Aging of O2 sensor upstream of TWC (G3/7 to G/10), correction variable exceeded | ||
1 | Fault code ( Readout on generic scan tool) | P207F Right O2 sensor upstream of TWC for cylinders 4 to 6 (G3/10) (-) P20A5 Left O2 sensor upstream of TWC for cylinders 7 to 9 (G3/7) (-) P20A6 Left O2 sensor upstream of TWC for cylinders 10 to 12 (G3/8) (-) P200C Right O2 sensor upstream of TWC for cylinders 1 to 3 (G3/9) (-) |
2 | Fault storage Actuation of engine diagnosis indicator lamp (EURO4) or CHECK ENGINE (MIL) malfunction indicator lamp | after expiry of test duration and fault no actuation |
3 | Checking frequency | Continuous |
4 | Checked signal or status | Lambda control, correction variable exceeded |
5 | Fault setting conditions Limit value of correction variable |
About 1.0 second (TV) |
6 | Check prerequisites | - engine speed approx. 750 to 2500 rpm - load approx. 20 up to 60% - lambda controls enabled - no fault in O2 sensor heater - TWC temperature higher than 380°C - no high loading of activated carbon filter (lambda greater than 0.4) - no CAN fault |
7 | | If faults are recognized at the same time for the O2 sensor upstream and downstream of TWC then it generally only the O2 sensor downstream of TWC which is defective. Also check whether the workshop relevant fault "O2 sensors downstream of TWC, no sensor state change" is stored. If the O2 sensor downstream of TWC is so defective that the sensor voltage remains slightly under the regulating threshold then the lambda control is enriched over TV. Monitoring of the correction parameter for the O2 sensor upstream of TWC then wrongly recognizes a defective O2 sensor upstream of TWC. If the correction parameter for the O2 sensor upstream of TWC is exceeded then the O2 sensor downstream of TWC will continue to be monitored. |
Scheme for two-sensor control
On engine 137 there is one catalytic converter and one lambda control assigned to every 3 cylinders.
Engine
Lambda control
Catalytic converter
Monitoring
Cycle duration
Monitoring
Limit values
O2 sensor
upstream TWC
O2 sensor
downstream TWC
Correction variable for lambda closed-loop control
Specified/actual value comparison
P07.61-0383-06
1 O2 sensor signal upstream of TWC
A Voltage threshold for
rich - lean transition (b) or
lean - rich transition (c)
2 Lambda control without correction variable
3 Lambda control with
correction variable (d), timing variation
(+TV) in rich direction
4 Lambda control with
correction variable (e), timing variation
(-TV) in lean direction
Check procedure
The engine control unit determines the lambda mean value from the signals of the O2 sensors downstream of TWC. This value is compared with a stored value for optimum exhaust emissions.
If the deviation is too large after a number of measurements, a correction variable (dwell time TV) is determined for the lambda control.
The correction variable (value for new O2 sensor approx. 0) makes it possible to compensate for aging of the O2 sensor upstream of TWC within certain limits. If the correction variable exceeds the limit value, the O2 sensor upstream of the TWC must be replaced.
In addition, allowance is made for the period of the signal supplied by the sensor upstream of TWC. If no sensor state change takes place, the lambda control is not active and therefore a two-sensor control is not possible either.
The effect of the firewall catalytic converters is monitored based on the O2 sensor signals downstream of the TWC.
P49.10-2071-06
Location of O2 sensors
156 Length compensating element
157 Firewall catalytic converter
158 Underfloor catalytic converter
G3/7 Left O2 sensor upstream of TWC for cylinders 7-9
G3/8 Left O2 sensor upstream of TWC for cylinders 10-12
G3/9 Right O2 sensor upstream of TWC for cylinders 1-3
G3/10 Right O2 sensor upstream of TWC for cylinders 4-6
G3/11 Left O2 sensor downstream of TWC for cylinders 7-9
G3/12 Left O2 sensor downstream of TWC for cylinders 10-12
G3/13 Right O2 sensor downstream of TWC for cylinders 1-3
G3/14 Right O2 sensor downstream of TWC for cylinders 4-6
A Cross connection