Ralph , I am just thinking that as yours is 2002 model you probably have the metal canister type fuel filter so you cant easily have a look at the sediment the same as the post 2003 D5s with the plastic cup and paper insert . The number of codes that are produced with OBD11 and the Can system mean that for example for the 02 sensors you get one code for voltage too low or another for no signal etc so I would say the codes read out would be good enough to highlight a potentially faulty sensor but can also be misleading . Being an electronics & control engineer from the jurassic period I am happy enough testing sensors individually as the way they work hasnt changed much since then and most of what you find on a car seems to me to work the same way as sensors you would find on a production line or in an industrial process control system (its the actual control system / ECU and data transmission which is still a mystery to me) , you get a voltage or no voltage or some voltage in between which can mainly be easily measured using a cheap multimeter , some sensors also need a voltage input . O2 sensors can be tested using the heat from a gas flame on your cooker and should give a range of 0.1 to 1V or more but you also risk damaging the sensor so this is a last ditch approach . Front 02 sensor switches five or more times a second and the rear less than once every few seconds when its working in the cat , you cant see this with a cheap multimeter but you can using an old oscilloscope bought off ebay , some of these cost thousands of pounds years ago and now you can pick the same one up for £20 , most of these are not really suitable for auto electronics but with patience they work and so far I dont think I have damaged anything and I dont want to invest in a dedicated item such as a Picoscope which costs over £500 however if I had the money one of these seems to me to be a viable alternative to the official Volvo diagnostics which would cost thousands of pounds and has the benefit of working on any make of car . You can download OBD11 basics free of charge at scantool.net and this will apparently do basic engine diagnostics giving live data but as far as I am concerned this would cover 90% of what I need , I have done it but have not been able to get it to work on my D5 but at least I dont seem to have caused any damage by plugging it in , you do however run the risk of completely wrecking the ecu according to some experts so you use it at your own risk , you need an older lap top with serial port the modern ones dont have one (you can use a serial / USB emulator but I believe these are not reliable ) . The internet has loads of free information on the testing of various sensors. A more basic approach for example with the MAF is just disconnect it and take the car for a drive and then reconnect it , did that with mine in January and it cured a long standing problem that has not come back although I find it hard to believe that its really cured as I am relying on the problem having been a dirty connection and I cant even see which one it was . As you may have gathered I have got past the stage were I have any worries about connecting into the electrical system as I was seriously going to just sell the car in January as a non runner but its running great now and generally speaking I have so far found the electrical system although problematic quite resilient to tinkering about with .
|