Will a Bad coil throw an SES light?
06-29-2012, 11:45 AM
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Will a Bad coil throw an SES light? Ever since I bought my car last fall it has at times felt like it was missing on one of the cylinders. It used to happen just very now and then and now it happens all day long. I changed the plugs and wires and it didn't fix the problem. So I'm guessing it must be one of the coils? But my SES light is not ever on, and I know the light itself is working. Any advice would be appreciated. Thanks
06-29-2012, 12:17 PM
#2
A bad coil will not set an SES light unless it causes enough misfire to set the misfire counter. If it were to do that you could pin it down to that one cylinder and then trade that coil with another one to see if the problem stays in the same location or follows the coil.
You can test the coils for resistance but there is not a way to test their output without some some sort of scope or higher end diagnostic tools. A regular scan tool wont do you much good when trying to diagnose a coil issue.
You can test the coils for resistance but there is not a way to test their output without some some sort of scope or higher end diagnostic tools. A regular scan tool wont do you much good when trying to diagnose a coil issue.
06-29-2012, 03:29 PM
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Find someone that has a scanner that is capable of counting individual cylinder misfires. If you feel like one is missing it will show more misfires than the other cylidners. As stated, swap coils with one of the other cylinders to see if the problem follows the coil. If so, the coil is bad. If not, wire or plug is bad or there is something going wrong internally. (Or you are misdiagnosing it.)
A bad coil will not in and of itself cause a CEL. The computer counts misfires according to crank deceleration. The resultant misfires of a bad coil will be what sets off the CEL. If it has enough misfires it will light up. I have heard my LS2 miss as a result of bad plugs twice in the past before it ever set off a CEL. It was obvious as day to me which cylinder was missing once I saw the misfire counters going up in HP Tuners yet the computer had still not reached its DTC threshold.
A bad coil will not in and of itself cause a CEL. The computer counts misfires according to crank deceleration. The resultant misfires of a bad coil will be what sets off the CEL. If it has enough misfires it will light up. I have heard my LS2 miss as a result of bad plugs twice in the past before it ever set off a CEL. It was obvious as day to me which cylinder was missing once I saw the misfire counters going up in HP Tuners yet the computer had still not reached its DTC threshold.
