Intermittent IPC Class 2 serial data communication.

[BigSilver]

2003 Chevy Suburban, 2500, 6L:
Intermittent IPC Class 2 serial data communication. DTC U1000.

I’ve checked the +ve and -ve pin connections on the IPC wire loom
(pins B11, B9 are +ve voltage, and B12 and A12 are ground) and
all are functional in Accessory and Run modes.

Pin A6, the Class2 serial data input feed is what needs to be verified,
or at least the wire feed itself, that supplies the serial data.

How would one go about testing for the serial data on the input lead A6,
without the IPC?

Where could one locate the opposite end of the input wire feed of the
Class2 serial data input feed, to determine if its sound? At the BCM module, or elsewhere?

[farmtruc]

Are you wanting to verify if data is coming out this wire, or if the wire just has continuity?
Acquire some schematics and pin it out for continuity testing.
For data, I'm sure it takes a bit more.

[decibles]

I don't know what or why you are wanting to follow this wire, but if it is for the purpose of troubleshooting the U1000 code you might look real closely at the ignition switch I have seen them lose one circuit in the crank position and cause this code. Another thing to check is the harness grounds and if this vehicle has an aftermarket theft deterent or remote start they could be causing it also. One important thing to remember is that if you use the scan tool and check for codes in the other modules (bcm, ipc, chassis/abs) you can narrow down the cause every module shares the sam data link so if you find a loss of communications with the ipc in any other modules the problem is likely a int. power drop the ipc or a bad ipc. Another important thing to consider if the PCM lost coms with the PCM it should have set an IPC code for loss of coms with pcm if it didn't then definately gotta be an issue with the ipc itself good luck and a little more info i am sure I can walk you through troubleshooting this.

shane

[BigSilver]

Thanks for your points of view fellas.

The intention is too check the internal resistance of the wire feed that caries the Class2 serial data. I feel it may be the culprit. When its freezing cold, and the IPC doesn't wake until one just touches the plug or sometimes just its wire bundle. Other times it may be necessary to flex the plug.

With the last scenario I figured the pcb might have a cracked circuit lead, so I added redundant wire feeds onto the circuit board, starting from the pin harness, see photos.
IPC trace addon1.jpg
Class2SerialShroudedRed.jpgThe wire lead with red insulation is the serial input feed.
IPC traceadd_ons.jpg

With the circuit mod there appears to be more repeatable IPC wake-ups in freezing weather. In those instances when it fails, just a touch to the wire loom or plug, is all it needs to nudge it into operation. This is why I'd like to check the wire's continuity, that feeds the serial data.

If the wire is not at fault, then it may be a a faulty input capacitor on the circuit board. Another words, the touch of the hand to the IPC may somewhat affect the board's relative capacitance (a hypothesis).

Other present DTC's before the circuit mod:
U1096 - lost communication w/ driver info and display control system (IPC);
U1152 - lost communication w HVAC control system;
B0283 - electric rear defrost;
B1440 - Power mode master input circuit mismatch;
B2600 - passenger compartment dimming 1 circuit.

[decibles]

If you really suspect the wires continuity then run another one I have done this before and and simply soldered them in near the connectors on either end. I understand what you thinking about the capacitance however if you consider this is a dc circuit capacitance is impossible unless you had a shielded wire(coax etc) which was completely open on one end. Another thing to remember is that lower temperatures mean less resistance the opposite of what I think you are proposing. I will almost guarantee you have power issue with one of the ignition circuits due to the codes you have listed. Unless they are happening at unrelated times. Do you have a scanner, I don't know if aftermarket will give you freeze frame and failure records so you can see if they occur at the same times. I know I am kinda spoiled since I own a tech II which in your situation would make this diag. simple. You could monitor class II coms status and message when you experience the problem. I am 90 percent sure the wire isn't the issue since it is a common circuit for all modules and if one had high resistance you all most always lose 100 percent coms incl the scan tool coms. I hope this info helps. by the way you could completely disconect the class II feed from the ipc and the ipc will still power up. if you don't get any power up from the ipc you need to look for a boken wire inside the insul or bad pin fit going into the ipc.. I have been down the road you are headed, and let me tell you in my experience the data link is the least likely cause. I know that not what you wanna hear but the fact that you are setting a serial code in only some modules is a good sign it is a power or ground issue.

[farmtruc]

sounds like the typical open wire in the GM harness

[BigSilver]

I appreciate your approach to the issue. Words of wisdom are bitter at first, but sweet in hindsight.

Fortunately I do have the techII. Whenever the IPC is down and the ignition is set to “on”, with engine off, the techII has indicated a communication failure. Communication can only be regained with the engine on.

I’ve checked the input power and ground lines of the IPC wire loom, and they’re all functional. Even when the IPC is down and not displaying the vehicle’s stats, the IPC has power – even a faint hum is audible from the stepper motors.

The ignition-key switch-module has been replaced. The old one (original), after inspection, appeared in top shape. The contact points within the module, were clean and shiny, functioned/connected as per schematic protocol – so that didn’t appear to be the problem.
IgnitionModule4.jpg

For what its worth, with ignition on and engine off, the TechII showed that the radio communication status was oscillating between yes and no. I would have to revisit this area on the scanner, as my memory is spotty here.

The radio though, has not exhibited any malfunctions as yet.

[decibles]

well this one is a first for me, I have never experienced an ipc that wouldn't communicate with the key on engine off, but would when the engine is running. There are a few things that come to mind though. OK lets look at what changes between those two states key is in the same position either way the only difference is that you have gone to the start position momentarily. That being said the IPC is ultimately responsible for storing security info so upon crank signal you have actually caused the IPC to verify security signal is correct and then send the fuel enable command to the pcm. Then there is the other difference which is that the guages have changed states or the difference in voltage. Wait that is something I have seen befor I had an abs module which would drop class2 coms when voltage was below 12.8. If this were me I would start the truck verify coms with everything then I would pull the fuel pump relay to kill the engine with out changing igntion position and see iif the coms are solid this could possibly eliminate the security triggering the IPC to wake up and could help confirm if it is over sensitive to voltage drops.. hope you find this helpful

[BigSilver]

What your proposing makes sense and ties into what I fished out of the service manual.
Splice pack 205, located at the left I/P approximately at the same hight as the BCM, handles
the Class2 com. This is where eight Class2 com wires intersect. I need to check the condition of this
splice pack and possibly each successive splice pack that is daisy chained together.

[decibles]

Just wanted to check back with you and see if you were able to find the root cause. I am one of those people who lose sleep at night knowing there are people out there who may be needing further technical support! Well not exactly, I just like to hear the end result for future reference.
shane