CAN BUS Troubles - Jeep JK fitted with Hemi engine

French Chris · Post by **French Chris** » Sun Jan 31, 2021 5:58 pm

Hi everyone,

I am desperate for help as the way things are at the moment my Jeep is almost unusable.

Please let me explain a little about this built. This a 2008 Jeep Wrangler JK which used to be fitted with a 3.8 L V6 engine and an Auto 4 x speed Transmission when it was stock.

3 years ago I imported from Florida a 2014 Dodge RAM 5.7 L V8 engine with low mileage and I bought a 2nd hand 5 x speed auto transmission from England. I want to say that I am not the only one who has carried out this conversion. In USA and in Europe there are dozens of Left Hand Drive Jeep JK fitted with that engine and after market "Hemi kit" which includes of course an ECU and wire Harness. In UK I am pretty sure that I am still to this day the only RHD JK owner with that engine on board.

The conversion was done by a Pro from West Yorkshire and all used to work fine but gradually I started to get intermittent CAN Bus faults. With time things went worse and since last year I got stuck in more than one occasion with a Live CAN Fault and I was unable to restart the engine.

I spoke to a couple of Auto Electricians in my area but as soon as I told them that was not the original engine and ECU they were not interested.

So I started studying how CAN Bus circuits are designed and bought a Reel of Belden Alternative 8760 cable.
I ran my cable from the ECU/PCM in the Engine bay to the WCM under the steering wheel. These two modules are the ones fitted with a 120 Ohms resistor. Then from the main cable I ran a splice to the TIPM (Main Fuse box), another one the ABS module, and inside the Cab another splice for the ORC Module and one for the SAS.

Having done that all my CAN Bus faults had cleared. ( I will give the list of DTCs below). I tried the Jeep only for short distances as my MOT had ran out so all looked OK to me.

I drove the Jeep to the garage a couple of weeks ago. The garage is only a 10mn drive and all was still ok. I left them for about 1 hour and when I came back to pick it up I was told that it failed MOT due to an ABS light in the dash. There was no light in the dash when I left the Jeep with them but I told them that I would take it home to sort it out and bring it back. Unfortunately it was not possible to restart the engine. The battery was good but I knew immediately that my CAN Bus faults were back. They lent me a Scan tool and I managed to clear the faults and to start the engine.

The following day I cleared the fault, brought it to the garage, they checked that the ABS light was gone and they passed it so at least it is now Legal to drive.I drove it the following day for almost 1 hour with no issue. Then I stopped to put Petrol in it and after a 10 mn drive from the petrol station all lights in the dash flashed at me: the ABS, the Airbag, the handbrake light.

I have since ran my Picoscope 2204A but I am very new to this and I struggle to make sense of the Graphs.

So I enclose a couple of readings and the Electrical drawings that I followed to rewire my CAN Bus. The list of DTCs is: ABS Module: U002 CAN bus off performance. U0101: Lost Coms with TCM. U0126: Lost coms with SAS. U0141: Lost coms with TIPM. ORC Module: U002 and U041. SAS Module: U001: CAN C Bus. and U0141. WCM U0141. CGW: U0121: Lost coms with ABS and U001 (Active every other DTC were Stored).

Your help will be greatly appreciated.

French Chris · Post by **French Chris** » Mon Feb 01, 2021 7:47 am

Hi again,

I just realised my attachments did not upload so I try again.

French Chris · Post by **French Chris** » Mon Feb 01, 2021 8:11 am

I tried to upload this video I recorded on Wednesday 26th Jan but even Zip compressed the file is too large.

I had my Scan tool connected to my breakout box and also connected to my Pico 2204A.

That was just to show you that what really puzzles me is that with the ignition on I had almost no signal and both CAN H and CAN L stay at around 2.5V but as I was reading and clearing the faults my Scan Tool instructed me to turn the ignition off and then there was a signal going from about 2.5V to about 3.7V on CAN H and to about 1.6 V for CAN L. The signal looks really weird but I have nothing to compare it to.

Post by **Steve Smith** » Thu Feb 04, 2021 5:55 pm

Hi Chris and thank you for the post, sorry for the late reply

We have a lot to get through here but first let’s start with your scope and settings.

Scope: The 2204 is a pocket rocket for sure but please have a read through the forum post below as you are missing so many features that can help your diagnosis here.
topic19501.html?&p=87821&hilit=2204#p87821

Having access to the Guided Tests within the automotive software (with an automotive scope) will allow to capture sufficient data to decode multiple CAN messages with sufficient resolution and sample rate

Settings: At present your scope has captured CAN messages but only individual messages at 50 µs/div. Your captures also include triggers which offers very little in the way capturing events. You can liken your current scope settings to looking at CAN traffic through a microscope, here you can see each message passing through.

We need to use settings that are more like looking at batches of CAN traffic (over as slower time frame) and then use the zoom features of the software to view the data in greater detail (Like using binoculars from a distance)

I can see you have used x20 attenuation for each channel, were you using high impedance probes?
Ideally the following scope probes will help https://www.picoauto.com/products/test- ... 00-mhz-bnc using the x10 setting.

Based on your description of the fault “no signal and both CAN H and CAN L stay at around 2.5V” we need to monitor the CAN bus over a slow time frame (minimum 200 ms/div)

The following forum posts will help you capture intermittent CAN bus faults using Masks and Triggers post94181.html#p94181 viewtopic.php?p=89171#p89171

These setting will help if your physical layer is failing resulting in interruption of CAN messaging

If your CAN messaging errors are not related to the physical layer, then serial decoding is required and this is where the Guided Tests would help configure your automotive scope to assist you further

The following video will help https://www.youtube.com/watch?v=Bc2R462 ... Automotive

This forum post looks at how you determine “Who’s on line and Who said what?” topic21680.html

Please note your scope may present a number of limitations when it comes to decoding and therefore please consider such during your diagnosis

The following forum post looks at the limitations of using PicoScopes as a CAN Logger viewtopic.php?p=98467#p98467

Finally, the following forum post/video will help you use your scope in conjunction with a scan tool to capture momentary events using screen recording software
viewtopic.php?p=100929#p100929

There is a lot to plough through here Chris and I would urge you to consider once again your choice of scope for this task

I hope this helps, take care…..Steve

French Chris · Post by **French Chris** » Fri Feb 05, 2021 4:31 pm

Hi Steve,

First I want to thank you for taking the time to write such an helpful reply.

I must be honnest with you I bought my 2204 after watching some Videos on YouTube from a guy who (without blaming him) intends to lead people to think that all they need is a £100 Picoscope to sort out their CAN Bus problems. At the time of my purchase I was not even sure I would be using it at all and I decided to rewire my CAN Network thinking that I would cure the faults. Which strange enough did it while the Jeep was at standstill in the garage or for very short drives.

It's only now that I am starting to realise that I should have invested in a proper scope. I was also wondering why I could not access to the Library and the Guided Tests.

Nevertheless I will read all the information you sent me and try to digest it and I will try to improve.

To answer your question I am using 20:1 attenuators with Hantek HT30A Test leads. I am not sure what is the physical layer but at looking at the Graph you sent me it is clear that I have an intermittent Short between Can H and Can L. Problem will be to find where as I am pretty sure that does not come from my new wiring. The only module that I have a doubt is the ORC. The thing is I am wondering if I was disconnecting it from the Can bus in order to run a new Test, if I would make things worse or even if that would trigger an Air bag deployment.

Thanks again for your help Steve. I will keep you updated.

French Chris · Post by **French Chris** » Wed Feb 17, 2021 9:50 am

Hi Steve,

I am back for a little bit more advice if you could please.
I apologise for the long time with no update with the cold weather I didn't go to my Jeep for a while as the garage I rent is like a freezer.

I tried to follow your advice : "Based on your description of the fault “no signal and both CAN H and CAN L stay at around 2.5V” we need to monitor the CAN bus over a slow time frame (minimum 200 ms/div)"

Here is the result with ignition on with a slow time frame of 200ms/div and a sample rate of 1MS, then down to 100ms/div.

I even tried my luck with the Serial decoding option but I got a warning sign telling me that my Sample rate might be too low and I couldn't get any data.

Sorry to be a pain but I am really lost here.

liviu2004 · Post by **liviu2004** » Wed Feb 17, 2021 11:14 am

On a short look in all waveforms, seems to be no comm at all. Something is wrong with your capture.

-20/+20V scale does not do any good. -5 to +5V would be ideal. We need to learn how you actually connect the scope, if any atenuators are used. No triggers to be used.

No point trying to decode something which does not exist.

Looks like no module wakes up, unless CAN H to CAN L is short circuited. Which can be simply confirmed with an resistance measurement between H and L, 60 ohms.

French Chris · Post by **French Chris** » Wed Feb 17, 2021 12:57 pm

Hi Liviu 2004,

Thanks for having a look at my problem.

Usually I connect my leads to my 20:1 attenuators and I set my probes to Channel A and B to x20 but yesterday I didn't use any attenuator so my probes were set up at x1. My leads are connected to my breakout box on Pin 6 for Can H and 14 for Can L. Both black leads are connected to Chassis ground. I run the Picoscope 6 Software first then I connect my Picoscope via the USB lead to my Laptop.

I have done dozens of resistance Tests from the breakout box between Can H and Can L and I always get 60 Ohms. The 120 Ohms Resistors are in the PCM in the engine bay and in the WCM under the steering wheel. I took resistance measures between Can H and Can L at the PCM connector (disconnected from PCM) and got 120 Ohms. I did the same at the WCM connector (disconnected from WCM module) and got 120 Ohms.
I took the resistance measure between Can H and Can L at the ABS connector (disconnected from ABS but the PCM and the WCM module were connected ) and got 60 ohms. All these measures were taken off course with the Battery Negative lead disconnected.

What is weird is that at times I get a signal. Not particularly a nice signal but I do get one when connected to Signal Ground instead of Chassis Ground like in the Graph taken a couple of weeks ago on 02nd Feb a12:02 hour. Then I took the measure instead with Chassis Ground at time 12:13 and back to Signal Ground a second time at 12:18 and both Graphs were showing Can H and Can L stuck to about 2.5 Volts.

I just noticed that both Graphs taken at 12:13 and 12:18 had a trigger on but not the Graph taken at 12:02. Would the trigger has anything to do with it?

liviu2004 · Post by **liviu2004** » Thu Feb 18, 2021 7:23 am

Sorry, on mobile and can’t see waveforms.
Rule #1

trigger to OFF and stays off.
Rule #2: ground reference is always battery negative.

French Chris · Post by **French Chris** » Thu Feb 18, 2021 8:48 am

Thanks for that Liviu2004,

I will try again this morning without trigger and I will only connect my probes to chassis ground instead of signal ground from now on.

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