My 320sl is showing the dreaded engine warning light. I have been told it could by a lambda sensor down. How many has it got? I can see one either side of the cat on both downpipes. Does the diagnostics identify the faulty one? What else could be causing the fault please?

 

The "check engine" light could be lit for a thousand reasons. It is the omnibus warning that something is amiss in the engine or transmission. If there are no symptoms of a problem (engine missing, smoke from the exhaust pipe, knocking noise) it might very well be a sensor. In my recent experience, the light came on because a vacuum pipe from the brake booster to the MAF had broken.

You cannot assume the light is a lambda sensor problem. The only way you can find out is to have someone read the fault codes using an OBD II scanner. They will tell you exactly what the problem is. If it is a lambda sensor, it will tell you which one. In the United States, several auto parts stores will read the codes for free. I'm not sure whether the same is true in the UK. If it isn't, then a repair shop or a dealership is where you go. The charge for diagnosing the source will probably be minimal, although some shops will not diagnose without also doing the repair.

You will be ill-advised to change out parts without a firm diagnosis. You may replace perfectly good parts for no reason. Once the repair is effected either by you or a shop, the "check engine" light must be reset--again by someone with an OBD II scanner.