Engine Control Sensors - Removal and Installation: Diagnosis Volvo S80 I

Diagnostic Trouble Code (DTC)

The specific diagnostic trouble code (DTC) that has frozen values.

Frozen values dependent on diagnostic trouble codes (DTCs)

At the end there are some frozen values (normally four) which vary depending on the diagnostic trouble code (DTC) that is stored

Scheme 161

The engine control module (ECM) controls the camshaft reset valve (CVVT) steplessly. The pressure of the engine oil is used to regulate the CVVT unit.

The CVVT is installed on the intake camshaft on all B5244 engines.

There are 30 camshaft degrees (60 crankshaft degrees) between the limit positions.

The variable camshaft is hydraulically controlled by the engine oil. The camshaft turns when the camshaft reset valve (CVVT) releases lubricating oil into the front (A) or rear chamber (B) of the CVVT unit. The chambers are separated by a piston which is secured in the camshaft. The piston is secured in the cover of the CVVT unit by splines so that it moves easily. When the oil acts on the piston, the piston twists. The pulse wheel for the timing belt is on the outer cover of the CVVT unit.

Regulation is precise and rapid.

The camshaft reset valve (CVVT) has extremely fine ducts. This allows for precise regulation. However as a result the reset valve is sensitive to contaminants.

The main role of the variable camshaft is to reduce exhaust emissions, especially during cold starting. Idle quality is also improved.

Before the engine starts, there is an internal check consisting of the following stages

1. When the ignition is switched on, there is an electrical check of the signal cable, the power supply cable and the solenoid. This check checks for a short-circuit to supply voltage or ground and open-circuits
2. The camshaft is checked to ensure that it is in the correct position in relation to the flywheel, with the camshaft in its 0 position (mechanical resting position). This can be done by comparing the signals from the camshaft position (CMP) sensor and the engine speed (RPM) sensor. If there is too much deviation between these, the camshaft reset valve (CVVT) is not activated and a diagnostic trouble code (DTC) is stored
3. During greater control of the variable camshaft, the amount of time taken to deploy the camshaft to the desired value is measured. This time is used partly to assess how long it takes to change the angle of the camshaft and partly to disengage the variable camshaft if the time exceeds a certain maximum limit. The camshaft uses the engine oil and the oil pressure to turn itself. The rotation time varies, depending on factors such as engine speed (RPM), oil pressure and the viscosity of the oil (which depends open the temperature and quality of the oil)
4. The signal from the camshaft position (CMP) sensor is compared with the signal from the engine speed (RPM) sensor when the engine is turned over to ensure that it is correct. The check stops when the engine has started. If the check returns faulty values, a diagnostic trouble code (DTC) is stored and there is no camshaft control (CVVT).

Control

Scheme 162

Control takes place as follows when deploying the camshaft

1. Oil is forced from the engine lubricating system to the intake port on the reset valve
2. The engine control module (ECM) grounds the valve, the position of the piston in the valve changes and the oil is guided to the continuous variable valve timing (CVVT) unit chamber (A1) via the duct (A2) in the camshaft
3. The continuous variable valve timing (CVVT) unit hub is pressed backwards by the oil pressure. The continuous variable valve timing (CVVT) unit then rotates the hub and the carriers are joined by twisted splines
4. The oil flows to the engine sump via the outer ducts on the hub and the reset valve's return hose.

Control takes place as follows when returning the camshaft

1. Oil is forced from the engine lubricating system to the intake port on the reset valve
2. The engine control module (ECM) breaks the ground connection for the valve. The piston in the valve is then pressed back by a spring. The oil flows to the continuous variable valve timing (CVVT) unit chamber (B1) via a duct (B2) in the camshaft
3. The hub of the continuous variable valve timing (CVVT) unit is forced forward by the oil pressure that is created. The continuous variable valve timing (CVVT) unit will rotate back to the non-deployed position
4. The oil flows to the engine oil sump via the center duct on the hub and the reset valve's return duct.

The above takes place very quickly. The engine control module (ECM) controls the deployment and return of the reset valve continually at high frequency. This results in rapid and exact control.

There are diagnostics for this function.

Scheme 163

Knock occurs in the combustion chamber when the fuel and air mixture self ignites. This can occur either before or after the spark plug has produced an ignition spark. In both cases the gas in two or more places ignites in the combustion chamber.

This results in an extremely fast combustion process with flames from several directions. When these flames collide, the pressure in the cylinder increases rapidly and there is a mechanical knocking sound.

If any of the cylinders knock there is a specific type of vibration in the cylinder block. These vibrations are transferred to the knock sensors (KS) which are screwed into place in the cylinder block. The resultant mechanical stress in the piezo electrical material in the knock sensors generates a voltage. The engine control module (ECM) can then determine which cylinder is knocking with the help of the camshaft position (CMP) sensor and the engine speed (RPM) sensor.

The knock sensors (KS) also interpret a proportion of normal engine sound. The control module is able to recognize the vibrations which correspond to knocking by filtering, amplifying and using software to evaluate the signal.

If the knock sensors (KS) detect knocking in the engine above a certain threshold value, the ignition timing is first retarded and then the fuel / air mixture is enriched to eliminate knocking.

Scheme 164

The following components are used for ignition control

1. engine speed sensor (7/25)
2. camshaft position (CMP) sensor (7/172)
3. mass air flow (MAF) sensor (7/17)
4. engine coolant temperature (ECT) sensor (7/16)
5. electronic throttle module (ETM) (4/50)
6. knock sensor (KS) (7/23-7/24)
7. transmission control module (TCM) (4/28)
8. spark plugs with ignition coils (20/3-20/8)
9. brake control module (BCM)/anti-lock brake system module (ABS), (4/16).

The engine control module (ECM) calculates the optimum ignition advance based on the software and information from the sensors. The engine control module (ECM) cuts the current to the ignition coil mounted on the cylinder to be ignited and produces a spark.

During the starting phase the engine control module (ECM) produces a fixed ignition setting. When the engine starts and the car is driven the engine control module (ECM) calculates the optimum ignition setting according to the engine speed (RPM), load, temperature etc.

The engine control module (ECM) analyses the signal from the knock sensors (KS) when the engine reaches operating temperature. If any of the cylinders knock, the ignition is retarded for that specific cylinder until the knocking ceases.

The ignition then advanced to the normal position or until the knock recurs.

Before the gearbox control module (TCM) changes gear, it sometimes transmits a torque limiting request to the engine control module (ECM). The engine control module (ECM) then retards the ignition momentarily to reduce the torque, resulting in smoother gear changes and reducing the load on the gearbox. There are different ignition retardation levels depending on the signals from the gearbox control module (TCM). The return signal from the engine control module (ECM) to the gearbox control module (TCM) confirms that the signal reached the engine control module (ECM). The brake control module (BCM)/ABS control module transmits information to the engine control module (ECM) about deviations in the drive line. The signal is used to stop the diagnosis.

For further information, also see Misfire diagnostic .

The engine misfires if the fuel does not ignite correctly. See Misfire diagnostic .

Shutting off the misfire diagnostic

Misfire diagnostics are shut off in the event of

1. driveline oscillations. Drive line oscillations, caused by uneven road surfaces for example, may lead to uneven engine operation. Drive line oscillations will be posted by the ABS system and this information is sent to the engine control module (ECM). The engine control module (ECM) uses this information in order to differentiate between oscillations and actual misfiring and the diagnostic is shut off.
2. diagnostic trouble codes (DTCs) in the flywheel sensor, mass air flow (MAF) sensor, ABS and camshaft position (CMP) sensor.