Part 2
14 COMPREHENSIVE COMPONENTS MONITORING Contd.14.4 Intake Air Temperature (IAT) Sensor
14.4.1 General Description
If more than one intake manifold air temperature sensor is used, the additional temperature sensors are also monitored.
The monitor is based on the comparison of the temperatures measured at a cold start. On a thoroughly cooled down vehicle, the measured temperature values of the temperature sensors should all be in the same temperature range (approximately ambient air temperature).
14.4.2 IAT sensor after the throttle, Rationality check high / low, P305E
Monitoring Strategy
The intake air temperature measured after the throttle during a cold start is compared with the engine coolant temperature measured during a cold start, or with the intake air temperature in the intake manifold of bank 1 measured during a cold start.
Typical Enable Conditions
- "Comparison of the temperature sensors (cross check)" monitor completed
Malfunction Criteria
During each engine starting event, the measurement values of the intake air temperature and the engine coolant temperature are stored. When the enable conditions are fulfilled, the monitor is started. If the difference between the intake air temperature after the throttle and the engine coolant temperature that has been verified in the "Comparison of the temperature sensors (cross check)" monitor (alternatively: the intake air temperature in the intake manifold of bank 1) is greater than / less than or equal a positive / negative threshold value, the fault "intake manifold air temperature sensor after the throttle, signal irrationally high / low" is detected.
14.4.3 IAT sensor in the intake manifold of bank 2, Rationality check high / low, P00AB
Monitoring Strategy
The intake air temperature measured in the intake manifold of bank 2 during a cold start is compared with the engine coolant temperature measured during a cold start, or with the intake air temperature in the intake manifold of bank 1 measured during a cold start.
Typical Enable Conditions
- "Comparison of the temperature sensors (cross check)" monitor completed
Malfunction Criteria
During each engine starting event, the measurement values of the intake air temperature and the engine coolant temperature are stored. When the enable conditions are fulfilled, the monitor is started. If the difference between the intake air temperature in the intake manifold of bank 2 and the engine coolant temperature that has been verified in the "Comparison of the temperature sensors (cross check)" monitor (alternatively: the intake air temperature in the intake manifold of bank 1) is greater than / less than or equal a positive / negative threshold value, the fault "intake manifold air temperature sensor in the intake manifold of bank 2, signal irrationally high / low" is detected.
14.4.4 Circuit Monitoring Short to Battery/Ground or Open Circuit
Monitoring Strategy
The signal voltage of the IAT sensor is continuously monitored.
Typical Enable Conditions
- Time since engine start greater than defined threshold value
Malfunction Criteria
Short to ground, P0112:
If the signal voltage of the IAT sensor is less than a defined threshold value for a defined time period, a short to ground is detected and a fault is stored in the fault memory.
Short to battery or open circuit, P0113:
If the signal voltage of the IAT sensor is greater than a defined threshold value for a defined time period, a short to battery or an open circuit is detected and a fault is stored in the fault memory.
14.5 Ambient Air Temperature (AAT) Monitor
14.5.1 Concepts receiving AAT over CAN
Applicable only for test groups
General Description
The AAT monitor checks that the measured AAT value is valid. It checks that the CAN message is received & uncorrupted; that the AAT value received is valid and that the AAT is plausible.
Monitoring Strategy
The monitor comprises four parts:
1. CAN message check - if the CAN message containing AAT is not received, or is incomplete or corrupted, a fault is detected
2. AAT is compared to upper and lower limits; if outside of these limits an out-of-range fault is detected
3. Rationality check at cold start - immediately after a cold start, AAT is compared to Intake Air Temperature; if the difference between the two is outside of limits, a fault is detected
4. Rationality check at normal engine temperature - AAT is compared to a modelled value; if the difference is outside of limits, a fault is detected.
14.5.2 Short to Battery/Ground or Open Circuit
Monitoring Strategy
The temperature measured by the AAT sensor is continuously monitored.
Typical Enable Conditions
- CAN-bus active
Malfunction Criteria
Short to ground, P0072:
If the measured AAT is greater than a defined threshold value for a defined time period, a short to ground is detected and a fault is stored in the fault memory.
Short to battery or open circuit, P0070:
If the measured AAT is less than a defined threshold value for a defined time period, a short to battery or an open circuit is detected and a fault is stored in the fault memory.
14.5.3 Signal Transmission Fault
Monitoring Strategy
The signal transmission is continuously monitored.
Typical Enable Conditions
- Ignition On
- No fault memory entry for the AAT sensor
Malfunction Criteria
Signal transmission fault, U0423, U0323:
If the internal signal monitoring function receives an irrational signal from the instrument cluster (U0423) or detects an instrument cluster to which no AAT sensor can be connected to (U0323), an entry in the fault memory is made.
14.6 Comparison of the Temperature Sensors (Cross Check)
14.6.1 General Description
On a thoroughly cooled down vehicle, the temperature values of the following sensors are compared to each other:
1. Engine coolant temperature sensor
2. Intake air temperature sensor
3. Ambient air temperature sensor
After a long engine-off time period, the measurement values of the temperature sensors should be close to the ambient air temperature. If one of the sensor measurement values (3) differs considerably from the other two sensor measurement values (1 and 2) and these sensor measurement values (1 and 2) are close to each other, the sensor with the irrational value (3) is detected as defective.
14.6.2 Intake air temperature sensor, irrational signal, P0111
Monitoring Strategy
When a cold start is detected, the three temperature sensor values are compared to each other.
Typical Enable Conditions
- Engine-off time > threshold value (cold start detected)
Engine block heater detection:
- (Engine coolant temperature at engine start minus minimum temperature after defined time period) < threshold value
An engine block heater is used to heat the engine coolant of a parked vehicle. The engine block heater is an external source of heat that is not connected to the ECM and hence is not detected. An engine block heater heats the engine and hence also the interior of the engine unevenly, so that the conditions for a cooled down vehicle are no longer fulfilled.
After a cold start, the engine coolant temperature normally increases continuously when the engine is running. If, after a defined time period, the engine coolant temperature decreases, it can be concluded that the engine has been heated unevenly by an external source of heat (engine block heater). If an engine block heater operation is detected, the monitor is disabled.
Detection of intensive solar radiation (heat soak):
- Difference between ambient air temperature at engine start and ambient air temperature at a vehicle speed that is greater than a threshold value for a defined time period ≤ threshold value
OR
- Difference between intake air temperature at engine start and intake air temperature at a vehicle speed that is greater than a threshold value for a defined time period ≤ threshold value
Intensive solar radiation (heat soak) can heat the vehicle at engine-off unevenly despite a long engine-off time, so that the monitoring result is distorted. It can be expected that the ambient air temperature or the intake air temperature will increase or remain about constant when the vehicle is driven, after a cold start had been detected. If one of the temperatures decreases, it can be assumed that the sensor values had increased due to heat soak and the state of a cooled-down vehicle had not been present.
Malfunction Criteria
At engine start the sensor values for the intake air temperature, the ambient air temperature and the engine coolant temperature are stored. When the enable conditions are fulfilled, the temperature values are compared to each other. If the difference between the engine coolant temperature and the intake air temperature at engine start is greater than a threshold value, the first condition for fault detection is fulfilled. If the difference between the intake air temperature and the ambient air temperature at engine start is greater than a threshold value, the second condition for fault detection is fulfilled. If the difference between the ambient air temperature and the engine coolant temperature at engine start is less than a threshold value, the third condition for fault detection is fulfilled. If all three conditions are fulfilled, the fault "intake air temperature, irrational signal" is detected.
14.6.3 Engine coolant temperature sensor, irrational signal, P0116
Monitoring Strategy
When a cold start is detected, the three temperature sensor values are compared to each other.
Typical Enable Conditions
- Engine-off time > threshold value (cold start detected)
Engine block heater detection:
- (Engine coolant temperature at engine start minus minimum temperature after defined time period) < threshold value
An engine block heater is used to heat the engine coolant of a parked vehicle. The engine block heater is an external source of heat that is not connected to the ECM and hence is not detected. An engine block heater heats the engine and hence also the interior of the engine unevenly, so that the conditions for a cooled down vehicle are no longer fulfilled.
After a cold start, the engine coolant temperature normally increases continuously when the engine is running. If, after a defined time period, the engine coolant temperature decreases, it can be concluded that the engine has been heated unevenly by an external source of heat (engine block heater). If an engine block heater operation is detected, the monitor is disabled.
Detection of intensive solar radiation (heat soak):
- Difference between ambient air temperature at engine start and ambient air temperature at a vehicle speed that is greater than a threshold value for a defined time period ≤ threshold value
OR
- Difference between intake air temperature at engine start and intake air temperature at a vehicle speed that is greater than a threshold value for a defined time period ≤ threshold value
Intensive solar radiation (heat soak) can heat the vehicle at engine-off unevenly despite a long engine-off time, so that the monitoring result is distorted. It can be expected that the ambient air temperature or the intake air temperature will increase or remain about constant when the vehicle is driven, after a cold start had been detected. If one of the temperatures decreases, it can be assumed that the sensor values had increased due to heat soak and the state of a cooled-down vehicle had not been present.
Malfunction Criteria
At engine start the sensor values for the intake air temperature, the ambient air temperature and the engine coolant temperature are stored. When the enable conditions are fulfilled, the temperature values are compared to each other. If the difference between the engine coolant temperature and the intake air temperature at engine start is greater than a threshold value, the first condition for fault detection is fulfilled. If the difference between the intake air temperature and the ambient air temperature at engine start is less than a threshold value, the second condition for fault detection is fulfilled. If the difference between the intake air temperature and the engine coolant temperature at engine start is greater than a threshold value, the third condition for fault detection is fulfilled. If all three conditions are fulfilled, the fault "engine coolant temperature sensor, irrational signal" is detected.
14.6.4 Ambient air temperature sensor, irrational signal, P0071
Monitoring Strategy
When a cold start is detected, the three temperature sensor values are compared to each other.
Typical Enable Conditions
- Engine-off time > threshold value (cold start detected)
Engine block heater detection:
- (Engine coolant temperature at engine start minus minimum temperature after defined time period) < threshold value
An engine block heater is used to heat the engine coolant of a parked vehicle. The engine block heater is an external source of heat that is not connected to the ECM and hence is not detected. An engine block heater heats the engine and hence also the interior of the engine unevenly, so that the conditions for a cooled down vehicle are no longer fulfilled.
After a cold start, the engine coolant temperature normally increases continuously when the engine is running. If, after a defined time period, the engine coolant temperature decreases, it can be concluded that the engine has been heated unevenly by an external source of heat (engine block heater). If an engine block heater operation is detected, the monitor is disabled.
Detection of intensive solar radiation (heat soak):
- Difference between ambient air temperature at engine start and ambient air temperature at a vehicle speed that is greater than a threshold value for a defined time period ≤ threshold value
OR
- Difference between intake air temperature at engine start and intake air temperature at a vehicle speed that is greater than a threshold value for a defined time period ≤ threshold value
Intensive solar radiation (heat soak) can heat the vehicle at engine-off unevenly despite a long engine-off time, so that the monitoring result is distorted. It can be expected that the ambient air temperature or the intake air temperature will increase or remain about constant when the vehicle is driven, after a cold start had been detected. If one of the temperatures decreases, it can be assumed that the sensor values had increased due to heat soak and the state of a cooled-down vehicle had not been present.
Malfunction Criteria
At engine start the sensor values for the intake air temperature, the ambient air temperature and the engine coolant temperature are stored. When the enable conditions are fulfilled, the temperature values are compared to each other. If the difference between the engine coolant temperature and the intake air temperature at engine start is less than a threshold value, the first condition for fault detection is fulfilled. If the difference between the intake air temperature and the ambient air temperature at engine start is greater than a threshold value, the second condition for fault detection is fulfilled. If the difference between the ambient air temperature and the engine coolant temperature at engine start is greater than a threshold value, the third condition for fault detection is fulfilled. If all three conditions are fulfilled, the fault "ambient air temperature sensor, irrational signal" is detected.