Hi, I know the "Check Injection" error message is old message, march 2009. My wife had the same one yesterday, I went and had a look, had to buy a Haynes manual first. Checked the "Diesel engine fuel and Exhaust systems" chapter.
Checked the general information, for the main componants. The fault finding chapter, engine misfires or idles unevenly.
Both parts point towards the air filter, (cheapest part of the system to eliminate £13.90). Changed this, found old one clogged, leaves, a fag butt. Vacumed the box out, new one in, problem gone.
The air filter clogged up lowers the air intake must lower the air flow, which is being monitored by the air flow monitor.
The same problem existed in my car, citreon picasso, again checked the manual and went for the cheapest option, air filter, lack of maintenance on my behalf as you do, try and fix it when it breaks.
Mike, May 2010