Why does an engine check light come on

[obi_waynne]

What are the usual reasons for an engine check light appearing on a dashboard?

Without a diagnostic tool which things should be checked and in what order?

Have you ever had an engine check light come on? I did once but it was actually caused by bad wiring which was shorting out multiple engine sensors, it was a pig to track down but we got there in the end.

 

[pgarner]

disconnect the battery for 10 mins - making sure you know your radio code of course. to see if it clears the light.
if not then time to fault find or get diagnostic tool on to give you an idea
if it does go off most ECUs will still store the code for future scans.

ive had one on and off for a year. random things such as central heating lock overheating, speaker to ground etc. all caused by water getting into a electrical block and causing issues with the canbus.
one that allways showed up however was a EGT sensor. However anytime it went into the garage they ran it through the range with no issues found. turns out its a poor design and the wire can break. when stopped the wire makes contact again and runs through range.
changed ity out monday and so far so good. a couple months of no issues and ill get the remap booked

 

[admin]

You can get fault code readers off the web so cheaply now there is little excuse for just swapping out parts at random. You can even get them as Iphone and android apps with a bluetooth OBDII connector, the more sophisticated ones will actually reset the fault codes.

It is usually something electrical in my experience.

 

[T9 man]

My Saab is very fussy and will turn the ECL on if the moon is not quite in the right place or another period drama is shown on the tele :blink:

I bought an RAC fault code reader which will reset the ECL, the best £70 I have ever spent.

 

[HDi fun]

The ECL is a very general beacon to be honest. You do need a reader to diagnose the cause in any car. Even if you resolve the fault by trial and error many ECUs need to be forcibly reset and this does involve the use of some auxiliary electronics

 

[Jakeymd]

My Saab is very fussy and will turn the ECL on if the moon is not quite in the right place or another period drama is shown on the tele :blink:

I bought an RAC fault code reader which will reset the ECL, the best £70 I have ever spent.

I have the android one of these, it's an excellent bit of software. Going to start using it alot more in a couple of weeks when my commute goes from 5 minutes to 20 minutes.

 

[turbonutter69]

Just need a little bit of wire for the Nissan Primera. You can read fault codes and reset the ecu with just a bit of wire.
Quite a bit cheaper the the 70 quid Nissan want for them to do it.

The ECL is a very general beacon to be honest. You do need a reader to diagnose the cause in any car. Even if you resolve the fault by trial and error many ECUs need to be forcibly reset and this does involve the use of some auxiliary electronics

 

[Country Bumpkin]

Something to consider when you have found the reason for your 'check engine' light. In general, fault codes are not a specific means to an end.
Let's say for instance you detect a fault, via using a code reader, to be the throttle position sensor. The fault may not necessarily be that component, it could be a fault anywhere between the ECU and the throttle position sensor, this includes any wiring, connections or other readings used by that component.
What your code reader is telling you, is that component is not working correctly, not why it is not working correctly.
Before purchasing a replacement sensor, physically check the sensor and it's feeds by a fault finding process as generally described in most workshop manuals for your car.
Some items are exact, just don't go wasting money until you are 100% certain.
There is also a case where more than one component can be at fault but have one common end result.
Manuals are also available for a reasonable fee, on-line.

 

[Country Bumpkin]

One more thing to add. When multiple fault codes are showing, it is usually, not always, a faulty ECU itself.