OBD Codes

B200F LH 2.4 1993 Both my cars have intermittent faults (see other thread). This one is less serious and is really only an irritation: Once about every 300 miles the Lambda light comes on, always when cruising at about 50 mph on very light throttle. There is no hesitation etc when this happens. Reading the codes has given, on different occasions: 2-2-1 = compensating for extremely rich or weak mixture at cruise. 2-3-1 = compensating for rich or lean mixture at cruise 1-1-3 = mixture incorrect, oxygen sensor wiring fault On each occasion I have cleared the code, and the car has then started up with no light, until it happens the next time. So it seems whatever it is is just a short blip, rather than a permanent fault. The plugs are a perfect colour, and fuel consumption is normal. I needlessly replaced the oxygen sensor a few months ago, having read that after a high mileage (eg 400,000 miles) it might be getting tired and due for renewal. It made no difference. Does this sound like a sensor fault? Obviously I have checked the wiring and connections, and they seem all right. Many thanks, Cliff

Hi Cliff, With the code readings that you are getting and the sensor being ok then the problem must be I think that the ecu is compensating for an air leak at the manifold ,(the lambda sensor is seeing a lean mixture) , by increasing the fuel supply. The sensor still sees a lean mixture however and the fault code is set. Could be at the exhaust manifold flange itself , or a crack in the manifold or down pipe. Temporarily plug the exhaust pipe with a cloth and spray a soapy solution over the manifold and look for bubbles. Do it on a cold engine so the solution doesn't evaporate too quickly. It doesn't take much of an air leak to upset the closed loop control of the system.

Thanks Georgerov, I'll investigate that. It's odd though that it only does it momentarily, rather than continuously, and will then be fine for several hundred miles of varied driving. The last time the light came on I stopped immediately, cancelled the code, and it has stayed off - done about 200 miles since.