Diagnostic functions
The EMS2000 fuel/ignition system control module has an on-board diagnostic (OBD) system for self-diagnosis, continuously monitoring input and output signals and several other functions.
If the engine control module (ECM) detects a fault, the value of eight different parameters are frozen and substitute values are activated to allow the system to continue operating. Diagnostic trouble code (DTC), type of fault and frozen values are stored in the engine control module (ECM) memory. If a fault disappears after the diagnostic trouble code (DTC) has been stored, information about the fault is stored in the engine control module (ECM). Every time the fault recurs a counter (CNT.ERR) counts it. For every warm-up cycle that is driven without the fault recurring a second counter (CNT.DEL) counts down. It begins with 40 and counts down to 0. A warm-up cycle means that engine coolant temperature (ECT) must reach at least 71°C and that engine coolant temperature (ECT) must rise by at least 22°C. When the second counter (CNT.DEL) has counted down to 0 the diagnostic trouble code (DTC) is erased from the engine control module (ECM) memory. If the fault recurs the second counter (CNT.DEL) is set to 40.
The on-board diagnostic (OBD) system also makes it possible to read off the value and status of a number of parameters. In addition a number of system components can be activated using the on-board diagnostic (OBD) system.
If the fuel/air mixture does not combust in any one cycle or does not burn as it should, the engine is said to be misfiring. The control module can detect misfiring by recording the time between two segments on the flywheel/carrier plate.
misfiring
flywheel mechanical tolerances
driveline oscillations
normal variations caused by uneven combustion
poor roads.
Since mechanical tolerances and drive train oscillation interfere with the signal, it is difficult to ascertain whether or not this interference is due to misfiring. To eliminate mechanical faults in the flywheel the flywheel signal is adapted. Two crankshaft revolutions are divided into four periods, if the engine is unloaded all four periods should be equal.
This is to even out the signal, so that a mechanical fault in the flywheel is not registered as misfiring.
After adaptation there is some interference in the signal due to oscillations in the drive train and normal engine irregularities.
engine speed is between 3,000 rpm and 3,600 rpm
the fuel shut-off system is operating and has been active for 100 revolutions.
Diagnostic trouble code (DTC) EFI-543 is stored for misfiring which leads to increased emissions and diagnostic trouble code (DTC) EFI-545 is stored for misfiring which could cause damage to the three-way catalytic converter (TWC).
The engine control module (ECM) registers and stores the engine speed and load range in which the misfiring occurred. The malfunction indicator lamp (MIL) lights if misfiring occurs again within the same engine speed and load range. If misfiring ceases, the engine must go through this entire engine speed and load range without a misfire before the engine control module (ECM) starts counting down to put out the malfunction indicator lamp (MIL) and erase the misfire codes.
Two heated oxygen sensors (HO2S) are used in the EMS2000 system. The heated oxygen sensors (HO2S) are checked as usual for short-circuits and open-circuits. If either of these faults occurs, diagnostic trouble code (DTC) EFI-212 (front heated oxygen sensor (HO2S)) or EFI-153 (rear heated oxygen sensor (HO2S)) are stored. In addition, the signal from the front heated oxygen sensor (HO2S) is checked. This check is carried out as follows: The engine control module (ECM) receives exhaust composition data from the front heated oxygen sensor (HO2S). Using this information the engine control module (ECM) calculates injection period. Because the front heated oxygen sensor (HO2S) is located upstream of the three-way catalytic converter (TWC) it is subject to attack by the uncleaned exhaust gases. This leads to the sensor aging and its signal changing
front heated oxygen sensor (HO2S) mean signal voltage
rear heated oxygen sensor (HO2S) control
front heated oxygen sensor (HO2S) period.
To determine front heated oxygen sensor (HO2S) mean voltage the engine control module (ECM) uses the rear heated oxygen sensor (HO2S) signal. This signal provides information about the exhaust gas oxygen composition downstream of the catalytic converter. The engine control module (ECM) can use this information to take account of front sensor aging in its injection period computations.
The mean rear sensor signal voltage should be approximately 1.35 V when twin heated oxygen sensor (HO2S) control is active. First injection period is calculated on the basis of the front heated oxygen sensor (HO2S) signal, then the rear heated oxygen sensor (HO2S) mean voltage is checked. If this is not 1.35 V then injection period calculations are adjusted to achieve the correct mean voltage for the rear heated oxygen sensor (HO2S).
A defective sensor may also have the correct mean signal voltage. For this reason the front sensor response time is also monitored. The engine control module (ECM) monitors how long it takes for the front heated oxygen sensor (HO2S) to switch from lean to rich to lean again. When the response time becomes too long for a number of diagnostic tests, diagnostic trouble code (DTC) EFI-435 Front heated oxygen sensor (HO2S), is stored.
The rear heated oxygen sensor (HO2S) response time is also checked. Fuel trim is carried out in a controlled cycle and if a signal from the rear heated oxygen sensor (HO2S) is not received within a set time diagnostic trouble code (DTC) EFI-153 Rear heated oxygen sensor (HO2S) is stored.
the front heated oxygen sensor (HO2S) has started control
the rear heated oxygen sensor (HO2S) has reached operating temperature
engine coolant temperature (ECT) exceeds 60°C
mass air flow is between 110 and 800 mg/tdc
engine speed is between 1,150 rpm and 4,000 rpm.
three-way catalytic converter (TWC) (diagnostic trouble code (DTC) EFI-443)
heated oxygen sensor (HO2S) preheating (diagnostic trouble code (DTC) EFI-521 or EFI-522)
mass air flow (MAF) sensor (diagnostic trouble code (DTC) EFI-121)
engine coolant temperature (ECT) sensor (diagnostic trouble code (DTC) EFI-123).
The three-way catalytic converter (TWC) stores oxygen found in the exhaust gases and uses it to make toxic gases less dangerous. The catalytic converter is a three-way catalytic converter (TWC) in which HC (hydrocarbons) and CO (carbon monoxide) are oxidized and NOx (oxides of nitrogen) are reduced. As the three-way catalytic converter (TWC) ages its ability to store oxygen drops. This reduces the conversion capacity of the three-way catalytic converter (TWC). To avoid dangerous emissions the engine control module (ECM) checks three-way catalytic converter (TWC) efficiency. This check is carried out as follows.
Two heated oxygen sensors (HO2S) are used to check the three-way catalytic converter (TWC) one upstream and one downstream of the catalytic converter. To determine catalytic converter efficiency the amplitude of the heated oxygen sensor (HO2S) signals is compared. During the catalytic converter diagnostic a controlled lean/rich fuel/air mixture cycle is carried out. When three-way catalytic converter (TWC) efficiency is good and the fuel/air mixture is normal, the front heated oxygen sensor (HO2S) signal switches between rich and lean (large amplitude) while the rear heated oxygen sensor (HO2S) signal is even (small amplitude).
When three-way catalytic converter (TWC) efficiency is poor and the fuel/air mixture is normal, the rear heated oxygen sensor (HO2S) signal switches between rich and lean (large amplitude). When this amplitude exceeds a certain limit for a number of diagnostic tests, diagnostic trouble code (DTC) EFI-443, Three-way catalytic converter (TWC) efficiency, is stored.