It sounds as though you have covered most things. One of the most critical parts of the emission control is the oxygen sensor (known as the lambda sensor). This transmits a signal to the ECU which in turn makes the necessary adjustments to the amount of fuel being injected, so that the lambda is then maintained within the design limits.

There are two different types of sensor; a zirconium oxide (which produces a small voltage at its terminals) and a titanium oxide (which relies on changes of conductivity for its operation) and is supplied with voltage. The reason for explaining this is that the test procedures are different for different sensors, so I would suggest that you make sure you have the correct one fitted, and that you tester knows what type is fitted and is using the correct process.