Diagnostics and testing 4.0L (Discovery 3)

Inspection and verification

1. Check the validity of the customer's complaint.

2. Visually inspect for obvious mechanical and electrical problems.

Mechanical factors	Electrical factors
Engine oil level Coolant level of the cooling system Fuel level Fuel contamination/fuel brand/fuel quality Installation/sensor status Fan with viscous coupling and electromagnetic valve	Fuses Wiring harness Electrical connector(s) Sensor(s) Engine Control Module (ECM) Transmission Control Module (TCM)

3. If an obvious cause for the problem you identified or the customer described is found, resolve it before proceeding with further actions. (if possible).

4. Using the approved diagnostic system or suitable scan tool, read all diagnostic trouble codes (DTCs) before proceeding to the Symptom Chart or DTC Index.

Clear all DTCs after troubleshooting.

Table of signs of malfunction

Sign (general)	Sign (characteristic)	Possible reasons	Action
No launch	The engine crankshaft does not turn	Security system/immobilizer activated ECM relay Battery Launch system Wiring harness Engine seizure	Make sure the security system is disabled. Check the operation of the ECM relay. Check the battery condition and charge. For information on starting system tests, refer to the appropriate section in the service manual. Check if the engine cranks manually.
No launch	The engine crankshaft turns, but no sparks occur.	Low fuel level/contamination Ignition system Fuel system Crankshaft Position Sensor (CKP) Wiring harness ECM failure	Check the fuel level and condition. For ignition and fuel system tests, refer to the appropriate section in the service manual. For CKP sensor and wiring harness tests, refer to the guided diagnostic routine on the approved diagnostic system. If ECM malfunction is suspected, refer to the warranty policy and procedures manual.
No launch	The engine crankshaft turns, flashes occur, but the engine does not start	Fuel Evaporative Emission Control System Canister Purge Valve Fuel system Spark plugs Ignition coil fault(s) Wiring harness	For information on checking the purge valve, fuel system, and ignition system, refer to the appropriate section in the service manual.
Difficult start	Difficulty starting at cold start	Check the antifreeze content in the coolant Battery Crankshaft Position Sensor (CKP) Fuel system Fuel Evaporative Emission Control System Canister Purge Valve	Check the coolant condition. Check the battery condition and charge. For CKP sensor tests, refer to the guided diagnostic routine on the approved diagnostic system. For fuel system and purge valve tests, refer to the appropriate section in the workshop manual.
Difficult start	Difficulty with hot start	Leak in the injector Fuel system Fuel temperature sensor Intake Air Temperature (IAT) Sensor Mass Air Flow (MAF) Sensor Fuel Evaporative Emission Control System Canister Purge Valve Ignition system	For injector and fuel system, fuel temperature sensor, IAT sensor, and MAF sensor tests, refer to the guided diagnostic routine on the approved diagnostic system. For purge valve and ignition system tests, refer to the appropriate section in the service manual.
Difficult start	Difficulty starting after hot soak (the car remains stationary for some time after the engine has reached operating temperature)	Leak in the injector Fuel system Fuel temperature sensor IAT sensor MAF sensor Fuel Evaporative Emission Control System Canister Purge Valve Ignition system	For injector and fuel system, fuel temperature sensor, IAT sensor, and MAF sensor tests, refer to the guided diagnostic routine on the approved diagnostic system. For purge valve and ignition system tests, refer to the appropriate section in the service manual.
Difficult start	The engine crankshaft turns too fast/slowly	High/low compression Battery Launch system	Check the compression. Check the battery condition and charge. For information on starting system checks, refer to the relevant section in the service manual.
The engine stalls	Engine stalls shortly after starting	Disconnection/reduction of ventilation system capacity ECM relay MAF sensor Ignition system Clogged air filter Air leak Fuel lines Fuel Rail Pressure (FRP) Sensor	Check the engine ventilation system. Check the operation of the ECM relay. For MAF sensor tests, refer to the guided diagnostic routine on the approved diagnostic system. For ignition system tests, refer to the appropriate section in the workshop manual. For air intake system and fuel line information, refer to the appropriate section in the workshop manual. For FRP sensor tests, refer to the guided diagnostic routine on the approved diagnostic system.
The engine stalls	Engine stalls when engine braking	ECM relay Throttle Position (TP) Sensors	Check the operation of the ECM relay. For throttle position sensor tests, refer to the guided diagnostic routine on the approved diagnostic system.
The engine stalls	The engine stalls at a steady speed	ECM relay CKP sensor Throttle Position Sensors	Check the operation of the ECM relay. For CKP sensor and TP sensor tests, refer to the guided diagnostic routine on the approved diagnostic system.
The engine stalls	Engine stalls when cruise control is on	ECM relay	Check the operation of the ECM relay.
The engine stalls	The engine stalls when maneuvering	ECM relay Throttle Position Sensors Additional engine loads (PAS, air conditioning, etc.) Gearbox failure CAN malfunction	Check the operation of the ECM relay. For throttle position sensor tests, refer to the guided diagnostic routine on the approved diagnostic system. For accessory drive and transmission information, refer to the appropriate section in the workshop manual. Check for CAN fault codes.
Poor handling	Engine hesitation on acceleration/poor acceleration	Fuel lines Leak in the injector Fuel pressure Air leak Throttle Position Sensors Throttle body motor Ignition system HO2 sensors Gearbox failure Difficulty moving the pedal (floor covering, etc.) Accelerator pedal position sensor (throttle position)	For information on checking the fuel pump, fuel lines, and air intake system, refer to the corresponding section in the Service station manual. To check the throttle position sensor and the throttle motor, refer to the directional diagnostic program in an approved diagnostic system. Ignition system checks are described in the relevant section of the service station manual. Check for DTC codes for HO2 sensors, refer to the DTC Code Index. For more information about the gearbox, refer to the corresponding section in the service station manual. Check the accelerator pedal movement. For throttle position sensor checks, refer to the directional diagnostic program in an approved diagnostic system.
Poor handling	Backfires in the engine	Fuel pump Fuel lines Air leak MAF sensor HO2 sensors Ignition system Throttle position sensor	For fuel pump, fuel lines, and air intake system information, refer to the appropriate section in the service manual. For MAF sensor tests, refer to the guided diagnostic routine on the approved diagnostic system. For HO2 sensor DTCs, refer to the DTC Index. For ignition system tests, refer to the appropriate section in the service manual. For throttle position sensor tests, refer to the guided diagnostic routine on the approved diagnostic system.
Poor handling	Engine jerks	Fuel pump Fuel lines MAF sensor Wiring harness Throttle Position Sensors Throttle body motor Ignition system	For fuel pump and fuel lines, refer to the appropriate section in the service manual. For MAF sensor, throttle position sensor, and throttle motor tests, refer to the guided diagnostic routine on the approved diagnostic system. Ignition system tests are described in the appropriate section of the service manual.
Poor handling	Detonation/knocking in the engine	Knock sensor (KS)/electrical circuit malfunction Fuel pump Fuel lines Fuel quality FRP sensor MAF sensor HO2 sensors Air leak BARO sensor malfunction (internal ECM failure)	To check the electrical circuits of the knock sensor, refer to the directional diagnostic program in an approved diagnostic system. For information about the fuel pump and fuel lines, refer to the corresponding section in the Service station manual. To check the FRP sensor and MAF sensor, refer to the directional diagnostic program in an approved diagnostic system. Check for DTC codes for HO2 sensors, refer to the DTC Code Index. For information about the air intake system, refer to the corresponding section in the Service station manual. If an ECM malfunction is suspected, refer to the warranty policy and procedures manual.
Poor handling	Lack of throttle response	Throttle position sensor malfunction Throttle Position Sensors Throttle body motor	For throttle position sensor and throttle motor tests, refer to the guided diagnostic routine on the approved diagnostic system.
Poor handling	Disabling or disabling the cruise control system	Default mode is enabled Cruise control switch(es) Throttle Position Sensors CAN Bus Malfunction	Check the message center for a default message. For cruise control switches, refer to the relevant section in the workshop manual. For throttle position sensor tests, refer to the guided diagnostic routine on the approved diagnostic system. Check for CAN fault codes.
Poor handling	Poor throttle response	Throttle position sensor malfunction Throttle Position Sensors ECT sensor MAF sensor Gearbox failure Activating the traction control system Air leak Disconnection/reduction of ventilation system capacity	For throttle position sensor, eCt sensor, and MAF sensor tests, refer to the guided diagnostic routine on the approved diagnostic system. For transmission, air intake system, and ventilation system information, refer to the appropriate section in the workshop manual.
Poor handling	The engine management system has gone to default values, indicator lamp and messages. Refer to the owner's manual.	Throttle Position Sensors MAF sensor ECT sensor Wiring harness	For throttle position sensor, MAF sensor, and ECT sensor tests, refer to the guided diagnostic routine on the approved diagnostic system.