Ford Focus Service Manual: Electronic Engine Controls

The electronic engine controls consist of the following:

• PCM
• Cylinder Head Temperature (CHT) sensor
• Camshaft Position (CMP) sensor
• Crankshaft Position (CKP) sensor
• Power Steering Pressure (PSP) switch
• Mass Air Flow (MAF) sensor
• Heated Oxygen Sensor (HO2S)
• Catalyst Monitor Sensor (CMS)
• Knock Sensor (KS)
• Swirl control valve sensor

The PCM:

• accepts input from various engine sensors to compute the fuel flow rate and spark timing necessary to maintain a prescribed air/fuel ratio throughout the entire engine operating range.
• outputs a command to the fuel injectors to meter the appropriate quantity of fuel.

The CHT sensor:

• sends the PCM a signal indicating cylinder head temperature.
• resistance decreases as coolant temperature increases.

The CMP sensor:

• provides camshaft position information which is used by the PCM for fuel synchronization.

The CKP sensor:

• sends the PCM a signal indicating crankshaft position.
• is essential for calculating spark timing.

The PSP switch:

• is a normally closed switch that opens as pressure increases.
• is used to send a signal to the PCM to adjust idle speed. This compensates for additional load on the engine from the power steering pump.

The MAF sensor:

• uses a hot wire sensing element to measure the amount of air entering the engine.
• uses a second hot wire to measure intake air temperature.
• sends signals to the PCM. The PCM will then calculate the required fuel injector pulse width in order to provide the desired air/fuel ratio.

The HO2S :

• has the ability to create a voltage signal dependent on exhaust oxygen content.
• provides feedback information to the PCM used to calculate fuel delivery.

The CMS :

• has the ability to create a voltage signal dependent on exhaust oxygen content.
• provides feedback information to the PCM used to calculate catalyst efficiency.

The KS :

• sends a signal to the PCM indicating engine detonation, which retards the ignition timing as necessary.

The swirl control valve sensor:

• monitors the position of the swirl control lever.