O2Fault code description - ME-SFI - ageing of oxygen sensor upstream of TWC - AD07.61-P-4000-07A

1	Fault code	P0133 right upstream of TWC
		P0153 left upstream of TWC
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	after two successive driving cycles with faults
3	Checking frequency	continuous
4	Checked signal or status	Signal of O2 sensor upstream TWC [KAT] Correction value exceeded Cycle duration too long
5	Fault setting conditions	approx. ± 1.2 s (delay time)
	Limits for correction variable Cycle duration for limit value Checking duration	> 5 s (mean value from 15 measurements) up to 190 s
6	Check prerequisites	Engine speed approx. 1000 to 2000 rpm Load approx. 15 % to 50 % Coolant temperature > 80 °C Catalyst temperature > 380 °C Lambda control enabled No fault in catalytic converter effect No fault in O2 sensor heater or aging Air pressure more than approx. 780 hPa (i.e. no test is performed above a height of approx. 2500 m)
7	After a repair, carry out tests and driving instructions	The tests 1 to 4 must be carried out together one after the other without switching off the engine. 1st Check O 2  sensor heater  Vehicle is stationary and in drive position P Coolant temperature > 80 °C Let engine run at 2000 up to 2500 rpm for approx. 2 minutes Then let engine run in idle for approx. 6 minutes 2nd Check aging of O2 sensor upstream TWC [KAT]  Drive vehicle in drive mode D for approx. 3 minutes at approx. 70 km/h on a straight road 3rd Check catalytic converter effect  Drive vehicle in drive mode D for approx. 3 minutes at approx. 80 up to 90 km/h on a straight road 4th Check self-adaptation of mixture formation.  Vehicle is stationary and in drive position P Let engine run in idle for approx. 3 minutes If the individual test is performed, this is displayed in the HHT as follows: If the test is passed without a fault, "-V-" is placed in dark (repair is successful). If the test is passed with a fault, "-F-" is placed in dark. After ignition OFF the tests are again restored (white field). Only after the test has been performed once again, the corresponding fields are once again placed in dark. Carry out a new test only after approx. 10 seconds ignition OFF.
8		Cycle duration of O2 sensor signal upstream TWC [KAT] too long: O2 sensor downstream TWC [KAT] is not monitored further Correction variables exceeded: O2 sensor downstream TWC [KAT] is monitored further If faults are detected simultaneously for the O2 sensor upstream and downstream TWC, usually only the O2 sensor downstream TWC is defective.

Diagram of two-sensor control 

Fig 1: Identifying Two-Sensor Control - Flow Chart

Courtesy of MERCEDES-BENZ USA

1. Oxygen sensor signal, upstream of TWC
   1. 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), time delay (+T_V ) in rich direction
4. Lambda control with correction variable (e), time delay (-T_V ) in lean direction

Fig 2: Identifying Oxygen Sensor Signal, Upstream Of TWC Graph

Courtesy of MERCEDES-BENZ USA

Test sequence 

The engine control unit calculates the lambda mean value from the signals supplied by the oxygen sensor 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 (delay 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 status change takes please, the lambda control is not active and thus two-sensor control is not possible.

The effect of the three-way catalytic converter is monitored with the oxygen sensor signals downstream of TWC.