Diagnostic warning light

I have recently been getting the diagnostic light flash on a more frequent basis? I have had the car GTA turbo for some 12 years and have had the diagnostic light flash occasionally, but not that often. It sometimes stay's on until it automatically resets, but with no affect on the engine performance.
Within the last 3-4 weeks I have noticed that the light has been flashing on more regularly especially when cold - when the temp warms up the flashing seems to stop. There has been no affect on performance even when the light comes on?

Is there a common symptom of the diagnostic flashing, especially when cold? What sensors could do this?

My first thought is that it may be the cold start cooling sensor in the thermostat housing starting to break down? I had a similar problem some years ago, and when the car was plugged in to the diagnostic tester it displayed that the cold start sensor was faulty? I changed it, but it had no affect on the engine running, maybe it is starting to fail again? . Is there a simple check to determine if it is OK, or could it be something else that is more obvious?

The car is due for an MOT very soon and I am concerned about the emissions, it is always on the limit and I assume that any fault with the sensor would not help?
I have never adjusted the potentiometer to bring the emissions in, choosing to leave well alone - has anyone had any success in adjusting the emissions using the potentiometer?

Any advise would be most welcome.

Thanks,

Jeff

very simple to adjust the co with the co pot.

you many could have saved more than a coulpe of litres over the last 12 years with it set correctly

Throttle pot on mine used to cause the diag ligh to flash. Go round the engine bay and wiggle the sensor wiring - you might see the light flash when you wiggle the offending item. I took a small cross-head screwdriver to the MOT station and the bloke let me adjust the pot while he was doing the emissions test.

Throttle pot on mine used to cause the diag ligh to flash. Go round the engine bay and wiggle the sensor wiring - you might see the light flash when you wiggle the offending item. I took a small cross-head screwdriver to the MOT station and the bloke let me adjust the pot while he was doing the emissions test.

Me too, it was VERY high and the MOT tester allowed me to adjust it. Only thing I changed since last MOT was to install a variable rate fuel regulator and to turn the pressure up, so I was not surprised..... which is why I also turned up for MOT with a small screwdriver.

I think DG told me that the co2 pot only adjusts the fueling at idle and low revs, so should have no affect on top end performance at all.

Simon thanks for the response.

How do you open the pot to be able to adjust it? I can see that there is a tamperproof seal but it appears very stubborn. I don't want to break the casing.
Any way, my problems are far worse that the CO2 reading for the MOT, the brakes failed on the way there!! ( see my response to brake overhaul) the main rear pipe burst.

The MOT tester is a good friend of mine and I don't think that the CO2 will be an issue, but I would still like to know how to adjust and have that option.
Thanks,

Jeff

pick out the tamper proof plug and then pull the outer cover off the co pot, you will then see a small flat headed adjusting screw. note, it only turns through 270 degrees, 'ish!