Here is one 2001 Nissan Pathfinder with 141,893 miles on it that is due for state inspection. The dilemma is the vehicle has the dreaded P1320 code for primary ignition. This is a very common code on Nissan vehicles with COP (coil on plug) ignition. There are three items that I see that will cause this code. One is bad COP units (more on this later), wrong spark plugs, and someone has tied the rpm input for a remote start into one of the COP units. The shop owner asked me to look at this because the customer cannot go for 6 new COP units. He needs a definitive answer on how many COP units are bad and if other issues are at hand. The code set criteria for this code is a little misleading. Basically, it says that there is a missing primary signal. So, this vehicle should be missing, right? Well, this vehicle runs well with no apparent misfires. Time to pull a wiring diagram.
Here is two out of three pages of wiring for the ignition system. It shows that the power for the COP units comes from one contact of the ECM relay. I am only showing three of the six COP units. Those of you that know me and follow the blog know where I am going next. What is going to show me all six COP units in great detail.
Out comes the low amp probe. I make jumpers for both contacts of the ECM relay and I am going to trigger off of #1 COP control circuit.
You don't have to be a scope jockey to see that two amperage patterns are different from the rest. The yellow trace is the coil amperage and the green is the #1 trigger. Forgive my forgetting to zero my probe. Let's add the firing order which is 1-2-3-4-5-6.
As you can see cylinder #1 is lower than the rest and cylinder #4 is higher. These are our two odd men out. Even the pattern at this timebase is not the same as the other four COP units. A good healthy COP unit on this application is typically 6-8 amps. Number 1 is at 4 amps and number 4 is at 9 amps plus. Lets look at these two and a healthy one closer at a better timebase.
Here is number one. Looks to me that there is an issue with this COP unit that is also affecting the trigger. More evidence to condemn the COP unit. Let's look at number four.
A couple things become apparent here. The amperage is high and the ramp is rather straight. Not, what I typically see. Let's look at a good cylinder.
Now, that is a typical Nissan COP waveform. Notice the ramp pattern and amperage. Again, forgive me for not zeroing my probe.
So here we are twenty minutes later and we have a definitive answer for the shop owner. I advised him that cylinders #1 and #4 COP units are the reason for the P1320. I also advise him to check the plugs while he is there. At this point I also tell him do not be suprised if these COP units at #1 and #4 have been changed and are aftermarket units. Sure enough the shop owner calls me the next day and tells me both units were recently changed with aftermarket units. He installed OE units, checked the plugs for proper brand and gap, and test drove the car. He was able to run and satisfy all the monitors for inspection and both he and vehicle owner were very happy. The MIL was out and a sticker was issued. At this point here goes my rant. The aftermarket in it's ongoing quest to provide "cheap" parts has shot itself in the foot. I see this time and time again. Quality doesn't cost it pays. The extra coin for an OE part is money well spent. Here is a prime example.
