Another segment from my Smog License Class
ASE Certification Online – Scan Tool Data: Knock Sensor
The Scan Tool Data input, knock sensor is located in or near the engine block. The sensor detects abnormal vibration in the engine. This sensor produces a AC signal on a DC line. As the vibration or knock increases the knock sensor signal, ‘voltage” also increases.
Scan Tool Data:
This signal is sent to the PCM and base off this signal the PCM will retard the timing by controlling the ignition control module.
Pre 1998 knock sensor generated a AC signal on a DC line, it generates a voltage proportional to a ping or knock.
When plugged in the 5 volts is pulled down to 2.4 – 2.5 volts. When the PCM sees 2.4 – 2.5v it knows the circuit is good.
Scan Tool Data:
The knock sensor after 1998 does not have 5 volts to the sensor.
When the PCM detects a knock it will retard the timing in 2 degree increments until no knock is detected.
Other causes of a detonation and high emissions are:
- Loss of EGR
- Lean condition
- Over advance timing
- Excessive high engine temperature
- Combustion chamber carbon build up
Scan Tool Data……….
The spark control system uses the signal from the PCM, “Power Train Control Module” to control ignition timing.
In order to do this the PCM takes into consideration:
- Spark Knock Sensor
- Intake air temperature
- Engine Speed
- Engine Load
- Crank Position
- Engine Coolant temperature
The Exhaust Gas Recirculation (EGR) system is used to reduce to lower Oxides of Nitrogen (Nox) emissions levels caused by combustion temperatures.
It works by introducing a small amount of inert gases into the combustion chamber, which takes up space form air entering the combustion chamber. This will lower the combustion chambers temperature and lower Nox.
The EGR monitor uses several different components to check the circuit; one of the components is the MAP sensor. The monitor watches changes in the MAP sensor signal voltage, during EGR valve actuation, to determine how well the EGR is working. The EGR monitor will open the EGR valve during deceleration, close throttle or force it close during steady cruise operation.
If the EGR is open by the monitor, a change in manifold pressure will result. Also if the EGR is open during deceleration test, the manifold pressure will increase.
If the EGR valve is closed during cruise monitoring, the manifold pressure will decrease. The amount of MAP sensor change can be correlated to the amount of EGR flow.
A failure with the EGR monitor will result when the voltage change is incorrect based off preprogram information.
The PCM sends 5 volts to the MAP sensor as a reference voltage, the PCM also provides a ground and it watches the signal wire for pressure changes.
When the vacuum or pressure changes in the intake manifold, the Map sensor senses this change. A vacuum hose connect to the intake manifold to the MAP Sensor.
The PCM senses this change from the MAP sensor signal wire to determine the manifold pressure.
A lower pressure, (high vacuum) is indicated by a lower MAP sensor signal voltage, (.8volts – 1.0volts).
A higher pressure, (low vacuum) is indicated by a higher MAP sensor signal voltage, (3.8volts – 4.5volts)
Scantool Reading …………………
The higher the voltage reading the heavier the load more fuel is needed, the PCM will increase the pulse width.
Ex. A plugged Catalytic Converter will increase MAP sensor Voltage and cause a rich condition.
Map Sensor Conversion Chart
Scan Tool Data:
Example of a MAP Sensor Conversion Chart for KOEO Readings:
Metric Pressure (kPa)
100 9 0 80 70 60 50 40 30 20 10 0
English Pressure (Hg)
30 27 24 21 18 15 12 09 06 03 0
Voltage (V) from the MAP Sensor
4.8 4.4 3.8 3.3 2.7 2.2 1.7 1.1 0.6 0.3 0
Be patient the video will load depending on your computer speed
The internet is a great source of repair information. Using the internet is a great source of Technical Service Bulletins, (TSB) – Dealership Updates and repairs and Recalls.
Scan Tool Data…………..
The EVAP system is used to collect fuel vapor from the fuel tank. The vapors are stored in a canister and the canister is filled with carbon.
The EVAP system will store the vapors from the gas tank, and they are drawn from the canister and directed to the intake manifold to be burn in the combustion process.
OBD II requires PCM monitoring for proper operation of the EVAP system and for possible leaks to the atmosphere.
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