Aging of O2 sensor upstream of TWC (G3/3, G/4), correction variable exceeded | ||
1A | Fault code ( Readout on generic scan tool) | P200C Right O2 sensor upstream of TWC (G3/4) (-) P207F Left O2 sensor upstream of TWC (G3/3) (-) |
1B | Engines 112, 113 as of 1/01 Fault code ( Readout on generic scan tool) | P200C-[1] Right O2 sensor upstream of TWC (G3/4), dwell time too long (-) P200C-[2] Right O2 sensor upstream of TWC (G3/4), dwell time too short (-) P207F-[1] Left O2 sensor upstream of TWC (G3/3), dwell time too long (-) P207F-[2] Left O2 sensor upstream of TWC (G3/3), dwell time too short (-) |
2 | Fault storage Actuation of the engine diagnosis indicator lamp (EURO3/4) 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 Limits 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 - catalytic converter temperature greater than 350°C - no high loading of activated carbon filter (lambda greater than 0.4) - no effect of a fault on the catalytic converter - 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. 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 engines 112, 113 there is one catalytic converter and one lambda control assigned to each cylinder bank.
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 variation of several measurements is too large, a correction variable (lag 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.