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The evolution of the ASD circuit
Posted to Technical Theory Forum on 6/12/2015 2 Replies

Disclaimer: I have theorized how this system works based solely on wiring diagram architecture and there is the possibility that the information is slightly inaccurate. Given the complexity of computer networking and vehicle wiring I am sure there are other possible explanations for how this system works. Please feel free to add your own insights, experiences and knowledge to the post so we all may learn from the discussion.

The vehicle listed above arrived with a complaint of poor shifting and engine cut off. SES light was active and codes found in engine control were P0406 and P0688. Initial test drive confirmed the given symptoms and vehicle shut down 4 times on a 1/4 mile test drive. While monitoring ASD PIDs during the test drive I noticed that ASD power would go low intermittently and then the vehicle would shut down. SES light was active and codes found in engine control were P0406 and P0688. And then Somedata throws some misleading information into the scene.

According to the trouble code description and test procedures for P0688 it shows that there is an ASD relay to test. This was not true for our case. We reviewed the wiring diagrams and found that the power for the circuit is provided by the Module-Totally Integrated Power (I will use IPM for short.) Apparently this separate module is responsible for the control of ASD power distribution and is in communication with the the CAN-C network. The other thing I noticed was that the layout of the ASD circuit is different from previous ASD circuits were this one supplies power to injectors and ignition coils only. I have been used to seeing transmission and engine sensors/actuators receiving power from ASD. From study of the diagrams it seems that the PCM uses circuit K51 to signal the IPM to activate ASD power. The IPM will provide power on circuit K342 when ASD control is sensed and allow for injectior and ignition coil power to flow.

With this information in mind I connected two channels of a lab scope directly to the back of the IPM, one to the ASD control and one to the ASD output. Upon test drive this is what was captured at point of stall. 2006 Dodge Ram 1500 SLT, Waveform

From my limited experience it appears as if there is a short to ground on ASD output (Yellow trace.) Either the IPM ramps up output to overcome the short or the short goes away. Then about 2 seconds after the output voltage goes to ground the PCM deactivates ASD control (Green trace goes to Bat+) by releasing the pull to ground. I wanted to test this theory so I devised a test.

Using a fused jumper wire while the engine was at idle, I created a short to ground on circuit K342 and noted how the IPM/PCM responded. Here is the result 2006 Dodge Ram 1500 SLT, Waveform

This pattern was consistent with the original capture so I began to look for a damaged wire in the engine harness. At first I took just a cursory look at the harness by inspecting high probability areas and pulled harnesses around in order to get a better look with a mirror and my bore scope. While there where several holes throughout the conduit on both the engine and transmission harnesses I did not see any shiny copper like I am used to seeing. So I decided to test with a different method.

There is a connector about half way through the harness (C130) that has easy access and allows for the connection of an amp clamp at that point. So I figured that I would split the circuit and use amperage spikes to help locate the suspected short to ground. Once I had my test equipment hooked up and test drove the vehicle all of the symptoms were no longer present. The vehicle shifted great and did not shut down at all. So what now? I have to believe that during testing I disturbed the problem wire/component. From where I was sitting I could have disturbed the problem when I lifted the IPM to back probe or when I moved the harnesses for inspection. From here I was thinking it was still possible that a component was internally shorting but without symptoms there would be no way to absolutely identify which component. However damaged wiring is by far the most common source of these types of problems in our bays. I wish I would have taken the amp readings first.

So I doubled down and removed the engine harness for a full inspection. After combing the harness over the only thing I could find were 4 wires that had signs of abrasion but not so deep as to leave copper visible. One of the wires was part of circuit K342. With K342 powered I could take a meter and lightly press on the insulation to get a 12v read. This portion of the harness rests on the plastic part of the intake manifold and very near (if not on) a braided ground strap. While one could imagine the stray metal strands of a half inch ground strap poking this wire, I still find it a long shot. I removed the damaged wire sections, soldered in new wire and repaired all harness conduit damage. And as you could imagine the symptoms did not return and the vehicle has been on the road for a few days now.

Should I sleep well at night or be looking over my shoulder for this to return? Also here is a close up capture of the original ASD short. 2006 Dodge Ram 1500 SLT, Waveform The oscillations are what scare me as I kind of think that it could even be a coil or injector shorting internally. Time will tell.

Jonathan Haney
Jonathan Haney
Birmingham, Alabama, USA

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car Vehicle Data

2006 Dodge Ram 1500 SLT 5.7L

Engine5.7 L
Trans5-speed Automatic (Electronic)