Cooling Fans On High Cause CAN network Interference

Ryan Owner/Technician Alabama Posted   Latest   Edited  
Resolved
Electrical
Network Communications
2014 Scion tC 2.5L (2AR-FE) 6-spd (U760E) — JTKJF5C71E3073014
P0500 — Vehicle Speed Sensor "A" Circuit
P0793 — Intermediate Shaft Speed Sensor "A" Circuit No Signal
Warning Lights And Codes Set When Fans Come On High

This vehicle sets P0500 in all modules that can set it and I get heavy CAN interference whenever the fans are on high. Most noticeably when you turn the a/c on and the vehicle is moving and the fans kick on. I can disconnect the fans and the interference goes away. What I mean by interference is the CAN signals go from 0-10 volts whenever the fans are on but still produce the same waveform. It does it with either fan on or both on. I can run each fan off a separate fused power and ground supply straight from the battery and the interference does not occur. The Fan powers come straight from the engine fuse box and come out the front and go to the fans so not very much there and everything appears factory including the harness, fans and fuse box. I wouldn't think the fans would have failed and caused this because it does it with either fan and the only connection to the CAN network is the ECM supplying ground to the relays but it still does it when supplying power to the relay terminals and the relays out. Any ideas? Thanks

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Interesting
Dan Owner/Technician
Texas
Dan
 

… Following … Dan H. … Hobbs … South Texas …

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Tony Owner/Technician
Missouri
Tony
 

Did you capture a waveform of CanH and CanL with and without this “interference”? What is the resistance across H and L? Toyota doesn't show diodes in the A/C clutch and/or fan circuits any more, I wonder if the relays have diodes integrated and one failed? There should be a diagram printed on each relay.

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Agree
Benjamin Owner/Technician
Georgia
Benjamin
 

That’s a good point, I’ve noticed sometimes bad relays I’ve replaced I have noticed on some of them, if you shake it you can hear the clipping diode broken and just rolling around inside the relay

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Jose Technician
California
Jose
   

Right off the top of my head i would suspect poor Ground. Can you perform a voltage drop on the ground side, while problem is occuring?

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Glenn Owner/Technician
Texas
Glenn
 

Hello Ryan, I am inclined think you have a ground issue. Any history of body damage or body repair? It is a good idea to start at the battery and loosen, clean and retighten, then go around the chassis and do the same with all other grounds.

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Robby Technician
Alabama
Robby
 

Hi Ryan, It's not uncommon for electrical components to induce noise into the CAN signals. Fault tolerance is one of the main benefits of CAN. If you scope the signals with one lead across CAN-H and CAN-L, do you still see the interference? Another idea is to scope that fan motor current along with CAN and see if the noise syncs up. My initial thoughts are if there was that much abnormal…

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Ryan Owner/Technician
Alabama
Ryan
 

Here is the scope capture but I actually figure it out as well! On high the fan grounds were at 5 volts. I traced it to the left front fender where they painted every fender contact point so cleaning the fender contacts and grounds repaired the ground and CAN signals.

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Glenn Owner/Technician
Texas
Glenn
 

Hello Ryan, From past experiences with shared or “piggyback” grounds, I recommend you separate the CAN harness ground away from the fan ground, so it has a clean uninterrupted ground. The reason being is as the fans wear, they will start to resonate back feed into their ground, this will scramble the CAN if it is joined.

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Ryan Owner/Technician
Alabama
Ryan
 

I'll get some scope captures and check the grounds and relays once I get some time here in a little bit. I appreciate all the help guys!

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Ryan Owner/Technician
Alabama
Ryan Resolution
   

The fan grounds were at 5 volts on high. They ground at the left front fender and someone painted all the contact points for the fender so I cleaned the contact areas and now we have good grounds to the fans and no more CAN interference.

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Thanks
Dan Owner/Technician
Texas
Dan
 

… Post a resolved then . … Dan H. … Hobbs … South Texas …

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Ryan Owner/Technician
Alabama
Ryan
 

It won't let me for some reason.

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Scott Manager
California
Scott
 

Hi Ryan, Reply to your original post with your new info and then you'll be able to mark it as resolved.

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Dmitriy Analyst
Ontario
Dmitriy
 

That works for Questions, but the thread was started as a Discussion…

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Ryan Owner/Technician
Alabama
Ryan
 

Changed it to a question and now it's resolved. Thanks!

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Scott Manager
California
Scott
 

Thank you!

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Scott Manager
California
Scott
 

Oops, my bad, I didn't realize his question wasn't originally tagged as a question.

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