Plausibility Diagnosis

Plausibility Diagnosis
These diagnosis check that some data acquisitions from different sensors correspond to data acquisition from other sensors under given engine working conditions.

Idle speed control diagnosis
Engine speed deviation from the nominal engine speed set point is monitored when the vehicle is stopped.

If the engine is in idle state for a given time and in normal conditions of engine load, coolant temperature, battery voltage and canister vent valve opening and the difference between set point and actual value is too low or too high, then an error is raised.

Camshaft sensor diagnosis
The camshaft sensor signal presents 1 edge (rising or falling) per engine revolution. The position of these edges is known vs. crankshaft long tooth position.

A plausibility diagnosis is then performed in order to compare CAM and crank signals. The CAM edge must be in a window of crank teeth in order to declare the CAM signal as valid.

If CAM error is detected, sequential fuel injection will run with a constant injection phase of - 180 degrees CRK and the engine will run open loop. With 50%, the injection starts right, otherwise, it will impact engine responsiveness. For ignition, each coil is treated every TDC. Knock correction will take a constant value.

Intake manifold pressure sensor diagnosis
In certain conditions, it is checked that the MAP (manifold pressure) has a coherent value vs. engine speed and throttle opening. These conditions are:
- MAP too low at engine stopped (in these conditions, MAP cannot be lower than the minimum ambient pressure value).
- MAP too low at idle speed engine running (in these conditions, the engine cannot be run with too low manifold pressure)
- MAP too low at full load for low engine speed (in these conditions, MAP cannot be lower than the minimum ambient pressure value)
- MAP too high in deceleration (EMS calibration is tuned so that MAP target value is 200 hPa in deceleration).

In case of error on MAP acquisition, the MAP information will be built up by using engine speed and throttle position information.

Motorized throttle diagnosis controller diagnosis
In normal conditions, throttle set point and actual value must correspond within a tolerance given by controller performance in worst case conditions (response time, overshoot...).
If an error is detected, then MTC H-bridge is switched off and engine speed is limited at 2000 rpm.

Clutch switch diagnosis
When cruise is active (clutch switch is only used for cruise control deactivation), it is checked that the clutch sensor does not flag a de-clutched engine.

Coolant temperature sensor
After start, a modeled coolant temperature is calculated based on coolant temperature at start, engine speed and load while running, time spent in idle and fuel shut-off.

When model temperature (TCO_SUB) reaches the threshold for closed loop activation, closed loop must be activated. Indeed, TCO_SUB is tuned in order to rise much slower than TCO and so permits to monitor the plausibility of the coolant temperature information.

Air intake system diagnosis
This can be divided into 2 diagnoses:

- Diagnosis 1: detection of air leaks on air filter (before throttle).
Ambient pressure (AMP) is learned when engine is stopped from manifold pressure input and in full load by taking into account the air filter pressure drop. This pressure drop is known and calibrated in order to learn ambient pressure without error.







If an ambient pressure learning is performed just after start (driver went into full load), this AMP must be consistent with AMP learnt when engine is stopped. If an air leak is present in the air filter, pressure drop through air filter is under-estimated and so AMP will be over-estimated.

- Diagnosis 2: detection of air leaks in intake manifold (after throttle).
In the air path, 2 mass airflows are computed (1 @ throttle and 1 @ cylinder). In order to take into account engine to engine dispersions, an adaption will ensure the convergence of MAF @ throttle on MAF @ cylinder.

In case of air leak, the throttle will naturally close and so MAF @ throttle (which is computed from throttle opening) will decrease. MAF @ cylinder will increase because of air leak. When the divergence reaches a threshold, an error flag is raised.







In case of leak in the air intake system, engine speed is limited to 2000 rpm.