This article will explain one of the most practical applications of Mode $06. The vehicle has a misfire but the MIL is not ON. It is a used car trade in with 120,332 miles and the repair history is unknown. The first obvious step is to scan it for codes. using a Generic scan tool to check the PCM and finds a P1000 DTC. This tells us that the DTCs have recently been cleared along with the Freeze Frame and other information. This DTC indicates that all the Monitors have not completed. Now we’ll the truck out for a test drive and after the test drive we determined that it runs well at this time. However, once in overdrive with the torque converter locked, you can feel an intermittent misfire of some sort. We have now verified the problem, but now we need to track down which cylinder. The task of identifying which cylinder or cylinders are misfiring is usually pretty easy. Since this is a Ford truck, we do not have the benefit of a misfire data screen. Using a stall test in the shop only gets the vehicle to act up very intermittently, not gonna find it this way, huh???
Well let’s exit the vehicle specific section of the scan tool and enter the Global OBD II section then select Mode $06 (sometimes called Non-Continuous Monitors) and look at the misfire section. On this vehicle it is TID $51 and CID $01 – $08 correlating with the individual cylinders. It shows that all the cylinders are passing but there is more information available. We definitely know that one or more of these cylinders are indeed misfiring. Note: Ford service information indicates that the TID is $53. In this case, the scan tool displayed it as TID $51. This is a common issue but does not prevent the use of this data. The scan tool will display one or the other, followed by 10 CIDs; one for each possible cylinder location.
The technician looks one step further into Mode $06 and finds a clue. While cylinder #1 was indeed misfiring, it didn’t quite make it high enough to put it into the Fail category. He scrolls through the corresponding data for the other cylinders and they all have a current value of zero, so he feels relatively confident that he has found the problem.
Looking at the picture above we decide to hook a lab scope to the primary of cylinder #1, and observe the ignition pattern which is normal. However, this is not surprising since the problem isn’t occurring all the time. Now take a look at the picture below. After several attempts, we finally obtain a capture of the misfire occurring. It is definitely an ignition issue, so we install a “known good” coil and a new spark plug, just to cover any possibilities of carbon tracking, fouling, etc. Good thing the misfire is on number one since cylinder #1 is easy to get access to.
We decide to go one step further and performs a relative compression test with his lab scope to make sure that there is no engine damage.
To perform this test, disable the fuel system (in this case the easiest method was to tap the inertia switch), and clamp a high amp current probe around the battery cable. The technician leaves Channel A lead connected to the #1 coil primary signal l and connects the current probe to Channel B.While cranking the engine over, the relative compression on all eight cylinders is represented by the increase in starter current as each piston approaches TDC. This waveform indicates that that the engine is in good mechanical condition. The ignition waveform returns to normal after installing the coil and plug. The truck is running smoothly and the we decide to call it repaired at this time. We takes the truck out for one last thorough test drive, note that it runs smooth, and check Mode $06 again.
FIXED, I know this would be easier with a distributor style ignition system but today most vehicles are coil on plug ignition systems and it’s just too costly to start changing ignition coils or all ignition coils and plugs, even though sometimes your customers will make it easy this way. With these skills you can at least be confident in which cylinder is causing the misfire regardless of how you go about repairing it.