Electrical Test
The purpose of this monitor is to diagnose the analogue input signal from the intake air temperature sensor (TIA).
The output from the intake air temperature sensor is compared to a calibrated maximum and minimum value. If it is less than the minimum value then the error 'short circuit to ground' is declared. If the sensor output is greater than the maximum value then the error 'short circuit to battery or line break' is declared.
Sensor Stuck Test
The purpose of this monitor is to diagnose a stuck input signal from the intake air temperature sensor (TIA).
The signal from the intake air temperature sensor is compared to the starting intake air temperature sensor. The maximum absolute difference is recorded during the drive cycle.
After the vehicle has reached normal operating temperature following a soaked start, a minimum operating time has expired and the vehicle has been driven a minimum distance, the value of maximum intake temperature variation is compared to a threshold. If insufficient variation has occurred then a failure is declared.
Sensor Plausibility Test
The purpose of this monitor is to check for a plausible change of the input signal from the intake air temperature sensor (TIA).
(An offset intake temperature sensor value is verified with the ambient temperature plausibility diagnosis.)
Accumulated mass airflow is calculated during the drive cycle. This is used to determine the engine has been sufficiently warmed for the ambient air temperature dynamic to be detectable. When sufficient mass airflow has been accumulated the engine operating conditions are checked. The intake air temperature is monitored during specific engine operating conditions for an implausible increase or an implausible decrease. If the temperature change during each check is too great a failure counter is incremented
When the failure counter reaches a threshold a failure is declared.
Downstream Sensor Diagnosis Phase
If the catalyst diagnosis has completed without any problem, the downstream sensor is treated as «good» and a sensor diagnosis is not necessary.
If a problem has occurred with the downstream sensor during the catalyst diagnosis, a sensor diagnosis is done.
If throughout the catalyst diagnosis phase, repeated several times, the downstream sensor has not reacted, the A/F closed loop mode is delayed in order to test the sensor.
If the downstream sensor signal indicates a rich (lean) mixture, the injection time is forced to lean (rich) until the filtered downstream sensor signal switches over or until the end of a delay. If this delay expires, the sensor is treated as failed. This may be a result of
- A leak in the exhaust line
- A damaged sensor.
Electrical failures (short circuit and open circuit of signal and heater) are detected during the «comprehensive components» diagnostics.
Catalyst Diagnostic RBM Summary
The performance ratio for the catalyst diagnostic will be tracked and reported to a Generic Scan tool (GST) using Mode 09 Info Type 08 Position 2. The performance ratio target for MY06 is 0.1.
The error detection is performed by the hardware. The following errors can be detected when the key is on
- Short to ground
- Short to battery voltage
- Line break
Resistance Test
Once the vehicle is running a set of diagnostic entry conditions must be met. These include a MAF window, catalyst temperature, battery voltage and engine speed.
If the entry conditions are met then the O2 sensor heater circuit resistance is compared with a threshold. If it is below the minimum or above the maximum threshold for a sufficient length of time then an error is set.
The error detection is performed by the hardware. The following errors can be detected when the key is on
- Short to ground
- Short to battery voltage
- Line break
Once the vehicle is running a set of diagnostic entry conditions must be met. These include a MAF window, catalyst temperature, battery voltage and engine speed.
If the entry conditions are met then the O2 sensor heater circuit resistance is compared with a threshold. If it is below the minimum or above the maximum threshold for a sufficient length of time then an error is set.
Diagnosis Phase
The sum of the periods is compared to limits values, to detect a failure.
As an example, the typical behavior of the period criterion versus NOx emissions are shown in the following chart
Scheme 223
Upstream Oxygen Sensor Response Diagnostic RBM Summary
The performance ratio for the upstream Oxygen Sensor symmetrical response diagnostic will be tracked and reported to a Generic Scan tool (GST) using Mode 09 Info Type 08 Position 4. The performance ratio target for MY06 is 0.1.
Diagnostic Monitoring Air intake system leak (block3)
A disconnection of the PCV hose from either the PCV valve or the intake manifold introduces an air leak into the intake manifold.
When this happens the throttle will naturally close and thus the MAF at the throttle (which is computed from manifold pressure drop across the throttle and throttle opening) will decrease. The mass airflow at the cylinder (which is computed from manifold pressure) will increase because of the air leak.
When the divergence of these two values reaches a threshold, an error flag is raised and fault code P1498 will be stored (the service information fault trees indicates PCV as a possible reason).
(Scheme 224)for an indication of the MAF divergence and the subsequent adaptive term response.
When an air leak in the air intake system is detected the engine speed is limited to 2000 RPM.
