[Tbarker3440]

2008 Santa Fe Limited 3.3l AWD with crank no start. Have fuel, spark, compression - suspect timing is off. Bought a Launch X431 bi-directional scanner. It shows codes that my older cheap reader does not. 3 codes set by the ABS/ESC system - all to do with bad communications:
C1616 Communications Bus Off
C1513 Brake Switch Circuit (this might be over a year old as I did change this switch)
C1702 Variant Coding Error (the ESC module)
U0001 CAN Communication Malfunction

Given that a Dodge product I once had had a no-start because of the TPMS module failing, I thought I would tackle the U0001 first to see if it cleared the rest up. I bought an ALLDATA subscription and got the service procedure.

First check is on the resistors made at the data port. 121 ohms on single lines, 61 ohms between the lines. In spec.

Check 2 : Is there a short to ground? Short answer is YES but after 10 hours of trying to chase it down Im stumped. I tried to isolate each leg of the circuits to test the wiring and the device. There are 4 devices : PCM, Steering Angle Sensor, 4x4 ECU, HECU. And the wires go through the under dash fuse box. When isolating stretches of the circuits, I found no instance where there was a path to ground without a device plugged in. When plugging in each device one at a time, ALL of them showed a resistance reading to ground. I was expecting one to. (all of these are measured on the High line). The car ran fine and smooth, was shut off normally and then wouldnt start.

Steering angle sensor - 25 M ohm.
PCM: 13.4 K ohm
4X4 ECU: 25 K ohm
ABS/ESC 21 K ohm

If I plug them all in at the same time in parallel like normal : 14.7 K ohm to ground. I disconnected the I/P fuse box with no difference in any readings. I took the readings from all points along the harness - no difference.

I cant find any water damage, chafing, pulled wires - no visible sign of damage. My ordered scope has not arrived yet so cant test wave forms for a few days.

My Question: These ohm measures are high resistance but the book says they should be infinite. They all occur through a module - Is this normal? What do I do next?

 

[Gerard 2]

I'll play devils advocate because I'm not fully understanding how you've performed the test for short. I'm looking at a fault finding process which reads similar to what you describe but in a Euro market vehicle.

So you say you found short to ground. I'm reading all modules isolated, then test resistance to ground from pins 3 and 11 on the OBD2 port. You say short.

But then you connect modules and you have high resistance.

If it was short isolated it would also be short with modules connected?

Or, am I not getting it and you're implying short only on CAN LOW but CAN HIGH is ok?

I've never done anything on a vehicle down to this level on a CAN BUS, so I'm not claiming to know for sure, just trying to understand the results.

 

[Tbarker3440]

All of the ohm readings I provide are for the High line just to make the post simpler. I disconnected all devices and a joint splice which places PCM, Hecu, and 4x4 ECU in parallel. I also disconnected the I/P fuse box in this state, I probed a known good chassis ground with one lead and the appropriate harness connector pin for the High line with the other lead. The only way to get a reading doing this is if the wire probed has a path to ground (like a chafed exposed wire touching something metal) I did this at several points along the harness path starting at #3 pin on the data link port. None of the circuit legs I isolated this way showed a path to ground

All of them have a reading when the device is plugged in. The steering sensor has a massive resistance and the other three have high resistance. Or at least I think they are high. I was thinking they should be infinite too.

Hoping a trained tech here might help 'calibrate' my thought process

There are further tests but it seems pointless to proceed until I resolve that this step is explained