Heated Oxygen Sensor (HO2S) diagnostic
Two heated oxygen sensors (HO2S) are used in the Denso engine control module (ECM). The heated oxygen sensors (HO2S) are checked as usual for short-circuits and open-circuits. Diagnostic trouble code (DTC) ECM-2120 (front heated oxygen sensor (HO2S)) or ECM-2200 (rear heated oxygen sensor (HO2S)) will be stored if any of these faults occur. The probe heat elements are also checked. In the event of a fault, diagnostic trouble code (DTC) ECM-2110 (front heated oxygen sensor (HO2S), heating), ECM-2120 (front heated oxygen sensor (HO2S), probe control) or ECM-2210 (rear heated oxygen sensor (HO2S), heating) will be stored. In addition, probe control is also checked. In brief, these checks are carried out as follows.
The front heated oxygen sensor (HO2S)
The front heated oxygen sensor (HO2S), which is a linear type: Two checks where the switch over time between rich-lean and lean rich fuel / air mixture is checked. The diagnostic checks the response time of the front heated oxygen sensor (HO2S) when fuel shut-off is activated and deactivated.
The rich-lean check takes place when the fuel shut-off system is activated, on condition that the sensor current is below a lower limit (indicates rich fuel / air mixture). When the fuel shut-off system is activated, the sensor current usually rises (this indicates a lean fuel / air mixture). The lean-rich check measures the time taken for the sensor current to rise from a lower to an upper limit value. If the time counter exceeds a fault level without the sensor current having reached the upper limit value, the response is considered to be too slow; a fault marker is stored.
The lean-rich check is carried out in a similar way when the fuel shut-off system is deactivated. The difference is that the time taken for the sensor current to fall is measured. Diagnostic trouble code (DTC) ECM-210A (front heated oxygen sensor (HO2S)) is stored in the event of a fault in both of these checks.
In addition, the lambda value is also checked. This value must not deviate significantly from its control value. Diagnostic trouble code (DTC) ECM-210F (front heated oxygen sensor (HO2S)) is stored if the difference is too great.
Rear heated oxygen sensor (HO2S)
The rear heated oxygen sensor (HO2S), which is a binary type, is checked in the following way.
The control module checks the difference between the rear probe voltage maximum and minimum values. This voltage must not exceed 0.5 V. If the difference is greater, the control module takes an initialization value as its starting point. This is a maximum of 0 V and a minimum of 5 V. After this, the rear heated oxygen sensor (HO2S) maximum value must exceed the initialization value (0 V) for the probe voltage by at least 0.6 V and fall below the initialization value (5 V) probe voltage to the minimum value 0.1 V. If these limit values are not reached within approximately 5 minutes and the accumulated and actual probe warming has not reached certain limit values, the control module interprets it as a fault.
Twin probe control starts and is active when
- the front probe has started control
- the rear probe has reached operating temperature
Twin probe control is interrupted during fuel shut-off, during misfiring or in the event of a fault in
- the catalytic converter
- heated oxygen sensor (HO2S) heating
Scheme 192
The engine coolant temperature (ECT) sensor checks the temperature of the engine coolant. The temperature of the engine coolant is required so that the engine control module (ECM) can regulate
- the injection period
- the idle speed
- the engine cooling fan (FC)
- the ignition advance
- engagement and disengagement of the A/C compressor
- diagnostic functions.
The sensor is a negative temperature coefficient (NTC) type which is supplied with power from the control module (signal) and is grounded in the control module.
The resistance in the sensor changes according to the temperature of the engine coolant. This provides the control module with a signal of between 0.1-4.9 V. The lower the temperature the higher the voltage (high resistance). A high temperature results in low voltage (low resistance).
The engine coolant temperature (ECT) sensor is located beside the thermostat.
The engine control module (ECM) can diagnose the engine coolant temperature sensor. The sensor value can be read off using VIDA.
Scheme 193
The engine cooling fan (FC) has two functions. One is to cool the engine compartment, the other is to cool the condenser when the air conditioning (A/C) compressor is working.
The engine control module (ECM) transmits a pulse width modulated (PWM) signal to the engine cooling fan (FC) control module. The control module then activates the fan at one of three different speeds. The speed of the engine cooling fan (FC) is determined by the engine control module (ECM), depending on the coolant temperature (based on the signal from the engine coolant temperature (ECT) sensor) and the vehicle speed.
When the vehicle is stationary, the engine cooling fan (FC) is activated as follows
- the first stage is activated at approximately 105 °C and shut of at approximately 100 °C
- the second stage is activated at approximately 110 °C and shut of at approximately 105 °C
- the third stage is activated at approximately 115 °C and shut of at approximately 110 °C.
Note. The engine cooling fan may have a post-run of up to approx. 6 minutes after the engine has been turned off. The time for the fan's post-run depends on engine temperature, temperature in the engine compartment and pressure level in the AC-system.
| WARNING | Be careful since the engine cooling fan may have a post-run after the engine has been turned off. |
The engine cooling fan (FC) and its control module are behind the radiator.
The engine control module (ECM) can diagnose the engine cooling fan. The fan can be activated using VIDA.
Scheme 194
The mass air flow (MAF) sensor gauges the air mass sucked into the engine. It continuously transmits signals to the engine control module (ECM) about the mass of the intake air. This data is used by the engine control module (ECM) to calculate
- the injection period
- the ignition timing
- the engine load.
The gearbox control module (TCM) also uses this data for its gear shift calculations. This data is transmitted to the gearbox control module (TCM) from the engine control module (ECM) via the high speed side of the Controller area network (CAN).
The mass air flow (MAF) sensor is a hot wire type. Unlike other hot wire types, the mass air flow sensor in the Denso system uses a hot wire which has a ceramic casing. This eliminates the need for a clean burn function.
The mass air flow (MAF) sensor is supplied with battery voltage by the system relay and is grounded in the engine control module (ECM). The signal from the sensor is analogue and varies between 0.5 - 4.5 V depending on the air mass. Low air flow (low mass) results in low voltage, high air flow (high mass) gives high voltage.
The mass air flow (MAF) sensor is positioned between the air cleaner (ACL) housing and the intake manifold.
The mass air flow (MAF) sensor also contains an intake air temperature (IAT) sensor.
The engine control module (ECM) can diagnose the mass air flow (MAF) sensor. The signal can be read using VIDA.
Scheme 195
The outside temperature sensor detects the temperature in the surrounding air. The signal is used by the engine control module (ECM) as a substitute value in the event of a fault in certain components or functions and to control certain diagnostic functions.
The sensor is a negative temperature coefficient (NTC) type which is supplied with power from the control module (signal) and is grounded in the control module.
The resistance in the sensor, which provides a signal between 0.1-4.7 V, changes depending on the outside temperature. Low temperatures produce high voltage (high resistance), high temperatures produce low voltage (low resistance).
The outside temperature sensor is positioned in the left door mirror.
The engine control module (ECM) can diagnose the outside temperature sensor. The sensor value can be read off using VIDA.
Catalytic converter diagnostic
The three-way catalytic converter (TWC) stores oxygen found in the exhaust gases and uses it to make toxic gases more environmentally friendly. The catalytic converter is a three-way catalytic converter (TWC) in which HC (hydrocarbons) and CO (carbon monoxide) are oxidized and NOx (nitrous oxide) is 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. In brief, this check is carried out as follows.
Two heated oxygen sensors (HO2S) are used to check the catalytic converter; one upstream and one downstream of the catalytic converter. The main function of the heated oxygen sensors (HO2S) is to measure the oxygen content in the exhaust gases so that the engine control module (ECM) can maintain the engine fuel/air mixture at around lambda=1.
The catalytic converter diagnostic consists of two checks. The first checks how quickly the three-way catalytic converter (TWC) begins to operate, and the second is a response time check. When starting cold the control module checks how quickly the three-way catalytic converter (TWC) begins to operate. If the target lambda is already varying during this check, the following check is not carried out.
When the engine is at operating temperature, lambda variations are created (Dither function) by the diagnostic, adding a deviation to the target lambda signal which the fuel control system regulates towards. The deviation changes between positive and negative values so that the fuel/air mixture changes between rich and lean. The discharge through the three-way catalytic converter (TWC) is determined by studying the variation of lambda and the response from the rear probe.
On a poorly performing three-way catalytic converter (TWC), the deviation changes can easily be calculated by the rear probe response time. On an efficient three-way catalytic converter (TWC) this is more difficult, because the variations take too long to go through.