PRE-RELEASE
Rear heated oxygen sensor (593)
| Rear heated oxygen sensor (593) |
| Location |
Rear heated oxygen sensor (593)
| Main task |
To diagnose the front catalytic converter, an oxygen sensor is mounted in the exhaust system after the catalytic converter. The sensor is called oxygen sensor 2 or O2S 2.
| Type |
| Connection |
| Pin No. | Signal type | Description |
| 1 | Power supply, B+ | Preheating power supply from preheating relay. |
| 2 | Control | Preheating's control. Preheating is grounded by ECM pins 61(B) and 62(B), which control preheating current. |
| 3 | Ground | Oxygen sensor's signal ground. Connected to ECM pin 19(B). |
| 4 | Signal | Oxygen sensor's signal. Connected to ECM pin 7(B). |
To quickly yield voltage after start, the oxygen sensor must be preheated. Grounding of the preheating circuit is pulse width modulated so that preheating output can be regulated.
Preheating is activated as soon as coolant temperature exceeds 30°C.
The control module estimates exhaust temperature based on load and engine speed. If exhaust temperature is high, preheating is switched off so as not to damage the oxygen sensor.
If the catalytic converter is damaged, its ability to store oxygen decreases. The normal oscillations of closed loop will then be detected based on the voltage from oxygen sensor 2. A DTC will then be generated. Diagnostics is run once per operating cycle.
In addition to catalytic converter diagnostics, the oxygen sensor values are also used to correct closed loop for minor faults in oxygen sensor 1.
The best emission values are obtained when voltage from oxygen sensor 2 is 0.6 V.
If, for example, voltage is 0.3 V, the engine runs somewhat lean. The closed loop correction factor will then lock in rich mode for a certain number of combustions before voltage from oxygen sensor 1 is allowed to have an effect again.
