I have been trying to eliminate a no spark issue with my 1997 Ram 1500 ext.cab 5.9 w/auto tranny for 4 days now. I replaced the ignition coil due case cracks, replaced to crankcase sensor after getting intermittent results when testing it out of tranny case, and replaced the PCM. All fuses check okay and I have power to #16 pin and ground to #4 pin on the OBD-2 connector. However, I have attached 2 seperate code scanners with the only results coming back saying "BROKEN LINK" prior to swapping out PCM with one scanner, then no communication after swapping PCM. I have two certified mechainic friends that have helped me try to diagnose this issue and between the three of us we are puzzled. I'm talking 60 years of combined mechanical brainpower. I have also noticed that my ASD relay doesn't seem to click/engage when key turns to run, but the starter relay will click/engage when key is turned to start, even after swapping relays. All sensors now operate correctly but I still have no power to coil when I do the backpin test with my LED tester. I also have no "check engine" light coming on, even after taking dash apart and replacing bulb just to make sure that the bulb did indeed work. At this point I would like to have any helpful information I can obtain on making a scanner communicate with the vehicle first and foremost. It worked in the past when I needed to scan, and like I said pin#4 and pin#16 test fine for power and ground on the OBD-2 connector.

 

Welcome to the site. I will move this thread to the second generation Ram section,
FF

 

In this case, this sounds like either the five-volt supply "may" be shorting to ground thus, causing the failsafe mechanism inside the PCM to initiate an AUTO POWER DOWN of the PCM itself (thus, no spark, no power to the ASD relay thus, no power to the EFI system etc). This is not to be confused with an Automatic Shutdown Event in which the PCM is still powered on. In this scenario, the PCM is totally shut down thus, NO BUS, COM error, etc etc.

This is an entirely different issue in which, the root cause in many cases is a shorted sensor, either internally at the coil or, externally at the harness level and, it's normally associated with the CKPS or CPS sensors, and O2 sensors and, one other sensor as well that runs off that supply. At current, I cannot recall which one- MAP. Yes, I believe it's the MAP sensor that is run off that supply as well on some years.

Now, when we look at what else will cause this same thing to happen:

- you may have lost a ground for the PCM itself or,

- the PCM supply input is reading low voltage thus, if and when there's a low voltage condition, the voltage to power the PCM is insufficient thus resulting in auto shutdown mode.

We have three possible failure modes and they are:

1. Low voltage condition

2. No power condition

3. Short condition

NOTE: In light of you're wondering why you have no power to the ASD relay at all / no clicking is heard: Do note that some of the grounds that are used to complete both ASD and FUEL PUMP RELAY CKTs are tied THROUGH the PCM and, at time of KEY <ON> event, the PCM is responsible for switching that CKT IN / OUT by means of a solid state relay internal to the PCM. The same is true for the coil driver CKT and the fuel injector driver CKT. The PCM controls those grounds so, if you've got a scenario of NO POWER at any time to either ASD or FUEL PUMP relay or CKPS or CPS, there's a high probability of a failure to either supply the PCM, ground it or, a short of the five-volt supply.

One thing to verify is if you've got power for 2-3 seconds or no power at all. In order to test that out:

-Disconnect the negative lead for 30 seconds to a full minute. Longer is better as I've encountered issues after 30 seconds to where, total discharge of PCM power was not achieved thus not clearing out all data.

-Reconnect the negative cable.

-Using a DMM, backprobe the COIL connector on the B+ side (HOT) GR/OR

-Attach ground to the headlight ground- clean before attaching to ensure good ground.

Have someone crank the engine and note ~12 VDC on display.

<IF> you see ~12V for 2-3 seconds of cranking, this indicates the PCM is NOT dead and is powered ON.

<IF> you DO NOT see squat:

Either there's no power TO the PCM or, there's a low voltage condition (voltage drop, loss, high contact resistance, corrosion are all possible causes) OR, the five-volt supply is shorted. NOTE: the meter that is used may also not be able to lock on a reading in that short of time thus, you may never see this voltage on the display. In that case use method No 2.

METHOD No 2:

-take a ignition wire off the coil and attach a plug to frame ground and watch for spark after you've reset the PCM again. Remember, if and when a failsafe event is triggered, the PCM must be reset in order to repeat the test and, you will have apx. 2-3 seconds to obtain a reading / results.

You will not see any voltage / arcing during this test if the PCMs five volt supply is shorted, there's a no or low power condition present at the PCM. FYI

So, once you test this far, you will know where to start rooting around.

CM

 

Thank you CM for the help. I'm taking the PCM back that I replaced the old one with in case it was a bad remanufacture component. I have been going over the entire wiring harness to make sure of any possible faulty connections. Is there a site that I could get the exact PCM pinout for my old Ram? I was noticing several different ohm readings while testing grounds and the likes. Not to mention I had a couple of other wires with various ohm readings. I'm sure that several have circuit switches and the likes that effect readings. The manual I have does not give the exact pinout specs, so I'm leary to trust in all my findings without the proper specs to back it up. Just a few parts away from running!!!! LOL

 

One thing that you don't want to do is to measure anything that is tied into the PCM without disconnecting the three connectors themselves from the PCM.

WHY? Sometimes, there's an issue when sending meter voltage through certain circuits thus FRYING components. It's one thing to measure VOLTAGES and OHMs and to buzz out / continuity tests but, some components do not tolerate it and internally pop like a fuse. FYI on that.

So, if and when you're taking measurements or, running continuity checks, always keep that in the back of your mind along with noting what circuit is being tested.

I bought a lot schematics through dealers for a few years in a row until they stopped selling me the schematics for some unknown reason. Short of calling an engineer at Dodge directly, I have no idea of a legal site to download the pinout diagram in FULL but, I will tell you what you can do as an alternative just like I had to do before I got any drawings, is to simply remove the connectors and, start tracing each one out at a time. IN fact, (memory recall) I do believe that one of those cheap manuals (Haynes / Chilton) has an almost complete pinout diagram- yes, in fact, I am now certain that the Haynes manual does indeed contain a partially diagrammed pinout diagram.

NOTE: the color codes may not be accurate. I went through a dash fire in the cab of my truck on the way cross country (failed light switch), in which, I had used it (resides in the cab at all times in case of emergencies) for reference and noted the color coding was NOT accurate thus, their color coding did not match what I was seeing.

Now, the questions are as follows:

Is there power seen on any level?

What was the outcome / test results of anything that you've performed?

Did you see voltage / spark for any period of time or, power to the primary at the coil?

Did you verify voltage TO the PCM?

Did you verify the grounds or, at the very least, remove them all one by one and clean, de-oxidize them either by mechanical or chemical means?

How about mating an un-mating all connectors on the firewall and at the PCM and retesting?

Those are the things that I would run through. I also run through each one - one at a time until I get some results. I then know which one to isolate as the root cause so I can focus on fixing it 100%.

CM