Lambda sensor installed at exhaust manifold is linear Lambda sensor and it senses O2 density of exhaust gas for accurate EGR control through fuel correction. It also limits smoke which is generated by reach air-fuel mixture at engine maximum loading condition. ECM controls pumping current in order to fit ?-value from linear Lambda sensor to 1.0.
Lean air-fuel mixture(1.0
Rich air-fuel mixture(0.9
This performance is the most active and fast at normal operating temp.(450°C~600°C) thus, in order to reach normal operating temp. and last at that temp., heater(heating coil) is integrated with Lambda sensor.
Heater coil is controlled by ECM as PWM. the resistance of heater coil is low when coil is cold thus, current through it increases while resistance is high when coil is hot thus, current decreases. With this principle, Lambda sensor temp. is measured and Lambda sensor heater operation varies based on the data.
P2251 is set when there is short battery or open in circuit (refer to DTC Detecting Condition).
Item
Detecting Condition
Possible Cause
DTC Strategy
Voltage Monitoring
Lambda sensor circuit
Lambda sensor component
Enable Conditions
Engine running
Threshold Value
Short to battery on 'Current Pump Line', 'Current Adjust Line', 'Virtual Ground Line', 'Voltage Nernst Line'.
Open on 'Virtual Ground Line'.
Diagnostic Time
2.0 sec.
Fail Safe
Fuel Cut
NO
EGR Off
Fuel Limit
Check Lamp
? value
0.65
0.7
0.8
0.9
1.01
1.18
1.43
1.7
2.42
Air
Pumping
current
-2.22
-1.82
-1.11
-0.5
0
0.33
0.67
0.94
1.38
2.54
Fig.1) CH-A is waveform of Lambda sensor power at IG KEY "ON" and Engine running. It fluctuates between 2V and 3V periodically.
CH-B is Waveform of Lambda sensor ground at IG KEY "ON" and Engine running. 2.5V is displayed.
Fig.2) CH-A is Waveform of Lambda sensor signal at IG KEY "ON" and Engine running. 2.5V is displayed.
CH-B is Waveform of Lambda sensor pump at IG KEY "ON" and Engine running. 2.5V is displayed.