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Hello-
I did the following test related to a no communication to my scanner. Symptom is nothing turns on when key is in the ignition. I mean nothing- the only thing that lights on the dash is the door ajar light. Scanner cant communicate when hooked up. Heres what I tested and checked so far. Yesm the Battery voltage is fine as well as the fuses and relays:
1. Verified that Battery voltage is getting to the PCM
2. Verified all ground wires on the PCM are good
3. Tested the TPS and MAP sensors 5V Reference and got 0 Volts
4. Tested DLC pin 16 and have Battery volts
5. Tested DLC pin 6 to pin 14 and have 60 Ohms (Terminating resistor in PCM)
6. Tested DLC pins 4 and 5 to verify grounds
7. Tested DLC pin 16 to pins 4 and 5- got Battery voltage
Heres what Im concerned with:
DLC pin 6 (High Side) is showing .016 Volts
DLC pin 14 (Low Side) is showing .016 Volts
Any suggestions or help would be much appreciated. Thanks-
"The object of war is not to die for your country but to make the other bastard die for his"
If you have verified ALL of the POWERS and GROUNDS of the PCM are good, and you have no 5 volt reference, that is a good indication of a dead PCM. Verify that the 5 volt REF is not shorted to ground, and stick a fork in it. Without knowing the YMM, there is not much more help that can be offered. Can you communicate with any other modules?
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer." I have learned more by being wrong, than I have by being right.
There are cars (VW,Chryslerfor example) with a dedicated "net just between the dlc and the gateway. As Chad pointed out YMM is a must for meaningful assistence, with the information given you can NOT condemn anything.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
The following user(s) said Thank You: Tyler, MrMike
The DVOM is just fine for can bus testing. It will take you a long way while knowing what to look for.
That said, as a quick check if you're concerned about the pcm, you may want to disconnect her and see if something changes, other modules communicate now etc
If nothing changes you should grab a wiring diagram and confirm the integrity of the can bus wiring. These tests have to be done on the CAN C side of the bus, means upfront of the gateway. You always can check there for the corresponding voltages as well. It might be necessary to disconnect more modules at one time.
As Chad already mentioned: if no other problems are found you may have to test/disconnect the 5 V reference circuits and their components.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
When you say "CAN C side of Bus", where is that located? Also; to be honest; Im not sure where the other modules are on my truck, like location wise. I did take the PCM out the other week and brought it in the garage and looked it over real good for any bent pins, water damage, burn marks, ect. and it looked fine on the outside. I will re-check the 5V Ref circuit and make sure its not shorted anywhere. Another question is- if I do need a PCM, do they make them to where they are pre-programmed to the VIN? Im asking this because if I have to have the truck towed to a dealership or shop, its going to cost me more for the tow than what I probably will pay for the PCM. Keep in mind, Im no Master Tech and is why Im asking these questions. Thanks Much-
"The object of war is not to die for your country but to make the other bastard die for his"
CAN C side means to tap into the actual bus wiring where all the modules physically are connected to. This CAN C bus will finally connect to the gateway, so you can tap into the INPUT from the can bus to the gateway. The OUTPUT of the gateway is denominated CAN D, like diagnostics, and only is the section from the gateway to the DLC. This part does not allow to see everything that actually could be bad in the CAN C portion.
Yes, you can order a plug and play controller with the VIN already programmed to it, hth.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
Ok- knowing that you can buy a PCM and plug it in is good news for me since I live a ways out. As far as the CAN- what do these normally look like and are they hard to locate. I think I might have an idea of what you are talking about but I'm not real sure.
"The object of war is not to die for your country but to make the other bastard die for his"
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer." I have learned more by being wrong, than I have by being right.
So, if Im looking at this correctly, all of the modules are actually ECU's that are inter-connected by the CAN lines? Do each of the modules have its own terminating resistor or are those only located inside the PCM? Would it be a good idea to test the ABS module as well for power and grounds? I did do a check yesterday for voltage directly at the PCM's 5 Volt ref wires on PCM connectors C1 and C2 and both had no power, so this no power was verified not only at the sensors, but also at the PCM. In your opinion, is there any further testing I should do to confirm the PCM is at fault? Thanks for the diagram. Im going to print it out and look at it more closely.
"The object of war is not to die for your country but to make the other bastard die for his"
In a high speed can bus there are only two nodes/modules that feature a 120 ohm resistor each one of these two. These two resistors are wired in parallel resulting in 60 ohms network resistance.
One principal characteristic of a can bus is that all nodes (Chrysler term for ECU, controller, module etc) are connected to the common net, bus actually is the name of this physical structure, the wiring itself.
Chad's diagram shows the bus between gateway, tipm in this case, labelled as CAN C. I was wrong to call it CAN D. And what I called CAN C in the diagram is referred to as CAN only (high speed CAN), . Regard this when trying to test at the referred locations mentioned in my earlier reply.
You still may have a shorted to ground 5V reference wire or sensor.Now you can disconnect each and every sensor one after another until the 5V come back if there was a short. If you had a shorted 5V reference wire the 5V won't come back even after disconnecting all sensors. You may cut these reference wires close to the connector on the pcm side an test again for voltage on the cut wire, pcm side. You should cut all 5V reference wires coming out of the pcm as they internally may be shared
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
Hello,
So regarding the 5V wires- when I tested voltage at the PCM and got .000V, would it still be necessary to disconnect the sensors since I basically tested at the source? Should I test the ABS module power and grounds as well, or would this have anything to do with what Im trying to confirm? Thanks-
"The object of war is not to die for your country but to make the other bastard die for his"
With the reference wires cut and no voltage coming out of the pcm you don't have to disconnect the sensors anymore. This only goes for powers and grounds already verified!
The abs module wouldn't be a concern at this point, for me.
I wouldn't necessarily expect the instrument cluster to fail completely with the suspected bad pcm though. You may want to backprobe pin 34 and pin 35 at connecter 1 at the pcm and take a resistance measurement, it should read 60 ohms. Then disconnect the pcm and put a 60 ohm resistor between the same terminals/pins 34 and 35 and recheck if you then the cluster comes to live with KOEO and communication is restored with the rest of the modules.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
