C0658. Output from sensor one is
measured via pin 12 of the ECM connector C0658. Output from sensor two is measured via pin 36 of the ECM
connector C0658. The earth path is via pin 26 of ECM connector C0658.

The TP sensor can fail the following ways or supply incorrect signal:

l

Sensor open circuit.

l

Short circuit to vehicle supply.

l

Short circuit to vehicle earth.

l

Water ingress.

l

Sensor incorrectly fitted.

In the event of a TP sensor signal failure any of the following symptoms may be observed:

l

Engine performance concern.

l

Delayed throttle response.

l

Failure of emission control.

If the TP sensor fails, the engine will only run at idle and the MIL will remain on until the fault is eliminated. Turning
the ignition off/on can reset the MIL provided that the fault has been rectified.