Aging of O2 sensor upstream of TWC - fault code description ME - AD07.61-P-4000-07AA

		Aging of O2 sensor upstream of TWC (G3/3, G/4), correction variable exceeded
1A	Fault code	P200C Right O2 sensor upstream of TWC (G3/4) (-)
	( Readout on generic scan tool)	P207F Left O2 sensor upstream of TWC (G3/3) (-)
1B	Engines 112, 113 as of 1/01	P200C-[1] Right O2 sensor upstream of TWC (G3/4), dwell time too long (-)
	Fault code	P200C-[2] Right O2 sensor upstream of TWC (G3/4), dwell time too short (-)
	( Readout on generic scan tool)	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	after expiry of test duration and fault
	Actuation of the engine diagnosis indicator lamp (EURO3/4) or CHECK ENGINE (MIL) malfunction indicator lamp	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.

Fig 1: Identifying Two-Sensor Control - Flow Chart

Courtesy of MERCEDES-BENZ USA

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 (+T_V ) in rich direction
4. Lambda control with correction variable (e), timing variation (-T_V ) in lean direction

Fig 2: Identifying O2 Sensor Signal Upstream Of TWC Graph

Courtesy of MERCEDES-BENZ USA

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.