CAN Bus wave pattern for 2007 Jeep GC WK?

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Jake Murphy
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CAN Bus wave pattern for 2007 Jeep GC WK?

Post by Jake Murphy » Tue Aug 27, 2019 2:03 am

Using a Pico 4425 and Pico BOB I've been trying to get a CAN Bus trace on a 2007 Jeep Grand Cherokee Limited 5.7L . Pins 6 and 14 are supposed to be CAN C (high) and CAN B (low). There is very little voltage change on a +/-5v scale. It looks like one line above and one line below 2v with noise. When I stop and try to zoom in, the two traces are not close to being a typical CAN Bus pattern. I used the same set up, same settings on a Chevy Suburban with no problems.

Iver
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Re: CAN Bus wave pattern for 2007 Jeep GC WK?

Post by Iver » Tue Aug 27, 2019 10:50 am

Pins 6 and 14 are supposed to be CAN C (high) and CAN B (low)
Well Yes and No !! Common misconception nowadays, it does depend on the Topology of the Network and whether or not the car has a Communication Gateway. A wiring Diagram will tell you that.

The days of seeing anything other than "Diagnostic" CAN at 6 & 14 are slowly going with the introduction of Gateways.

Measuring at 6 & 14 is no longer the right way to solve some CAN bus issues.

Are you experimenting or does this car have a fault ?

Try that same measurement again with your Scan tool plugged in, communicating with a controller reading Live Data

vasek
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Re: CAN Bus wave pattern for 2007 Jeep GC WK?

Post by vasek » Tue Aug 27, 2019 11:40 am

Jake Murphy wrote:
Tue Aug 27, 2019 2:03 am
the two traces are not close to being a typical CAN Bus pattern. I used the same set up, same settings on a Chevy Suburban with no problems.
Hi.
There is a fundamental difference in the connection on the diagnostic connector DLC 16.

DLC 16 Chevrolet:
6 pin - high speed GM Lan BUS+
14 pin - high speed GM Lan BUS -
Powertrain CAN BUS , with constant data flow.
When the ignition is on,there is a constant exchange of data between the units.

DLC 16 Jeep (early production before 2008):
6 pin - CAN C+
14 pin - CAN C-
This CAN BUS is a diagnostic BUS from the Scanner to the ECU FCM (front control module with gate-way function)
The signal on this BUS will be only if there is a Scanner-FCM dialog
1 pin - CAN BUS+
13 pin - CAN BUS -
Powertrain CAN BUS , with constant data flow.
When the ignition is on ,there is a constant exchange of data between the units.

DLC 16 Jeep (after 2008):
6 pin - CAN C+
14 pin - CAN C-
This CAN BUS is a diagnostic BUS from the scanner to the ECU FCM (front control module with gate-way function)
The signal on this BUS will be only if there is a Scanner-FCM dialog
1 pin - not used
13 pin - not used
There is no Powertrain CAN BUS on the diagnostic connector.
The Powertrain CAN BUS may be measured directly on the connector of any Powertrain ECU.

Iver
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Re: CAN Bus wave pattern for 2007 Jeep GC WK?

Post by Iver » Tue Aug 27, 2019 12:05 pm

The Powertrain CAN BUS may be measured directly on the connector of any Powertrain ECU
Indeed yes. Or better still if the "Gateway" is accessible then what a great place to start. One place to look at all the Communication Networks in the car. Curve ball being that there could be more than one Gateway.

Jake Murphy
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Re: CAN Bus wave pattern for 2007 Jeep GC WK?

Post by Jake Murphy » Tue Aug 27, 2019 2:14 pm

Iver wrote:
Tue Aug 27, 2019 10:50 am
Pins 6 and 14 are supposed to be CAN C (high) and CAN B (low)
Well Yes and No !! Common misconception nowadays, it does depend on the Topology of the Network and whether or not the car has a Communication Gateway. A wiring Diagram will tell you that.

The days of seeing anything other than "Diagnostic" CAN at 6 & 14 are slowly going with the introduction of Gateways.

Measuring at 6 & 14 is no longer the right way to solve some CAN bus issues.

Are you experimenting or does this car have a fault ?

Try that same measurement again with your Scan tool plugged in, communicating with a controller reading Live Data
As per the factory shop manual, the above configuration is correct. No faults, just learning.

Jake Murphy
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Re: CAN Bus wave pattern for 2007 Jeep GC WK?

Post by Jake Murphy » Tue Aug 27, 2019 2:21 pm

vasek wrote:
Tue Aug 27, 2019 11:40 am
Jake Murphy wrote:
Tue Aug 27, 2019 2:03 am
the two traces are not close to being a typical CAN Bus pattern. I used the same set up, same settings on a Chevy Suburban with no problems.
Hi.
There is a fundamental difference in the connection on the diagnostic connector DLC 16.

DLC 16 Chevrolet:
6 pin - high speed GM Lan BUS+
14 pin - high speed GM Lan BUS -
Powertrain CAN BUS , with constant data flow.
When the ignition is on,there is a constant exchange of data between the units.

DLC 16 Jeep (early production before 2008):
6 pin - CAN C+
14 pin - CAN C-
This CAN BUS is a diagnostic BUS from the Scanner to the ECU FCM (front control module with gate-way function)
The signal on this BUS will be only if there is a Scanner-FCM dialog
1 pin - CAN BUS+
13 pin - CAN BUS -
Powertrain CAN BUS , with constant data flow.
When the ignition is on ,there is a constant exchange of data between the units.

DLC 16 Jeep (after 2008):
6 pin - CAN C+
14 pin - CAN C-
This CAN BUS is a diagnostic BUS from the scanner to the ECU FCM (front control module with gate-way function)
The signal on this BUS will be only if there is a Scanner-FCM dialog
1 pin - not used
13 pin - not used
There is no Powertrain CAN BUS on the diagnostic connector.
The Powertrain CAN BUS may be measured directly on the connector of any Powertrain ECU.
Thank you.
1. What is the source of your information? Can you share a link?
2. Per the factory manual the diagnostic bus that communicates with a FCM/ scanner is called Diagnostic CAN C or CAN D.
I'll try out and give you a shout back.
I will attach my scanner to the BOB and see what happens when they communicate. Thanks.

Jake Murphy
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Re: CAN Bus wave pattern for 2007 Jeep GC WK?

Post by Jake Murphy » Wed Aug 28, 2019 12:10 am

The 7000 page shop manual pin out for the DLC on the 2007 Jeep GC WK shows no circuits on pins 1 and 13. It only shows CAN C Diagnostic on 6(+) and 14(-). I'll check myself later this week if there is anything on them.

vasek
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Re: CAN Bus wave pattern for 2007 Jeep GC WK?

Post by vasek » Wed Aug 28, 2019 5:42 am

Jake Murphy wrote:
Tue Aug 27, 2019 2:21 pm
What is the source of your information? Can you share a link?
All this is in the schematic diagrams (MOD).
Perhaps they have inaccuracies.
But this does not change the meaning, there is no activity on the CAN DIAGNOSTIC line in the absence of the scanner-gateway dialog.
On the CHEVI SUB connector, you connect directly to the CAN POWERTRAIN.
Attachments
JEEP GC 2008.png
JEEP GC 2007.png
JEEP GC 2006.png
CHEVI SUB 2007.png

Jake Murphy
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Re: CAN Bus wave pattern for 2007 Jeep GC WK?

Post by Jake Murphy » Wed Aug 28, 2019 12:29 pm

Thank you for the wiring diagrams. Tomorrow I am going to do a number of things:
1. Monitor 6 and 14 with a bidirectional scan tool attached.
2. Check 1 and 13 for voltage and resistance.
3. Check 1 and 13 for a trace.
I'll let you know what happens.

Jake Murphy
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Joined: Thu Aug 30, 2018 12:55 am

Re: CAN Bus wave pattern for 2007 Jeep GC WK?

Post by Jake Murphy » Thu Aug 29, 2019 11:53 pm

OK, so here's the f/u:
1. I connected my Autel MS906BT to the BOB and I was able to get a normal CAN Bus pattern at 6 and 14.
2. Pins 1 and 13 have no voltage with KOEOff or KOERunning. There is no continuity between 1 and 13. The wiring diagram must have an error.

Thank you very much for your assistance.
Best regards,
JM

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