2002 Ford Explorer

Here is a 2002 Ford Explorer with 134,462 miles on it. Yes, that is my fat finger in the photo. The shop owner called me in for an intermittent or no communication with the PCM. This was preventing the vehicle from passing state inspection. There were no real driveability issues with this vehicle. The shop and the owner just wanted to get it to pass state inspection. The shop owner has tried two different scantools and the state inspection machine. All having communication issues. I plugged in the Ford IDS factory scantool and had no issues communicating. Plugging in an aftermarket tool I have I was greeted with no communication just like the shop owner said. Ok, lets get going here.

 

 

The first thing I did was to hook up my DLC BOB. I got mine from Aeswave. It is really a nice tool when dealing with communication issues. Upon hooking up I can see from my led indicators I have power at pin #16 at the DLC and grounds at pins #4 and #5. The data buss on this vehicle for PCM communication is SCP (Standard Corporate Protocol) on pins #2 and #10. I immediately see that pin #10 is modulating and pin #2 is not. Lets talk about this data buss.

SCP data buss is a two wire data buss. The two wires are for redundancy. One wire is pulled high and the other is pulled low. They should be mirror images of each other although moving in opposite directions. From the diagram you can see that on this early build (check production date) there are three modules on the data buss. The PCM, EATC (which this vehicle had), and the Instrument Cluster. Lets get a scope on those data lines.

I see issues already. I see Terminal #10 full of activity and Terminal #2 is not a mirror image. I also am not pleased with the amplitude of the signals. SCP is typically a 5 volt amplitude signal. Lets zoom in.

I zoomed in when we did have activity on both wires. A sloppy signal but pretty much a mirror image. Now what. Do I have a module causing problems on one leg of the SCP? What about the low amplitude? Do I really want to start popping out an instrument cluster. I quickly look for any type of aftermarket device such as an alarm or remote start tied into the SCP circuit. There was and I removed it and still had same issue. The DLC is mounted vertically on this vehicle. I unbolted it so I could get a good look at it.

I see something that catches my eye immediately.

 Terminal #2 is spread. In fact all the terminals on the top row are spread open. Years of scantools being put on the DLC and then yanked off at an angle spread the terminals apart. This DLC is mounted vertically and that is what contributed to this. I quickly check my theory by using a spare DLC male pin I use to check terminal tension and that confirms my theory. I gently squeeze terminal #2 down a bit and recheck my scope pattern.

Much better. More importantly hooking up various scantools yields communication every time. I am still perplexed by the low amplitude and the ragged signal. I have scoped this signal before and it never looked like this. I advised the shop owner that the DLC should be replaced with a quality replacement pigtail assembly. I give him a part number. Now why weren't the aftermarket scantools communicating and my IDS did.

The reason is that the aftermarket tools will initiate communication through pin #2. Where the IDS will be a little more forgiving and will communicate on pin #10 as well. Remember, the redundancy of the SCP buss. Engineers built that in in case one leg goes open or shorted. As I drive away from the shop the low amplitude/ragged pattern of the data buss is gnawing at me. Is there something wrong with my scope? I am reviewing my testing in my head on the way to the next job. Those that know me, know that this is eating away at me right now. I own a similar truck with a SCP buss. When I get home I will check it. That night I get home and check the SCP data buss on my own truck and get the same low amplitude/ragged pattern. At this point I am thinking it is a tooling issue. I then realize that I had my filters set to "on". Using filters is great for filtering out some noise but can through you off on some signals. Taking the filters off nets me this proper pattern.

That is more like it. The lesson here is know your tooling and how it operates during some applications. The other is don't overlook the obvious such as spread terminals.