OK, So you have got your first EOBD scan tool, You have read the manual, and are ready to go tackle the dreaded engine light on your car. You plug the scanner into the port in your car and do the first scan, the tool comes up with 3 trouble codes, one is a problemwith coolant temp circuit, one is MAF related and one is O2 sensor heater circuit, are there three problems with the car?

This is where most first time users go wrong, chances are there are not 3 problems with the car but only one which is causing the management light to come on, many inexperienced users automatically think if the scanner shows a MAF fault  “it must be the Airflow meter” which is not necessarily the case, it might have been disconnected in the past or the wiring / plug could be corroded which would all show a MAF fault. Many airflow meters have been bought and fitted with the problem not cured and the DIYer has given up and sent the car to a garage to be repaired where they have paid for the car to be repaired and the price of the airflow meter on top, could come to a hefty bill,  hardly a way to save money is it?

Any of these codes could have been logged in the past and stored in the ECU memory. Usually the best procedure is to note the codes, (write them down, you wont remember them!) or if the Scantool supports it store the diagnostic session for future reference, and then delete the codes stored in the ECU memory, then take the car for a drive or monitor the ECU for a day or two if the problem does not occur immediately. Most scanners will have an option to look for “pending codes” , what are pending codes I hear you say, Pending codes are trouble codes that have not materialised into full-blown codes and the engine malfunction light might not be illuminated yet, but the ECU has noted that there may be a problem and is monitoring the situation closely, this is a good way of catching any faults before they cause any problems with the engine management.

So the first rule is don’t assume the scanner has all the answers, maybe in the past someone has disconnected a sensor and this would have stored a trouble code. It is always best to clear any codes found first time and see which codes return and concentrate on these problems. Another useful feature is the Freeze Frame function which we will cover next time.

An ideal first time scantool is the Launch Creader Vi as it has the oprion to save up to 29 scans in the tool memory, these can be bought here www.scantool-direct.co.uk