2005 Chrysler Town & Country Misfire
This vehicle was towed in to me. The customer says that he replaced EVERYTHING and it still misfires. The customer is a do-it-yourself-er and I'm sure most of you already know where this is going. The vehicle has new spark plugs, Spark plug wires, ignition coil-pack assembly, 3 new Injectors, and a new crankshaft position sensor. I was told the misfire did not improve or change in anyway after replacing any of these components.
I started off by scanning the vehicle. There was only one code in the PCM which was P2305 Ignition Coil #2 secondary circuit insufficient ionization. The code description in Service information states that this code will set if the PCM detects that the secondary ignition burn time is incorrect or not present. One Trip fault.
The vehicle is running very poorly and feels like more than just one cylinder is misfiring. The customer had the vehicle towed in because he did not feel it would make it to our shop because of how poorly it was running.
Since the code description is pointing to an ignition issue and I have a misfire condition, I went straight to testing the Ignition system. This system is setup with a coil pack assembly that operates on a waste spark strategy. There are 3 coils within the coil assembly. There are 4 wires going to this coil. One circuit is the shared battery voltage originating at the ASD relay. And the other 3 wires are the Ignition ground control circuits from the PCM for each coil. The wiring diagram is in figure 3.
I made my connections to my scope as Illustrated in figure 4. Channel A (Blue) is connected to Ignition Coil 3 control. Channel B (Red) is Connected to Ignition Coil 1 control. Channel C (Green) is connected to Ignition Coil 2 Control. And last, Channel D is connected using a low amp probe on the shared B+ circuit to the coil pack.
In figure 5 you can see on Channel D I have 2 missing pulses of current per 720 degrees of crankshaft rotation indicating 2 ignition events are missing. On Channel C in green you will see the circuit is stuck at battery voltage and not being pulled to ground by the PCM to energize the ignition coil. This is evidence that the transistor in the PCM has failed. A new PCM was quoted and the customer elected to not fix the vehicle at this time so I do not have an after (good) capture to share with you
This is a fairly routine diagnosis for a professional technician but I wanted to share the importance of testing the systems properly and thoroughly to accurately pinpoint the cause of the issue at hand. Our industry can be a busy environment to work in and sometimes we may be quick to pull the trigger before a complete assessment is made. Unfortunately that incorrect assessment was made by the customer prior to having it diagnosed properly and he may have considered a PCM replacement had he not already spent unnecessary funds on parts he may not have needed.
Great case study Brian! I would have only changed one thing, I would make you channel C connection at the PCM, that way if you see your battery voltage at that location you have confirmed that you have your B+ to the coil and that you have a complete circuit all the way to the PCM, eliminating the need to inspect and test the wiring from the PCM switched side of the coil back to the PCM. Other
I originally tested at the coil for quick access. When the affected circuit was confirmed I went to the PCM to not only verify circuit integrity but coil integrity. I kept my low amp live on the scope while tapping the circuit to groud to make sure the current ramp looks healthy. After that was confirmed, I verified proper powers and grounds at the PCM.
Nice job Brian! It's ironic you posting this. I have an 05 Town & Country to go look at Monday for a similar concern. Did yours have the NGC controller in the driver's fender well? I've seen ionization DTCs on Chrysler products as well. The one I have data on was from a 2008 Jeep Wrangler 3.8L setting P2308 (Ignition Coil #3 Secondary Circuit-Insufficient-Ionization). It was caused by a
Great post Brian. This shows why actual testing should be preformed on these vehicles. As these routines become the norm, you will be able to do them faster and faster making you that much more efficient. How long did it take you to come to this diagnosis? I'm guessing less time than it took to prepare this post.
If the coil trigger wire voltage is good at the pcm, I will tap the wire to ground at the pcm and watch the scope amps to see if the wire can handle the coil amp load. Ray
Ray I actually did this exact test to verify not only circuit integrity but also that the could isn't shorted (even though it's new) The last thing I'd want would be a few pulses take out a brand new PCM 😁
Oh absolutely. 10-15 minutes of testing and I was pretty confident it was needing a PCM. Also, having previous experience with this code I was pretty confident it'd end up needing a PCM. HOWEVER, one must assume anything. Test and confirm your suspicions always!
Excellent write up and great testing that seems most shops or even Diyers are not doing before throwing parts at it. Way to often I see other shops bring me problems that are fairly easy to solve with the right testing and using accurate equipment such as a scope. Good job